REESE  LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 
Class 


i~-'' 


T\ 


THE   LATE   PROFESSOR   JOHANN    BAUSCHINGER 
(See  Appendix  A. 


Frontispiece. 


THE 

MATERIALS  OF  CONSTRUCTION. 

A    TREATISE  FOR  ENGINEERS 

ON  THE 

STRENGTH  OF  ENGINEERING  MATERIALS. 


J.   B.   JOHNSON,   O.E., 

Professor  of  Civil  Engineering  in  Washington  University,  St.  Louis,  Mo.  ;  Member 
of  the  Institution  of  Civil  Engineers ;  Member  of  the  American  Society  of 
Civil  Engineers ;  Member  of  the  American  Society  of  Mechanical 
Engineers  ;  Corresponding  Member  of  the  American  Insti- 
tute of  Architects  ;  Member  of  the  International 
Association  for  the  Standardizing  of 
Methods  of  Testing  Materials; 

etc.,  etc.  , 


FIRST  EDITION. 
FIRST   THOUSAND. 


NEW   YORK: 

JOHN    WILEY    &    SONS. 
LONDON:    CHAPMAN  &  HALL,   LIMITED. 

1897. 


<\0 


Copyright,  1897, 

BY 

J.   B.  JOHNSON. 


ROBERT  DRUMMOND,   ELECTROTYPER  AND   PRINTER,  NEW  YORK. 


PREFACE. 


THE  rational  designing  of  any  kind  of  construction  involves  a  knowledge 

of— 

The  external  forces  to  be  resisted,  transformed,  or  transmitted; 

The  internal  stresses  resulting  therefrom; 

The  mechanical  properties  of  the  materials  to  be  employed  to  accomplish 
the  objects  sought. 

Of  these  three  coordinate  departments  of  knowledge  the  first  two  are 
founded  on  the  sciences  of  mathematics  -and  applied  mechanics.  The  last 
one,  however,  does  not  rest  on  any  deductive  science,  as  this  information 
can  only  be  gained  by  patient,  expensive,  and  competent  research.  For 
this  reason  the  third  essential  named  above  has  not  kept  pace  with  the  other 
two  kinds  of  engineering  science;  but,  on  the  other  hand,  it  furnishes  very 
much  greater  rewards  to  the  skilled  investigator. 

During  the  past  twenty-five  years  the  number  of  such  investigators  has 
increased  from  a  scattering  few  to  hundreds  and  even  thousands,  and  these 
are  now  found  in  all  enlightened  nations.  The  results  of  their  original 
studies  and  experiments  are  pouring  in  upon  us  from  all  countries,  in  many 
languages;  and  no  practising  engineer  can  hope  to  even  scan,  much  less  to 
appropriate  and  assimilate,  more  than  a  very  small  part  of  this  vast  wealth  of 
experimental  knowledge.*  In  the  following  work  the  author  presents  to  his 
readers  a  condensed  and  concise  summary  of  such  portions  of  the  knowledge 
now  available  on  this  subject  as  he  has  found  suitable  for  such  a  work.  He 
is  fully  aware  of  its  incompleteness  and  of  its  more  or  less  fragmentary 
character.  Yet  with  all  its  faults  he  believes  it  contains  sufficient  reliable 
information,  not  commonly  accessible  elsewhere,  to  justify  its  .publication  in 
this  form. 

*  The  author  has  one  list  of  original  contributions  to  the  subject  of  the  Strength  of 
Materials  filling  140  quarto  pages. 

Ill 


iv  PEEFACE. 

When  the  work  is  used  as  a  text-book  in  schools  of  engineering  the 
instructor  would  do  well  to  assign  only  such  portions  of  Part  I  as  are  required 
to  supplement  the  student's  course  in  applied  mechanics;  to  have  his  students 
read  Part  II  if  they  do  not  get  this  information  in  other  ways;  to  dwell 
longer  and  with  more  care  on  Part  III;  and  to  call  attention  only  to  such 
portions  of  Part  IV  as  pertains  to  the  particular  course  the  students  are 
taking.  In  this  way  the  hook  may  be  made  intelligent  and  familiar  to  the 
student,  and  so  become  to  him  a  great  and  lasting  aid  in  designing,  testing, 
and  inspecting,  without  requiring  more  time  than  can  be  devoted  to  the 
subject.  This  course  should  precede  or  accompany  an  experimental  course 
in  the  testing  laboratory,  with  which  all  American  schools  of  engineering 
are  now  equipped. 

An  unusual  use  has  been  made  of  stress-diagrams  and  other  forms  of 
graphical  representation  of  facts  and  laws,  no  pains  or  expense  having  been 
spared  in  this  direction.  So  far  as  possible  tables  have  been  omitted  and  the 
original  tabular  data  have  been  incorporated  in  diagrams.  A  law  of  relation- 
ship cannot  be  perceived  from  data  arranged  in  a  tabular  form.  When 
plotted  to  significant  arguments  the  law  not  only  becomes  evident  at  a 
glance,  but  when  once  impressed  on  the  mind  through  the  sense  of  sight  it 
cannot  well  be  forgotten.  To  obtain  this  lasting  benefit,  however,  ttr 
diagram  must  be  intelligently  read  and  understood.  The  reader  is  urged, 
therefore,  to  give  great  care  to  the  study  of  all  the  diagrams  which  accom- 
pany the  text  on  any  subject,  for,  as  a  rule,  the  facts,  laws,  and  conclusions 
to  be  drawn  from  them  are  not  fully  expressed  in  the  text.  The  diagrams 
must  be  considered  as  a  part  of  the  text,  and  they  should  be  read  with  even 
greater  care  than  is  bestowed  on  the  word- embodied  ideas. 

Throughout  the  book,  with  few  exceptions,  both  in  the  diagrams  and  in 
the  text,  the  English  units  of  weight  and  measure  (pound  and  inch)  have 
been  employed.  The  author  is  of  the  opinion  that  until  the  metric  system 
has  been  definitely  adopted  it  is  best  to  use  the  old  unit  •>,  and  that  a  double 
system  of  units  is  confusing.  The  revising  of  books  to  put  them  in  harmony 
with  the  decimal  system  will  be  but  a  very  small  part  of  the  total  expense 
entailed  by  the  formal  adoption  of  that  system  by  our  Government.  As  a 
very  large  part  of  the  data  given  in  the  diagrams  comes  from  Continental 
sources,  all  of  which  were  expressed  in  the  metric  system,  a  great  amount  of 
labor  was  required  to  bring  this  material  into  the  English  system  of  units. 
Even  the  results  obtained  from  English  sources  were  generally  expressed  in 
long  tons  per  square  inch,  so  that  this  also  required  reduction  to  bring  it  to 
pounds  per  square  inch. 

Some  of  the  author's  usages  may  be  regarded  as  unwarranted  innova- 
tions. Especially  may  this  be  the  case  in  the  matter  of  the  new  elastic  limit, 
which  he  proposes  for  general  adoption,  and  which  is  discussed  in  Arts.  13, 
261,  262,  and  263.  The  author  bespeaks  for  these  articles  a  careful  consid- 
eration and  also  a  study  of  the  many  stress-diagrams  scattered  through  the 
book,  before  his  views  are  condemned.  The  fact  is,  something  must  be  done 


PREFACE.  V 

in  this  matter,  as  now  no  one  knows  what  is  meant  by  "  elastic  limit  "  with- 
out an  explanation — which  explanation  is  not  usually  given. 

The  relatively  large  space  given  to  the  subject  of  timber  is  not  more  than 
its  importance  as  a  structural  material,  and  the  general  absence  of  scientific 
information  on  the  subject  would  seem  to  demand.  Probably  the  reason 
little  has  been  given  on  this  subject  hitherto,  in  such  works  as  this,  is  because 
little  has  been  known.  Until  the  Forestry  Division  of  the  U.  S.  Agricul- 
tural Department  began  the  systematic  study  of  timber  and  timber-trees, 
some  five  or  six  years  ago,  very  little  accurate  or  scientific  information  was 
obtainable  as  to  the  mechanical  and  other  properties  of  American  timber. 
The  author's  intimate  connection  with  these  investigations  is  a  further  reason 
why  he  should  here  present  an  adequate  account  of  the  work  done  to  date.* 

It  has  been  no  part  of  the  author's  aim  to  give  working  rules  for  using 
materials  in  structures  of  various  kinds,  or  to  propose  original  specifications 
to  be  used  in  the  purchase  of  materials.  He  has  tried  to  impart  a  knowl- 
edge of  the  properties  of  materials;  on  what  these  depend;  the  ordinary 
causes  of  variation  and  defects,  and  how  these  should  be  discovered;  thus 
making  the  reader  competent  to  draw  his  own  specifications  and  to  make  his 
own  rules. 

The  latest  forms  of  investigation  of  metals  and  building-stones  by  means 
of  the  microscope  are  briefly  treated  (the  former  in  Appendix  B) ;  and  a 
chapter  has  been  given  on  the  magnetic  properties  of  iron  and  steel,  and  the 
methods  to  be  employed  in  determining  these.  This  chapter  need  be  read 
by  electrical  students  only. 

The  author  has  acknowledged  his  sources  of  information  in  the  text,  and 
especially  in  the  legends  accompanying  the  cuts.  In  addition  to  these  he 
desires  to  make  a  special  acknowledgment  here  of  his  obligation  to  Pro- 
fessors Bauschinger,  Tetmajer,  and  Martens;  to  the  French  Commission 
Report;  and  to  Mr.  Henry  M.  Howe,  Prof.  Thomas  Turner,  Mr.  G-.  R. 
Redgrave,  Prof.  J.  Q.  Arnold,  Mr.  Thos.  Andrews,  Mr.  H.  H.  Campbell,  and 
to  Dr.  B.  E.  Fernow.  His  thanks  are  also  due  to  Dr.  Wm.  Trelease  for 
assistance  in  obtaining  illustrations  of  American  trees  in  Chap.  XIII;  to 
Mr.  II.  A.  Wheeler,  E.M.,  for  the  chapter  on  the  manufacture  of  paving- 
brick;  to  Mr.  W.  A.  Layman,  M.S.,  for  the  chapter  on  the  magnetic  prop- 
erties of  iron  and  steel;  and  to  Prof.  H.  Aug.  Hunicke,  E.M.,  for  revising 
the  manuscript  of  Chapters  VII  to  XI  inclusive. 

There  are  to-day  a  few  exceptionally  fertile  sources  of  exact  information 
on  subjects  pertaining  to  the  materials  of  construction,  prominent  among 
which  may  be  named  : 

1.  The  annual  publications  of  the  Results  of  Tests  made  at  the  U.  S. 
Arsenal,  Watertown,  Mass.,  beginning  in  1882. 


*  The  author  has  had  entire  charge  of  the  mechanical  tests,  some  40,000  of  which  have 
"been  made  in  his  laboratory  at  St.  Louis. 


Vl  PREFACE. 

2.  Bauschinger's  Communications  from  the  Laboratory  of  the  Technical 
School  at  Munich,  Germany. 

3.  Tetmajer's  Communications  from  the  Laboratory  of  the  University  at 
Zurich,  Switzerland. 

4.  Martens'  Communications  from  the  Laboratory  of  the  University  of 
Berlin,  Germany. 

5.  The  Report  of  the  French   Commission   (of  115  members)  on  the 
Standardization  of  Tests  of  the  Materials  of  Construction,  in  four  quarto 
volumes,  1895. 

6.  The  Monthly  Journal,  Baumateridlenkunde,  published  in  Zurich,  as 
the  organ  of  the  International  Society  for  the  Standardization  of  the  Tests 
of  Materials  of  Construction. 

The  entire  engineering  profession  is  so  indebted  to  the  late  Prof.  Johann 
Bauschinger  for  the  work  he  has  done  in  developing  the  scientific  testing  of 
materials  that  the  author  of  this  work  has  chosen  to  express  his  feeling  of 
gratitude  to  him  by  using  his  portrait  as  a  frontispiece  and  giving  a  brief 
account  of  his  life  in  Appendix  A. 

That  this  work  may  contribute  somewhat  towards  more  rational,  safe, 
and  economic  practices  in  the  designing  of  all  kinds  of  construction  has  been 
the  purpose  and  is  now  the  hope  of 

THE  AUTHOR. 

ST.  Louis,  Mo.,  Jan.  1897. 


TABLE  OF  CONTENTS. 


PART  I. 

SYNOPSIS  OF  THE  PRINCIPLES  OF  MECHANICS   UNDER- 
LYING   THE  LAWS   OF  THE  STRENGTH  OF 
MATERIALS. 

CHAPTER    I. 
GENERAL  NATURE   OF  DEFORMATION  AND  STRESS. 

PAGE 

Elastic  and  Plastic  Bodies— Stress  and  Deformation— Proportionality  of  Stress  and 
Deformation  inside  the  Elastic  Limits— Kinds  of  Deformation  and  Stress — 
Longitudinal  and  Lateral  Deformation  under  Direct  Stress— Angular  Defor- 
mation under  Direct  Stress— Relation  between  Shearing  and  Direct  Stresses 
— Shearing  Modulus  of  Elasticity .* 1 

CHAPTER   II. 
MATERIALS  UNDER  TENSILE  STRESS. 

General  Phenomena  accompanying  Tensile  Tests— Significant  Results  of  Tensile 
Tests — True  Elastic  Limit— Apparent  Elastic  Limit— Ultimate  Strength — 
Percentage  of  Elongation— Reduction  of  Area  of  Cross-section 10 

CHAPTER  III. 
MATERIALS   UNDER  COMPRESSIVE  STRESS. 

Two  Classes  of  Engineering  Materials — Crushing  Strength  of  Plastic  or  Viscous 
Materials— Crushing  Strength  of  Brittle  Materials— Relation .  of  Crushing 
Strength  tc  Shearing  Strength — Crushing  Strength  of  Prisms'— Relative 
Strength  of  Prisms  and  Cubes — Loading  on  a  Portion  of  Cross-section  only- 
General  Laws  of  Crushing  Strength— Strength  of  Columns— Weakening 

Effects  of  Eccentric  Loading 24 

vii 


Till  TABLE  OF  CONTENTS. 

CHAPTER  IV. 
MATERIALS   UNDER  SHEARING  STRESS. 

PAGE 

Two  Manifestations  of  Shearing  Stress — Moment  of  Torsion — Shearing  Deforma- 
tions   38 

CHAPTER  V. 
MATERIALS  UNDER  CROSS-BENDING  STRESS. 

Historical  Sketch — Fundamental  Equations  of  Equilibrium— Moment  of  Resistance 
and  Stress  on  Extreme  Fibre— Resistance  of  Beams  of  Various  Forms  of 
Cross-section — Resistance  of  Beams  beyond  their  Elastic  Limits — Distribution 
of  Stress  and  Position  of  Neutral  Axis  at  Rupture— Moduli  of  Rupture  in 
Cross-breaking — Distribution  of  Shearing  Stress  in  a  Beam— Wooden  Beams 
in  Shearing  and  Cross-bending— Deflection  of  Beams— General  Formulae — 
Various  Cases  analyzed— Table  of  Moments,  Stresses,  and  Deflections — 
Deflection  from  Shearing  Forces — Determination  of  Young's  Modulus  of 
Elasticity— Rational  Designing  of  Flitched  Beams — Steel  and  Concrete  in 
Combination — Flat  Plates  computed  approximately ". . .  42 

CHAPTER   VI. 
THE  RESILIENCE   OF  MATERIALS. 

Resilience  defined — Varieties  of — A  Measure  of  Shock-resistance — Impact  Stresses — 
Resilience  Areas  in  Stress-diagram's — Resilience  in  Direct  Stress — In  Cross- 
bending — In  Torsion — Comparative  Table 75 


PART  II. 

MANUFACTURE  AND    GENERAL  PROPERTIES   OF  THE 
MATERIALS   OF  CONSTRUCTION. 

CHAPTER  VII. 
CAST  IRON. 

General  Classification  of  Iron  and  Steel— Physical  Properties  of  Cast  Iron— Carbon 
in— Silicon  in— Remarkable  Effects  of  Silicon— Sulphur,  Phosphorus,  and 
Manganese  in— Grading  Pig  Iron— Foundry  Practice— The  Cupola— Kernel  t- 
ing— Moulds—  Moulding  Sand— Size  and  Shape— Shrinkage— Mechanical 
Properties— Hardness— Strength  in  Compression,  Tension,  and  Cross-bending 
— Malleable  Cast  Iron— Method  of  Manufacture — Mechanical  Properties 87 


TABLE  OF  CONTENTS.  ix 

CHAPTER   VIII. 
WROUGHT  IRON. 

Methods  of  Manufacture— The  Puddling-  Process— Oxidation  in  Puddling— Muck 
Bars— Reheating  and  Rolling— Repeated  Reheatings— Imperfections  in  Fin- 
ished Product— Mechanical  Properties— Crystalline  Fracture — Welding — 
Effect  of  Reduction  in  the  Rolls  on  the  Strength ; 117 

CHAPTER   IX. 
STEEL. 

Methods  of  Manufacture — Crucible  Process — Bessemer  Process— Open-hearth  Proc- 
ess—Basic and  Acid  Processes — Comparison  of  Bessemer  and  Open-hearth 
Processes — Molecular  Structure  of  Wrought  Iron  and  Steel— Structure  as 
affected  by  Heat  Treatment— Mechanical  Qualities  of  Steel — Commercial 
Classification — Quality  as  determined  by  Chemical  Composition— Influence 
of  Carbon  on  Iron — Three  States  of  Carbon  in  Iron— Change  in  the  Carbon 
at  a  Low  Yellow  Heat— Hardening  and  Tempering— Effects  of  Carbon  on 
the  Mechanical  Qualities— On  Tensile  Strength— On  Ductility — On  Compres- 
sive  Strength — Effects  of  Silicon — Of  Manganese — Manganese  Steel — Of 
Sulphur — Red -shortness — Sulphide  of  Iron  Dangerous — Of  Phosphorus — On 
Ductility — On  Strength — Hardening — Tempering — Annealing — Corrosion. . ,  133 

CHAPTER   X. 

THE  MINOR  OR  AUXILIARY  METALS   OF   CONSTRUCTION  AND 

THEIR  ALLOYS. 

Copper  —  Zinc  —  Tin —Aluminum  —  Nature  of  Metallic  Alloys — Copper-zinc-tin 
Alloys— The  Brasses — The  Bronzes— Alloyed  Aluminum — Aluminum  in 
Steel— Fusible  Alloys 172 

CHAPTER  XL 
LIME,   CEMENT,   MORTAR,   AND  CONCRETE. 

Quick,  or  Fat,  Lime — Hardening  of  Lime-mortar — Hydraulic  Lime — Natural 
Cement — Portland  Cement — Historical  Account  of — Ingredients  of— The 
Clay — Silica  and  its  Compounds — Alumina — Sulphur  Compounds — Chemical 
Reactions  in  the  Furnace — Chemical  and  Physical  Changes  in  Setting  and 
Hardening— Slag-cements — Sources  of  Raw  Materials  for  Portland  Cement — 
Processes  used  in  Pulverizing  and  Mixing — Processes  used  in  Burning- 
Grinding  the  Clinker. 181 

CHAPTER  XII. 
THE  MANUFACTURE  OF  VITRIFIED  PAVING-BRICK. 

Definition  of — Clays  employed — Physical  Properties  of  Clays — Preparation  of  the 

Clays — Moulding — Drying  and  Burning — Annealing — Sorting 196 


X  TABLE  OF  CONTENTS. 

CHAPTER   XIII. 
TIMBER. 

PAGE 

Structure  and  Appearance — Classes  of  Trees— Sapwood  and  Heartwood — Annual 
Rings — Spring  and  Summer  Wood — Anatomical  Structure  of  Broad  leaved 
Trees — Minute  Structure — Grains  of  Wood — Color  and  Odor — Resonance — 
Weight  a  Function  of  Structure  and  Moisture — Variation  of  Weight  in  Single 
Trunk  and  in  Species — Moisture  Distribution — Drying  Timber — Shrinkage 
explained— Effects  of  Shrinkage— Amount  of  Shrinkage — Mechanical  Proper- 
ties— Stiffness — Strength  as  a  Beam — In  Tension  and  Compression — In 
Shearing — Influence  of  Weight  and  Moisture  on  Strength — Hardness — 
Cleavability —  Flexibility  —  Toughness —  Practical  Conclusions  —  Chemical 
Properties  and  Technological  Products — Wood  as  a  Fuel — Charcoal  Prod- 
ucts of  Wood-distillation — Durability  and  Decay — All  Decay  produced  by  a 
Fungus-growth — Prevention  of  Decay — Structure  as  a  Key  to  Identification 
of  Species — A  Structural  Key  to  Species — Characteristic  Structural  Features 
— Use  of  the  Key — Descriptive  List  of  the  More  Important  Trees  in  the  U.  S., 
with  Illustrations  of  Leaf  and  Fruit. . ,  .205 


PAKT  III. 

TESTING-MACHINES  AND  METHODS  OF  TESTING 
MATERIALS  OF  CONSTRUCTION. 

CHAPTER  XIV. 
MECHANICAL  TESTS  IN  GENERAL. 

General  Observations— Tests  Classified— Testing-machines— Effect  of  Rate  of  Load- 
ing— Significant  Limits  of  Deformation — All  Absolute  Elastic  Limits 
unsatisfactory— The  "  Apparent  Elastic  Limit" 302 

CHAPTER   XV. 
TENSION  TESTS. 

Significance  of  Tension  Tests— Selection  of  Test  Specimens— Preparation  of  Speci- 
mens— Standard  Dimension  of  Tension-test  Specimens— Tetmajer's  Analysis 
of  the  Elongation— Time  Function  of  Tension  Tests— Tension-test  Machines 
— Gripping  Devices— Special  Machines— The  Emery  Testing-machine  fully 
Described— Exteusometers— Autographic  Diagram  Apparatus— Gauging  Im- 
plements   312 


TABLE  OF  CONTENTS.  XI 

CHAPTER    XVI. 
COMPRESSION  TESTS. 

PAGtt 

Objects  of— Compression-test  Specimens— Bedding  the  Specimen  in  the  Machine— 
Compressometers— Column  Tests— Strength  of  Column  the  same  as  its 
Apparent  Elastic  Limit— Considered  Results— Tetmajer's  Results— Formulae 
for  Strength  of  Columns— Spring  Testing-machines 353 

CHAPTER   XVII. 
CROSS-BENDING  TESTS. 

Object  of — Essential  Conditions  of — Deflection  measured  in  Testing  Cast  Iron- 
Modulus  of  Rupture— Modulus  of  Elasticity— Impact-testing  Machines 369 

CHAPTER  XVIII. 
IMPACT  AND  HARDNESS  TESTS. 

Object  of  Impact  Tests— Essential  Conditions  of — Energy  of  the  Blow— Hardness 
Denned— Test  of  Permanency  of  Form — The  Rodman  Punch  Standardized — 
Test  for  Permanency  of  Substance— Turner's  Apparatus 375 

CHAPTER   XIX. 
SHEARING  AND  TORSION  TESTS. 

Essential  Conditions  of  Shearing  Tests— Occurrence  of  Shearing  Stress  in  Practice 

— Shearing-test  Appliances — Torsion  Tests — Torsion-testing  Machines 385 

CHAPTER  XX. 
COLD  BENDING  AND   DRIFTING  TESTS. 

Significance  of  Cold-bending  Tests— Methods  of  making  them — Results  of  Cold- 
bending  and  Tension  Tests  compared — Effects  of  Punching  and  Drilling 
developed  by  Cold-bending  Tests — Combined  Specified  Requirements  in 
Tension  and  Cold-bending— Results  of  Tension,  Cold-bending,  and  Impact 
Tests  compared  — Drifting  Tests  standardized 394 

CHAPTER   XXI. 
THE  TESTING  OF  CEMENT. 

Standard  Scientific  Tests  of  Cement— Test  of  Fineness— Significance  of  Fineness- 
Thoroughness  of  Burning  tested  by  Specific-gravity  Test — Apparatus  for — 
Rate  of  Setting  Automatic  Apparatus  for  Registering — Vicat's  Needle — 


xii  TABLE  OF  CONTENTS. 

PAGE 

Tests  for  Soundness— The  Boiling  Test— Tests  of  Strength— Fixed  Relation 
between.  Tensile  and  Coin  press!  ve  Strength — Standard  Consistency  of  Neat- 
cement  Briquettes — Ell'ects  of  Varying  Percentages  of  Water— Normal  or 
Standard  Sand — Effect  of  using  Different  Sands — Consistency  of  Standard 
Mortar,  1  C  :  3  S— Formation  of  the  Briquettes— Form  of  the  Briquette— A  New 
Form  proposed — Distribution  of  Stress  over  tlie  Minimum  Section — The 
Clips — Cement  testing  Machines — Eccentricity  of  Briquette  in  Clips — Cross- 
breaking  Tests — Standard  Tests  of  Adhesion — Normal  Variations  of  Volume 
of  Cement  mortars  in  Air  and  in  "Water — Recommendations  of  the  French 
Commission  for  testing  Permanency  of  Volume — Test  of  Permeability  of 
Cement-mortar — Test  for  Decomposing  Action  of  Sea-water 407 

CHAPTER   XXII. 
TESTS  OF  THE   STRENGTH  OF  STONE   AND   BRICK. 

Crushing  Tests  of  Stone— Tests  for  Paving-brick— The  Cross-breaking  Test— The 
Crushing  Test— The  Rattler  Test  Standardized— Standard  Tests  of  Com- 
mittee of  the  National  Association  of  Brick  Manufacturers 456 

CHAPTER   XXIII. 
TESTS   OF  THE   STRENGTH  OF   TIMBER. 

Important  Deductions  from  the  U.  S.  Timber  Tests — Description  of  the  U.  S. 
Timber  Tests — Mechanical  Tests — Cross-bending  Test — Crushing-endwise 
Tests — Crushing  across  Grain  —  Shearing — Tension 462 


PART.  IV. 

THE  MECHANICAL  PROPERTIES  OF  THE  MATERIALS  OF 
CONSTRUCTION  AS  REVEALED  BY  ACTUAL  TESTS. 

CHAPTER  XXIV. 
THE  STRENGTH   OF  CAST  IRON. 

Tensile  Strength— Composition  and  Strength  of  High-grade  Cast  Iron— Compres- 
sive  Strength— Cross-breaking  Strength— Modulus  of  Elasticity— Kirkaldy's 
Results— Shrinkage  Stresses— Strength  Increased  by  Impacts— Pipes  and 
Columns  469 

CHAPTER  XXV. 
THE  STRENGTH  OF   WROUGHT   IRON. 

Strength  with  the  Grain— Strength'  across  the  Grain— Time  Function— Compressive 
Strength— Shearing  Strength— Effect  of  Stressing  beyond  the  Elastic  Limit 
— Strength  of  Chains '. 482 


TABLE  OF  CONTENTS.  xiii 

CHAPTER   XXVI. 
THE   STRENGTH   OF  STEEL. 

PAGE 

Tensile  and  Compressive  Strength— Effect  of  Varying  Percentages  of  Carbon — 
Effect  of  Thickness— Effect  of  Finishing  at  n  Low  Red  Heat— Effects  of  An- 
nealing on  Low-carbon  Steel — Tests  of  Sleel  by  Punching — Quenching  and 
.Annealing — Billet  Tests  Characteristic  of  Final  Rolled  Forms— Elongation 
and  Reduction — Compressive  Strength  same  as  the  Elastic  Limit — Elastic 
Limit  in  Compression  for  Various  Kinds  of  Contact — Areas  of  Contact  be- 
tween Wheels  and  Rails — Moduli  of  Elasticity  in  Tension  and  Compression 
— Annealing  Effects  after  Overstressiug — Effects  of  Varying  Lengths  of 
Reduced  Section — Nickel  Steel — Effects  of  Forging  and  Rolling — Steel- 
welded  Tubes— I  Beams  and  Plate  Girders — Effects  of  Stressing  beyond  the 
Elastic  Limit— Shearing  Strength— Fiictional  Resistance  of  Riveted  Joints — 
Friction  per  Square  Inch  of  Rivet  Section — Bearing  Resistance  of  Plates — 
Tensile  Strength  of  Grooved  Plates — Injurious  Effects  of  Punching  and 
Shearing — Influence  of  Form  of  Thread  on  Strength  of  Screw-bolts — Steel 
Specifications 490 

CHAPTER  XXVII. 
THE   FATIGUE  OF  METALS. 

Fatigue  Defined— Micro-flaws  in  Steel— Wohler's  Fatigue  Tests— Limits  of  Stress 
for  an  Indefinite  Number  of  Repetitious— A  New  Universal  Formula  for 
Dimensioning „ 537 

CHAPTER   XXVIII. 
STRENGTH  OF   THE   COPPER-ZINC-TIN  ALLOYS. 

Strength   of  Copper— Annealing   Copper  Wires   and   Plates— Strength  of  Brass — 

Strength  of  Bronze— Special  Bronzes 548 

CHAPTER   XXIX. 

THE  EFFECTS   OF  TEMPERATURE   ON   THE  MECHANICAL 
PROPERTIES  OF  METALS. 

Effects  on  the  Strength  of  Iron  and  Steel— The  Change  in  the  Elastic  Limit — 
Change  in  the  Modulus  of  Elasticity— Effect  on  Resistance  to  Impact- 
Effects  on  Copper  and  Bronze 557 

CHAPTER   XXX. 

RESULTS  OF  TESTS   ON  CEMENTS,  CEMENT-MORTARS, 
AND   CONCRETES. 

Strength  of  Natural  Cements— Strength  of  Portland  Cements— Modulus  of  Elas- 
ticity of  Cement-mortars — Strength  of  Sand  cement  Mortars— Variation  of 


xiv  TABLE  OF  CONTENTS. 

PAGE 

Strength  with  Increasing  Proportions  of  Sand — Variation  of  Strength  of 
Mortars  with  Varying  Size  of  Sand-grains— Relative  Economy  of  Coarse  and 
Fine  Sand-grains— Experiments  with  Sands  of  Artificial  Grauulometric  Com- 
position—Porosity of  Mortars  as  Affected  by  Size  of  Sand-grains — Effect  of 
Long  Storage  on  the  Strength  of  Cement — Effect  of  Regaugiug  after  Set 
begins — Effect  of  Carbonic-acid  Gas  on  the  Hardening  of  Cement-mortars — 
Adhesive  Strength  of  Cement-mortars— Compressive  Strength  and  Elasticity 
of  Cement  and  Concrete— Strength  and  Economy  of  Cement-mortars  and 
Concretes — Filtration  through  Concrete— Effects  of  Freezing  on  Cement-mor- 
tars and  Concretes — Anti-freezing  Mixtures — Concrete  Mixtures — Concrete 
Structures  in  Sea-water — Fire-resisting  Qualities  of  Concretes — Properties  of 
Cinder-concrete  Mixtures — Cinder-concrete  with  Expanded  Metal  Base 568 


CHAPTER   XXXI. 
RESULTS   OF  TESTS   ON   STONE  AND  BRICK. 

The  Building-stones—Weathering  of  Building-stones — Freezing  Tests — The  Sul- 
phate-of-soda  Test — Chemical  Tests— Microscopic  Tests — The  Absorption 
Test — The  Specific-gravity  Test — Compressive  Strength — Table  of  Physical 
Qualities  of  American  Building-stones — Elastic  Properties  and  Crushing 
Strength,  with  Stress-diagrams — Bauschinger's  Results — Resistance  to  Abra- 
sion—Bauschinger's  Abrasion  Tests  and  Results— Strength  and  Elastic  Prop- 
erties of  Brick  and  Brick  Piers,  with  Stress-diagrams— Results  of  Tests  of 
Paving-brick — Results  of  Tests  on  Building-brick 630 


CHAPTER  XXXII. 
EXPERIMENTAL  VALUES  OF  THE   STRENGTH  OF  TIMBER. 

The  Mechanical  Tests  of  the  U.  S.  Timber  Investigations — List  of  Species  Tested — 
Ultimate  Ends  of  the  Investigation— The  Moisture  Factor — Tables  of  Results 
on  Thirty-two  Species— Special  Investigations— Relation  between  Strength 
and  Weight— The  Factor  of  Safety— Table  of  Safe  Loads  on  Beams- 
Strength  of  Wooden  Columns— How  to  distinguish  between  Short-leaf  and 
Long- leaf  Pine  Lumber — Geographical  Distribution  of  Southern  Pines — 
Holding  Force  of  Nails 664 


CHAPTER   XXXIII. 
STRENGTH  OF  IRON  AND  STEEL  WIRE  AND  WIRE   ROPE. 

The  Strength  of  Wire— Strength  of  Steel-wire  Rope — Methods  of  Testing  the 

Strength  of  Wire  Ropes— Shop  Tests  of  Wire— The  Albert-lay  Rope 691 


TABLE  OF  CONTENTS.  XV 

CHAPTER  XXXIV. 
THE  MAGNETIC  TESTING  OF  IRON  AND   STEEL. 

PAGE 

Magnetic  Properties  defined— Hysteresis — Measurement  of  Permeability— Induc- 
tive Methods — Traction  Methods — Measurement  of  Hysteresis — Results  of 
Tests — Development  due  to  Testing — Conditions  affecting  Magnetic  Quality 
— Importance  of  Magnetic  Testing— Useful  Data  on  Conductivity 702 

APPENDICES. 

A.  BIOGRAPHICAL  SKETCH  OP  PROF.  JOHANN  BAUSCHINQER 723 

B.  STUDY  OF  IRON  AND  STEEL  BY  MICROGRAPHIC  ANALYSIS 725 

C.  COMPARATIVE  ANALYSIS  OF   THE   RESOLUTIONS  OF   THE   CONVENTIONS,  OF 

THE  FRENCH  COMMISSION,  AND  THE  AMERICAN  SOCIETY  OF  MECHANICAL 
ENGINEERS 737 

D.  STANDARD  SPECIFICATIONS  FOR  IRON  AND  STEEL..  756 


THE 
MATERIALS   OF   CONSTRUCTION. 


PART  I. 

SYNOPSIS   OF  THE  PRINCIPLES  OF  MECHANICS 

UNDERLYING    THE  LAWS   OF  THE 

STRENGTH   OF  MATERIALS* 


CHAPTER   I. 
GENERAL  NATURE   OF  DEFORMATION  AND   STRESS. 

1.  Elastic  and  Plastic  Bodies. — An  elastic  body  is  one  which,  when 
deformed  under  the  application  of  an  external  force,  will  recover  its  origi- 
nal dimensions  when  the  deforming  force  has  been  removed.  A  plastic 
body  is  one  which  will  not  recover  its  original  dimensions  after  deforma- 
tion. A  body  which  will  fully  recover  its  original  dimensions  after  defor- 
mation is  said  to  be  perfectly  elastic.  When  it  will  only  partially  recover 
its  original  dimensions  after  deformation  it  is  said  to  be  partially  elastic, 
and  to  the  extent  of  its  failure  to  recover  its  original  form  it  may  be  said 
to  be  plastic. 

All  solid  bodies  are  nearly  or  quite  perfectly  elastic  up  to  a  certain  limit 
of  deformation,  beyond  which  they  become  partly  elastic  and  partly  plastic. 
This  limit  within  which  the  body  is  nearly  or  quite  perfectly  elastic  is 
called  the  elastic  limit.  When  deformed  beyond  this  limit  the  body  will 
recover  a  portion  of  such  deformation,  the  rest  remaining  as  a  permanent 
change  or  set.  Beyond  the  elastic  limit,  therefore,  a  body  may  be  said  to 
be  partly  elastic  and  partly  plastic.  Practically  all  the  materials  used  in 
engineering  design  may  be  said  to  be  perfectly  elastic  within  certain  limits; 
and  as  these  elastic  limits  are  well  beyond  the  limit  of  maximum  loading  in 

*  This  Part  is  intended  to  be  supplementary  to  the  matter  contained  in  text-books  on 
applied  mechanics,  rather  than  to  replace  such  courses. 


2  THE  MATERIALS  OF  CONSTRUCTION. 

practice,  it  is  customary  to  regard  all  engineering  materials  as  perfectly 
elastic  for  all  practical  purposes. 

2.  Stress  and  Deformation. — The  deformation  which  a  solid  body  suffers 
on  the  application  of  an  external  force  has  commonly  been  called  strain, 
but  in  this  work  it  will  be  designated  deformation  simply.*     The  deforma- 
tion which  is  fully  recoverable  on  the  removal  of  the  external  force  may  be 
called  the  elastic  deformation.     That  which  remains  as  a  permanent  set 
after  the  external  force  has  been  removed  may  be  called  the  plastic  defor- 
mation.    Within  t.he  elastic  limit  the  deformation  is  wholly  elastic. 

The  relative  deformation  is  the  proportionate  distortion,  or  the  linear 
change  divided  by  the  original  length  or  dimension  in  the  direction  of  the 
deforming  force.  Thus  if  a  bar  10  inches  long  be  stretched  0.01  inch, 
then  this  0.01  inch  is  the  deformation,  and  the  relative  deformation  is  0.01 
divided  by  10,  or  0.001  main.  Thus  the  actual  deformation  is  a  concrete 
quantity,  and  is  measured  in  units  of  length,  while  the  relative  deformation 
is  an  abstract  number,  and  may  be  defined  as  the  ratio  of  the  distortion  to 
the  original  length.  This  relative  or  proportionate  deformation  may  also 
be  defined  as  the  deformation  per  unit  of  length. 

Stress  may  be  defined  as  the  resistance  a  solid  body  offers  to  the  defor- 
mation produced  in  it  by  the  action  of  an  external  force,  and  it  may  also  be 
defined  as  the  resistance  to  this  external  force  directly.  Under  the  law 
that  action  and  reaction  are  equal,  the  stress  must  be  quantitatively  equal 
to  the  external  force,  and  it  may  be  regarded  as  resisting  this  external 
force,  or  these  two  may  be  regarded  as  being  in  equilibrium.  Since  the 
application  of  an  external  force  to  a  solid  body,  however,  is  always  accom- 
panied by  a  deformation  of  that  body,  and  since  this  deformation  disap- 
pears on  the  removal  of  the  external  force,  the  internal  stress  in  the  body 
may  be  said  to  be  developed  as  a  resistance  to  this  deformation,  and  in  this 
sense  the  deformation  may  be  regarded  as  the  immediate  cause  of  the  stress, 
the  ultimate  cause  being  the  external  force. 

3.  Proportionality  of  Stress  and  Deformation  Inside  the  Elastic  Limit.— 
Within  the  limits  of  perfect  elasticity  of  solid  bodies  the  deformation  is 
directly  proportional  to  the  external  force  producing  that  change  of  form; 
and  since  the  internal  stress  is  of  necessity  equal  to  the  external  force,  we 
arrive  at  this  important  proposition :  Inside  the  elastic  limit  the  stress  is 
directly  proportional   to   the   deformation   ivhich   accompanies   it.\     This 

*  The  word  strain  is  used  in  common  language  in  several  other  senses,  so  that  its  use 
in  this  specific  scientific  sense,  though  warranted,  is  of  doubtful  propriety.  The  author 
has  so  used  it,  however,  in  his  previous  works. 

f  This  law  was  first  announced  by  Robert  Hooke  in  1676,  in  the  form  of  an  anagram, 
as  "  The  true  theory  of  elasticity  or  springiness  ceiiinosssttuv."  Two  years  later  the 
key  to  this  anagram  was  given  in  the  Latin  phrase  "Ut  tensio  sic  vis,"  a  free  rendering 
of  which  would  be,  "As  the  extension  so  is  the  strength."  This  law  of  proportion- 
ality, therefore,  between  the  stress  and  the  deformation  within  the  elastic  limit  is  fre- 
quently referred  to  as  Hooke's  Law. 


GENERAL  NATURE  OF  DEFORMATION  AND  STRESS.  3 

proposition  may  be  stated  in  another  way  by  saying  that  inside  the  elastic 
limit  the  stress  per  unit  area  divided  by  the  proportional  deformation  is  a 
constant  for  any  particular  solid  body.  Since  this  constant  is  the  ratio  of 
the  deforming  force  to  the  accompanying  deformation  of  any  particular 
solid  body,  it  is  evidently  an  important  function,  and  it  has  therefore  been 
given  a  name.  The  name  of  this  ratio  is  the  modulus  of  elasticity.  We 
have,  therefore, 


Modulus  of  elasticity  =  E  =  -=—  —    —-.  —  -,   .     .     .     .     (1) 

deformation 

wherein  by  stress  is  meant  stress  in  pounds  per  square  inch,  and  by  defor- 
mation is  meant  a  proportionate  change,  or  the  deformation  per  unit  of 
length.  Thus  if  an  external  pull,  P,  be  applied  to  a  bar  whose  cross-section 

p 
is  Ay  then  the  unit  stress  is  —  ;  and  if  the  length  of  the  bar  be  I,  and  its 

actual  extension  under  the  application  of  this  external  force  be  a,  then  the 

deformation,  or  proportionate  distortion,  would  be  y,  whence  we  should  have 

t 


a        Aa       a"* 
7 

wherein  p  is  the  stress  in  pounds  per  square  inch.  Thus  if  the  external 
force  of  60,000  pounds  be  applied  to  a  bar  whose  length  is  10  inches  and 
whose  cross-section  is  2  square  inches,  and  if  the  extension  under  this  load 
be  0.01  inch,  we  should  have 


That  is  to  say,  such  a  material  would  have  a  modulus  of  elasticity  of 
30,000,000;  and  this  is  about  the  average  value  of  the  modulus  of  elasticity 
of  steel. 

Example. — If  steel  rails  be  welded  together  at  a  temperature  of  80°  F.,  what 
will  be  the  total  tensile  stress  in  an  80-pound  rail  at  a  temperature  of  20°  below 
zero,  and  what  will  be  the  compressive  stress  in  this  rail  at  a  temperature  of  140°  F., 
the  coefficient  of  expansion  being  assumed  as  0.0000065  per  degree  F.? 

In  solving  such  a  problem  as  this,  since  the  length  of  the  rail  cannot 
change  for  a  change  of  temperature,  the  contraction  which  would  occur  if  free 
to  move  is  overcome  by  the  application  of  a  sufficient  external  force  coming 
from  the  surrounding  bodies  to  prevent  this  contraction.  In  other  words, 
an  external  force  is  developed  just  sufficient  to  stretch  the  body  as  much  as 
it  would  contract  under  a  fall  of  temperature,  and  similarly  an  external 
force  is  exerted  to  compress  the  body  as  much  as  it  would  expand  under  a 


4  THE  MATERIALS  OF  CONSTRUCTION. 

rise  of  temperature.  We  have  then  only  to  determine  the  amount  of  the 
contraction  or  expansion  from  temperature  and  call  this  the  deformation 
produced  by  the  application  of  an  external  force,  and  then  by  the  aid  of  the 
modulus  of  elasticity  find  the  amount  of  this  external  force,  and  divide  it  by 
the  area  of  the  cross-section  of  the  rail,  thus  obtaining  the  internal  stress  in 
pounds  per  square  inch.  The  cross-section  of  the  rail  is  indicated  by  its 
weight.  The  weight  of  rails  is  always  given  in  pounds  per  yard,  and  it  so 
happens  that  a  bar  of  iron  or  steel  one  inch  square  and  36  inches  long 
weighs  just  ten  pounds.  This  unit  is  called  an  inch-yard.  Therefore  an 
80-pound  rail  has  just  eight  inches  of  cross-section.  With  the  above 
information  the  student  is  prepared  to  solve  the  problem.  It  is  evident  that 
the  length  need  not  be  considered;  or  any  length  may  be  chosen,  as,  for 
instance,  one  inch,  since  only  the  proportionate  change  of  length  need  be 
considered  in  either  case.  The  answers  to  the  problem  are  156,000  pounds 
total  stress  in  tension  at  the  lower  temperature  and  93,600  pounds  total  stress 
in  compression  at  the  upper  temperature,  the  stress  per  square  inch  being 
19,500  pounds  in  tension  and  11,700  pounds  in  compression,  respectively. 
Since  the  elastic  limit  in  both  tension  and  compression  of  this  grade  of  steel 
is  about  45,000  pounds  per  square  inch,  it  is  evident  that  these  stresses  are 
well  within  these  elastic  limits,  and  hence  no  injury  to  the  rail  would  ensue 
from  the  prevention  of  expansion  and  contraction  in  this  manner. 

4.  Different  Kinds  of  Deformation  and  Stress. — Under  the  application  of 
suitable  external  forces  there  are  commonly  recognized  five  kinds  of  defor- 
mation, namely:  Extension,  Compression,  Angular,  Bending,  and  Twisting; 
and  corresponding  with  these  are  five  kinds  of  stress,  namely:  Tensile, 
Compressive,  Shearing,  Bending,  and  Tortional.  The  last  two  kinds  of 
stress  are  really  combinations  of  the  other  three.  Thus,  bending  stress  may 
be  resolved  into  tension  and  compression,  with  or  without  shearing,  and  a 
tortional  stress  is  a  particular  kind  of  shearing  stress.  For  any  particular 
kind  of  material  there  is  a  definite  relation  between  these  several  deforma- 
tions and  their  corresponding  stresses.  The  numerical  values  of  the  ratios 
of  these  corresponding  deformations  and  stresses  are  the  moduli  of  elasticity 
in  the  several  cases.  It  so  happens,  however,  that  the  modulus  of  elasticity. 
or  the  ratio  between  the  stress  and  the  deformation  in  tension,  is  usually  the 
same  as  it  is  in  compression.  Both  tension  and  compression  are  called  direct 
stresses,  and  hence  we  may  in  general  speak  of  the  modulus  of  elasticity  in 
direct  stress,  and  the  modulus  of  elasticity  in  shearing,  in  cross-bending,  and 
in  torsion.  Since  cross-bending  distortion  gives  rise  mostly  to  distortion 
in  extension  and  compression,  and  their  corresponding  stresses,  the  modulus 
of  elasticity  in  cross-bending  may  also  be  said  to  be  the  same  as  that  in 
direct  stress. 

The  modulus  of  elasticity,  therefore,  which  is  used  in  tension,  compres- 
sion, and  cross -bending,  is  one  and  the  same,  and  is  sometimes  spoken  of  as 
Young's  modulus.  That  is  to  say,  it  is  the  ratio  between  direct  stress  in 


GENERAL  NATURE  OF  DEFORMATION  AND  STRESS.  5 

pounds  per  square  inch  and  the  corresponding  proportionate  linear  defor- 
mation. 

5.  Longitudinal  and  Lateral  Deformation  under  Direct  Stress. — The  lon- 
gitudinal deformation  of  a  solid  body  in  the  direction  of  the  deforming  force 
is  A/,  where  I  is  the  original  length  in  this  direction  and  A  is  the  proportion- 
ate deformation.  Hence  we  may  write,  for  Young's  modulus, 

_          stress  per  unit  area          _  p 

deformation  per  unit  length       A*  ^  ' 

It  is  a  fact  of  observation  that  when  a  metal  body  is  elongated  by  an  exter- 
nal force  from  ltol-\-\l  (inside  the  elastic  limit),  it  contracts  laterally  about 
one  fourth  of  its  proportionate  elongation.  Hence  if  the  original  diameter 

were  d,  its  diameter  after  stretching  would  be  d  —  -d.    This  ratio  of  lateral 

4) 

to  longitudinal  deformation.,  under  longitudinal  external  forces,  is  called 
Poisson's  ratio.  It  is  usually  taken  as  J-  for  all  metals,  but  for  india-rubber 
it  is  J.  The  true  values  of  this  ratio,  for  some  of  the  more  common  mate- 
rials, are :  * 


Glass  ....  0.2451 
Steel  ....  0.2686 
Copper  .  .  .  0.3270 


Brass 0.3275 

Delta-metal     ....     0.3399 
Lead  0.4282 


6.  Change  of  Volume  under  Direct  Stress.—  If  the  length  of  the  body  is 
incfeased  by  \l,  and  its  lateral  dimensions  are  decreased  by  jAfZ,  the  new 
volume  for  a  rectangular  bar  having  lateral  dimensions  of  b  and  d  would  be 


But  the  original  volume  was  Ibd,  hence  the  change  of  volume  is  Ibd- 

2 

and  the  relative  change  is  Ibd—  divided  by  the  original  volume  =  -,  or  the 

*  & 

volume  has  been  increased  by  one  half  as  great  a  percentage  as  the  length 
was  increased. 

If  we  should  now  apply  an  equal  direct  tension  in  the  direction  of  b,  we 

would  increase  this  dimension  by  A#,  and  the  volume  by  -J,bd9  and  similarly 
for  a  tensile  force  in  the  direction  of  d.     Hence  for  a  direct  tensile  force  in 

*  Taken  from  Wertheim  and  given  in  the  Report  of  the  French  Commission  des 
MetJtodes  d'Essai  des  Materiaux  de  Construction,  1895,  vol.  in.  p.  6. 

f  Since  A  is  very  small  as  compared  to  unity.  The  product  of  (I  -f-  m)(l  -f-  ri)(l  -f-  p), 
etc.,  where  m,  n,  and  p  are  very  small  fractions,  is  I  -f-  (m  +  n  -f  p),  since  the  products 
of  the  auxiliary  terms  can  be  neglected. 


G 


THE  MATERIALS  OF  CONSTRUCTION. 


all  three  planes  the  volume  would  be  increased  by  |A  times  its  original  vol- 
ume, and  each  dimension  by  -J/\  times  its  original  measure. 

For  a  compressive  force  in  all  directions  the  volume  would  be  diminished 
to  (1  —  |  A,)  times  its  original  volume,  and  each  lineal  dimension  to  (1  —  JA) 
times  its  original  measure.. 

The  volumetric  change  of  a  solid  body  for  an  equal  stress  applied  in  all 
directions  is  therefore  f  of  the  change  of  the  dimension  in  the  direction  of 
an  equal  simple  longitudinal  stress.  Thus  the  longitudinal  proportionate 
deformation  for  a  direct  stress  of  p  pounds  per  square  inch  is  A,  or 


-But  since  the  relative  volumetric  change  for  stress  in  all  directions  is 
f  A,  we  have  as  the  ratio  between  volumetric  stress  and  deformation  under 
an  equal  stress  in  all  directions,  as  a  fluid  pressure  for  instance, 


whence 


=    E. 


That  is  to  say,  the  volumetric  modulus  of  elasticity  of  a  solid  body  for  an 
equal  stress  in  all  directions  is  f  of  Young's  modulus,  which  applies  only  to 
direct  stress  in  one  plane  and  its  accompanying  deformation.* 

7.  Angular  Deformation  under  Direct  Stress. — We  will  here  consider  one 

case  only  of  angular  deformation  under 
direct  stress,  and  that  is  for  equal  di- 
rect stresses  of  opposite  signs  on  planes 
at  right  angles  to  each  other,  as  shown 
in  Fig.  1.  If  the  original  length  of 
each  side  of  this  cube  be  /,  then  the 
dimension  in  the  direction  of  l^  will  be 
increased  as  much  by  the  action  of  the 
vertical  compression  V  as  it  will  be 
diminished  by  the  action  of  the  hori- 
zontal tension  H,  since  V  =  H  in 
pounds  per  square  inch.  Also  the 
cube  will  be  shortened  in  the  direction  /3  by  an  amount  XI  due  to  the  force 

*  This  statement  applies  only  to  bodies  in  which  Poisson's  ratio  is  £.  Since  this 
ratio  is  very  nearly  •£  for  india-rubber,  it  follows  that  the  cross-section  is  reduced  as 
much  as  the  length  is  increased,  under  a  tensile  stress  m  one  plane,  and  hence  the 
volume  remains  unchanged.  Similarly,  for  a  compressive  stress  in  all  directions  the 
volume  is  unchanged  (almost);  so  that  while  Young's  modulus  of  elasticity  for  this 
material  is  very  small,  the  volumetric  modulus  is  very  great:  and  if  Poisson's  ratio  were 
quite  \,  the  volumetric  modulus  would  be  infinite,  or  it  would  tje  quite  incompressible. 
It  is  probably  the  most  incompressible  of  any  known  substance. 


GENERAL  NATURE  OF  DEFORMATION  AND  STRESS.  7 

V,  and  by  J-  this  amount  due  to  the  lateral  force  H.  Also  the  dimension  in 
the  direction  £,  will  be  elongated  by  A£  from  the  action  of  the  horizontal 
force  H,  and  by  £  this  amount  from  the  force  F.  Hence  the  final  dimen- 
sions in  these  directions  will  be  1(1  —  |A)  and  1(1  -j-  H)  respectively. 

If  in  the  front  face  of  this  cube  the  lines  ABGD  be  drawn,  joining  the 
middle  points  of  the  edges  before  deformation,  this  figure  is  a  square.  After 
deformation,  if  we  make  the  point  at  A  common  to  the  two  figures,  we 
have  the  points  B,  C,  and  D  moved  to  B',  C',  and  D'  respectively.  This 
produces  an  angular  movement  of  one  of  these  lines  equal  to  the  angle 
BAB'  ,  which  we  will  call  6.  This  is  now  one  half  the  deviation  of  the 
angles  B'AD',  B'C'D',  AB'C',  and  AD'  Q'  from  right  angles. 

But  since  BG  —  GBf  =  J(J  A/),  we  may  assume  that  B'  falls  on  BC, 
since  0  is  very  small. 

Also, 


BB'      ,,  .    .BG 

tan  0  =  —  —  =  (from  similar  triangles)  —r-=,  =  *   .  '•       =  f  A. 

-?>(/ 


Or,  since  6  is  small,  we  may  say, 

6  =  f  A,  where  0  is  given  as  arc  in  terms  of  the  radius  as  unity. 
But  8  =  J  the  deviation  of  the  angles  AB'C',  B'C'D',  etc.,  from  right 
angles.     Hence  we  have 

20  =  angular  change  =  2(f  A)      ......     (5) 

equals  twice  the  linear  deformation. 

That  is  to  say,  two  direct  stresses  at  right  angles  to  each  other  and  of 
opposite  signs  produce  in  the  plane  of  the  stresses  an  angulnr  deformation 
equal  to  twice  the  proportionate  linear  deformation.  This  result  will  be 
used  in  Art.  9  in  obtaining  the  ratio  of  the  modulus  of  elasticity  in  shearing 
to  that  in  direct  stress. 

8.  Relation  between  Shearing  and  Direct  Stresses.  —  In  Fig.  2  let  the 
square  ABGD  represent  a  very  small  portion 
of  a  longitudinal  section  of  a  body,  taken  in 
the  plane  of  the  forces.  Assume  also  that 
there  are  shearing  forces  acting  on  the  body, 
which  have  developed  at  this  point  in  this 
plane  a  shearing  stress  on  the  vertical  sides  / 

equal  to  s,  pounds  per  square  inch,  these 
forming  a  couple  and  producing  a  turning 
moment.  Evidently  this  particle  can  only 
be  held  from  turning  in  this  plane  by  the 
development  of  an  exactly  equal  shearing 
stress  (or  resistance)  on  the  horizontal  faces,  „ 

which  will  give  an  opposing  couple  and 
moment  of  resistance  equal  to  the  turning  moment  of  the  origina.  shearing 


s, 


8  THE  MATERIALS  OF  CONSTRUCTION. 

forces.  If  the  lengths  of  these  sides  be  equal,  we  shall  then  have  sa  =  s1  ir 
pounds  per  square  inch.  Hence  we  may  say: 

A  shearing  stress  in  one  direction  at  any  point  in  a  body  develops  an 
equal  opposing  shearing  stress  at  right  angles  to  it  in  the  plane  of  the 
resultant  external  forces. 

But  the  two  sets  of  shearing  forces  indicated  in  the  figure  will  tend  to 
deform  the  body  by  elongating  it  in  the  direction  BD,  and  shortening  it  in 
the  direction  AC.  The  internal  resistance  to  such  a  deformation  develops 
in  the  body  a  direct  tensile  stress  or  resistance  along  the  line  A  C  and  a 
compressive  stress  along  the  line  BD. 

If  Sl  =  $2  represent  the  total  shearing  stresses  on  the  vertical  and  hori- 
zontal sides  of  this  particle,  respectively  (s,  and  *,  being  equal  intensities  of 
stress,  or  stress  in  pounds  per  square  inch),  then  we  may  resolve  these  along 
the  diagonals  and  obtain 

total  tensile  stress  on  AC  =  Vs*  +  S9*  =  Vs'33*  +  8 

=  sAC=  T 


=  total  compressive  stress  on  BD  —      S?  -j-  S*  =  (?, 

or  these  two  direct  stresses  also  are  equal. 

But  the  stress  per  square  inch  is  the  total  stress  divided  by  the  area 
over  which  it  acts;  hence  AVC  have  for  the  intensities  of  the  tensile  and 
compressive  stresses 


Hence  we  have  the  larger  conclusion  that 

A  shearing  stress  in  one  direction  at  any  point  in  a  body  develops  an 
equal  opposing  shearing  stress  at  right  angles  to  it  in  the  plane  of  the  exter- 
nal forces,  and  these  opposing  shearing  stresses  produce  two  opposing  direct 
stresses  'acting  at  45°  with  the  shearing  stresses  and  at  right  angles  to  each 
other,  these  tensile  and  compressive  stresses  having  the  same  intensities,  in 
pounds  per  square  inch,  as  the  original  shearing  stress. 

9.  The  Shearing  Modulus  of  Elasticity.  —  The  modulus  of  elasticity  in 
shearing  may  be  defined  as  the  ratio  of  the  shearing  stress  in  pounds  per 
square  inch  to  the  accompanying  angular  deformation.  By  angular 
deformation  is  here  meant  the  angular  change,  as  derived  in  Art.  7,  where 
20  is  a  pure  ratio,  being  the  ratio  of  arc  to  radius.  From  the  last  article 
we  know  that  a  shearing  stress  gives  rise  to  direct  stresses  at  right  angles  to 
each  other,  of  opposite  signs,  but  of  equal  intensities;  and  when  such  stresses 
act,  we  learned  in  Art.  8  that  the  proportionate  angular  change  was  twice 
the  proportionate  linear  change  when  equal  direct  stresses  were  acting  at 
right  angles  to  each  other.  But  when  both  of  these  stresses  were  acting 
we  found  the  linear  change  to  be  f  A,  or  f  that  due  only  to  the  deforming 


GENERAL  NATURE  OF  DEFORMATION  AND  STRESS.  9 

force  in  that  direction;  and,  as  found  in  equation  (5),  20  —  2(fl),  we  have 

26  =  f  A. 

But  E  =  Young's  modulus  of  elasticity  —  j-, 

o 

and  E8  —  shearing  modulus  of  elasticity  —  ~^ 

_  shearing  stress  per  square  inch 
angular  deformation 

But  we  have  shown,  when  s  =  p,  20  =  f  A,;  hence  we  have 


That  is  to  say,  Es  =  \E,  or  ^e  shearing  modulus  of  elasticity  =  f  of  the 
linear  or  Young's  modulus.* 

*  This  conclusion  is  based  on  a  value  of  Poisson's  ratio  of  £.     The  general  relation 
between  Es  and  E  is  Es  =  —  h  =  -  —  r~\^  where  m  is  the  reciprocal  of  Poisson's  ratio. 

Z'J         ,i  771  -f-  1 

Thus  if  this  ratio  be  i,  which  it  is  approximately  for  brass  and  copper,  then  m  =  3  and 
Es  =  %E,  while  for  india-rubber,  where  m  =  2,  we  have  Es  =  ^E.  Prof.  Bauschiuger's 
tests  on  round  bars  of  steel  give  Es  =  13,600,000,  while  for  square  bars  of  the  same 
s  material  he  found  Es  =  11,500,000,  thus  showing  a  failure  of  the  theory  to  harmonize 
results  on  these  two  forms  of  cross-section  even  inside  the  elastic  limit.  See  Rep. 
French  Commission,  vol.  m.  p.  208,  for  Bauschinger's  results. 


CHAPTER  II. 
MATERIALS  UNDER  TENSILE   STRESS. 

10.  General  Phenomena  accompanying  Tensile  Tests. — When  a  body  of 
uniform  cross-section  is  subjected  to  the  action  of  an  external  force  which 
tends  to  pull  it  asunder,  it  is  elongated  in  the  direction  of  this  force  by  a 
proportionate  amount  equal  to  the  average  force  per  square  inch  divided 
by  its  modulus  of  elasticity;  thus 

A  =  the  proportionate  elongation  =  ^, 

where  p  is  the  external  force,  or  internal  stress,  in  pounds  per  square  inch, 
and  E  is  the  modulus  of  elasticity  (Young's  modulus). 

At  the  same  time  its  lateral  dimensions  are  reduced  by  one  fourth  as 
great  a  percentage  as  that  which  represents  the  proportionate  elongation,  as 
described  in  Art.  5.  This  rate  of  elongation  in  the  direction  of  the  force, 
and  contraction  in  its  transverse  dimensions,  continues  in  strict  proportion 
to  the  amount  of  the  external  force,  until  the  elastic  limit  is  reached,  when 
both  the  longitudinal  elongation  and  the  transverse  contraction  begin  to 
increase  at  a  more  rapid  rate,  until  finally,  with  the  more  ductile  metals, 
the  condition  of  perfect  plasticity  or  viscosity  is  reached,  and  the  body 
elongates  under  a  constant  force,  while  the  lateral  dimensions  reduce  more 
and  more,  until  rupture  finally  occurs. 

If  the  external  force  or  load,  in  pounds  per  square  inch,  be  represented 
by  vertical  ordinates,  and  the  corresponding  elongations  be  represented  by 
horizontal  abscissae,  then  the  action  of  the  specimen  under  test  may  be 
indicated  by  what  is  known  as  a  stress-diagram,  the  vertical  coordinates 
representing  stress,  and  the  horizontal  coordinates  the  corresponding  defor- 
mations. In  Fig.  3  such  stress-diagrams  are  shown  for  timber,  ca3t  iron, 
wrought  iron,  and  steel.  These  lie  on  the  upper  side  of  the  horizontal 
axis.  If  the  same  materials  were  to  be  subjected  to  compressive  external 
forces,  corresponding  stress-diagrams  might  be  drawn  in  opposite  direc- 
tions, that  is  to  say,  downward  and  to  the  left,  as  indicated  in  Fig.  3,  below 
the  horizontal  axis. 

In  a  complete  stress-diagram  of  a  ductile  metal  there  are  four  signifi- 
cant points  which  need  to  be  noted.  These  are:  the  true  elastic  limit, 
the  apparent  elastic  limit,  the  ultimate  strength,  and  the  breaking-point* 

10 


MATERIALS   UNDER  TENSILE  STRESS. 


11 


These  four  significant  points  in  a  tension  stress-diagram  are  indicated  by 
the  letters  A,  B,  C,  and  D  in  Fig.  4,  where  the  same  diagram  is  drawn  to 
widely  different  horizontal  scales. 

Thus  the  point  A  is  the  true  elastic  limit,  or  the  ratio  of  the  stress  to 
the  deformation  is  a  constant  from  the  origin  to  this  point.  This  requires 
that  the  stress-diagram  should  be  a  perfectly  straight  line  from  0  to  A. 
Beyond  the  elastic  limit,  or  above  A,  the  deformation  sometimes  increases 
somewhat  more  rapidly  than  it  did  belew  A,  and  the  locus  then  becomes 
somewhat  curved  from  A  to  B.  At  B  a  very  marked  change  occurs  in  the 


FIG.  3. — Typical  Stress-diagrams  of  Timber,  Cast  Iron,  Wrought  Iron.,  and  Steel  in 
Tension  and  Compression,  drawn  to  the  same  scales. 

specimen  in  the  case  of  wrought  iron  and  structural  steel.  If  the  test  be 
continued  slowly  at  this  point,  it  will  be  found  with  the  more  ductile 
metals  that  the  specimen  elongates  a  considerable  amount  under  a  nearly 
constant  load,  as  shown  in  the  diagram,  from  B  to  B' .  This  point  is 
called  the  "  apparent  elastic  limit,"  or  the  "  yield-point "  or  the  "  breaking- 
down  point."  In  ordinary  commercial  testing  of.  iron  and  steel  this  point 
is  always  called  the  "  elastic  limit;"  and  the  true  elastic  limit,  or  the  point 
A,  is  not  found.  This  results  from  the  rapid  and  somewhat  crude  methods 


12 


THE  MATERIALS  OF  CONSTRUCTION. 


used  in  making  commercial  tests,  and  the  author  of  this  work  has  some- 
times called  this  "  apparent  elastic  limit "  the  "  commercial  elastic  limit," 
since  it  is  the  so-called  "  elastic  limit "  found  in  practically  all  the  tests 
made  by  American  inspection  bureaus  and  rolling-mills.  Since  this  yield  - 
point  has  been  so  long  regarded  as  the  "elastic  limit,"  whereas  the  point 
A  is  the  true  elastic  limit,  persons  who  wish  to  be  accurate  and  at  the  same 


SCALE  FOR  MAGNIFIED  DEFORMATION 

005  0.1  0.15  0.2  0.25 


JO*  15*  20# 

DEFORMATION 

FIG.  4. 


25% 


time  to  be  understood  find  difficulty  in  conveying  their  meaning.*  The 
terms  "yield-point"  and  "breaking-down  point"  are  not  in  common  use, 
while  the  term  "  elastic  limit "  is  commonly  misused.  In  the  present  state 
of  knowledge  on  the  subject,  therefore,  the  terms  "  true  elastic  limit "  and 
"  apparent  elastic  limit "  probably  would  best  describe  the  points  A  and  B 
respectively.!  It  has  been  the  practice  of  the  author,  in  making  tests  to 
be  used  commercially,  to  call  the  point  B  the  "  elastic  limit,"  without  any 
explanation  or  exception,  when  he  desired  his  results  to  be  comparable 
with  those  made  elsewhere  for  commercial  purposes. 

Just  what  happens  to  the  specimen  at  the  point  B  is  well  shown  on 
Plate  I,  I  which  is  a  reproduction  of  a  photograph  of  specimens  of  polished 

*  Fortunately,  in  the  case  of  soft,  or  structural,  steel  these  true  points  are  practically 
identical,  so  that  in  this  material  no  such  distinction  of  terms  as  is  here  proposed  are 
necessary.  See  Figs.  5,  6,  7,  and  8. 

f  The  French  Commission  use  this  term  "  apparent  elastic  limit "  for  the  point  B. 

j  The  author  has  not  seen  elsewhere  as  clear  indications  of  the  action  of  such  ma- 
terials M  the  ."yield-point."  The  tests  shown  on  Plate  I  were  made  by  him  and  photo- 
graphed  in  March,  1892.  The  bars  were  polished  to  a  mirror  surface  before  testing. 
These  photographs  were  exhibited  at  the  Engineering  headquarters  at  the  World's  Fair, 
€hicago,  1893,  and  while  they  were  much  observed  and  studied,  it  did  not  appear  that 
^ny  one  had  ever  seen  such  clear  "  breaking-down  "  indications  before.  The  significant 
fact  is  that  these  effects  come  instantly,  as  to  any  particular  marking,  and  that  they  sue- 


PLATE   I. 


PHOTOGRAPHS  OF  A  POLISHED  STEEL  BAR,  1  IN.  x  2  IN.,  AFTER  BENDING  AND  AFTER 

PULLING,  SHOWING  THE  "  BREAKING  DOWN  "  OF  THE  METAL. 
The  tensile   test  was   interrupted   before  the  breaking-down    action  had  extended 
entirely  throughout  the  length  of  the  bar.     (Tested  and  photographed  by  the  author, 
1892.) 


MATERIALS   UNDER  TENSILE  STRESS. 


steel  subjected  respectively  to  a  uniform  bending  moment  and  to  a  tensile 
stress.  This  photographic  reproduction  shows  how  the  tension  specimen 
fails  or  "  breaks  down  "  its  molecular  arrangement  in  detail  by  shearing  on 
inclined  sections,  beginning  at  the  end  of  the  specimen  where  it  was  held 


a/si 


0        0.S0M-    /.00 

FIG.  5. — Autographic  Stress- diagrams  of  Mild  Steel,  taken  simultaneously  with  the 
Gray  Exteusometer  Apparatus.     Time,  %^  minutes. 

by  the  grips.  The  breaking  down  proceeded  from  the  ends  towards  the 
centre.  In  this  case  the  test  was  stopped  before  it  had  reached  the  middle 
portion.  This  central  portion,  therefore,  is  in  its  original  or  normal  con- 
dition, while  the  remaining  portions  have  been  broken  down  in  an  irregular 

ceed  each  other  regularly  along  the  bar,  like  the  formation  of  ice-crystals  on  freezing 
water.  The  markings  on  the  tension  bar,  or  on  the  tension  side  of  a  beam,  are  depres- 
sions, while  on  a  compression  bar,  or  on  the"  compression  side  of  a  beam,  they  are 
swellings. 


14 


THE  MATERIALS  OF  CONSTRUCTION. 


weblike  pattern.  If  the  test  had  been  continued,  this  action  would  have 
gone  on  from  the  ends  towards  the  centre,  until  the  entire  specimen  had 
yielded  in  this  manner;  and  when  this  breaking-down  action  had  developed 
over  the  entire  length  o|  the  specimen,  the  point  B'  in  the  diagram  would 
have  been  reached.  This  breaking-down  action,  therefore,  all  occurs  over 


40000 


340001 


20,000 


v/rr/ 


'MT/CW 


at          as 


0.3 


FIG.  6.— Typical  Stress-diagram  of  Mild  Steel,  plotted  to  two  scales.     (From 
records  of  Tests  of  Metals,  Wat.  Ars.,  1886.) 

the  entire  length  of  the  specimen  between  the  points  B  and  B',  and  the 
reason  why  B  stands  above  B'  seems  to  be  that  it  requires  a  greater  force  to 
start  this  breaking-down  action  than  is  necessary  to  continue  it  and  extend 
it  throughout  the  length  of  the  specimen  after  it  has  once  been  started. 
See  Figs.  5,  6,  7,  and  8.  In  Figs.  7  and  8  the  true  elastic  limit  is  well 
above  the  yielding  resistance  of  the  metal,  or  the  point  A  is  above  B. 


MATERIALS   UNDER  TENSILE  STRESS. 


15 


PlG.  7.— Tensiou  Tests  of  Wrought-iron  Shafts  1  in.  in  diam.,  used  for  endurance  testSc 
Average  ultimate  strength  =  50,400  Ibs.  per  sq.  in.;  average  elongation  —  27$  on  a 
length  of  11  diameters.  (  Wat.  Ars.  Rep.,  1890.) 


16  THE  MATERIALS  OF  CONSTRUCTION. 

After  this  breaking-down  action  has  extended  over  the  entire  length  of 
the  specimen,  a  further  increase  in  the  load  will  continue  to  stretch  the 
specimen  nearly  uniformly  throughout  its  length,  with  a  uniform  reduction 


in  cross-section,  until  at  last  thf  elongation  and  reduction  continue  under  a 
constant  load.  That  is  to  say,  the  stress-diagram  becomes  horizontal  at  the 
point  C,  Fig.  4.  This  marks  the  load  under  which  the  material  is  perfectly 
plastic  or  viscous,  or  for  which  the  distortion  continues  with  no  increase  of 
load. 


MATERIALS   UNDER  TENSILE  STRESS.  17 

After  passing  the  point  C  the  specimen  begins  to  show  the  marked 
reduction  of  cross-section  at  a  particular  point,  which  will  ultimately  be 
the  plane  of  rupture.  This  action  is  indicated  in  Fig.  10.  As  soon  as  this 
"necking-down"  begins,  the  elongation  continues  under  a  diminishing 
load,  as  shown  by  the  dropping  of  the  locus  in  the  stress-diagram,  and  the 
remaining  portion  of  the  elongation  of  the  specimen  nearly  all  occurs  in 
this  immediate  vicinity.  The  area  of  cross-section  becomes  less  and  less, 
until  at  rupture  it  is  perhaps  less  than  half  the  original  area,  as  shown 
in  Fig.  10. 

11.  The  Significant  Results  of  a  Tensile  Test. — There  are  five  signifi- 
cant results  of  a  tensile  test,  namely: 

The  Modulus  of  Elasticity; 

The  Elastic  Limit; 

The  Ultimate  Strength; 

The  Percentage  of  Elongation; 

The  Reduction  of  Area  of  Cross-section. 

The  Modulus  of  Elasticity  is  found  by  dividing  any  stress  per  square 
inch  below  the  elastic  limit  by  the  corresponding  proportionate  deforma- 
tion. Since  the  stress-diagram  is  a  straight  line  from  the  origin  to  the 
elastic-limit  point,  any  point  on  this  portion  of  the  locus  may  be  selected 
for  the  determination  of  the  modulus  of  elasticity.  For  instance,  if  the 
point  which  represents  an  elongation  of  0.1  of  one  per  cent  be  chosen,  the 
deformation  being  0.001  (see  Fig.  6),  the  modulus  of  elasticity  is  found 
at  once  by  multiplying  the  corresponding  stress  in  pounds  per  square  inch 
by  1000.*  In  other  words,  the  modulus  of  elasticity  is  the  tangent  of  the 
angle  which  that  portion  of  the  stress-diagram  below  the  elastic  limit  forms 
with  the  horizontal  axis  when  the  two  coordinates  are  properly  evaluated 
by  the  vertical  and  horizontal  scales  respectively. 

It  is  a  very  remarkable  fact  that  the  modulus  of  elasticity  of  all  grades 
of  wrought  iron  and  rolled  steel,  from  the  softest  up  to  the  highest  grade  of 
spring  steel,  is  nearly  constant,  and  has  a  value  from  29,000,000  to 
30,000,000,  being  perhaps  always  within  the  limits  of  27,000,000  and 
31,000,000  pounds  per  square  inch.  The  ultimate  strength  of  these  metals 
varies  from  about  45,000  to  several  hundred  thousand  pounds  per  square 
inch  for  the  strongest  steel  wire;  but  through  this  range  of  variation  of 
strength  the  ratio  of  the  stress  to  the  corresponding  deformation  re- 
mains nearly  constant.  The  modulus  of  elasticity  is,  therefore,  a  very 
valuable  quality  of  such  materials  and  one  which  is  made  great  use  of  in 

*  If  the  diagram  is  not  straight  to  this  point  (has  its  elastic  limit  below  this  point), 
then  draw  a  tangent  to  the  diagram  at  the  origin,  aud  note  where  it  ciits  the  ordinate 
marking  a  deformation  of  0.001,  aud  this  stress  multiplied  by  1000  is  the  modulus  of 
elasticity.  This  modulus  can  be  read  off  in  this  manner  from  any  of  the  stress  dia- 
grams for  tension  and  compression  found  in  this  work. 


18  THE  MATERIALS  OF  CONSTRUCTION. 

engineering  design.  It  may  be  called  the  modulus  of  stiffness,  since  it  is  a 
direct  measure  of  the  rigidity  of  a  body,  or  an  inverse  measure  of  its  flexi- 
bility.* 

12.  The  True  Elastic  Limit  is,  in  general,  from  50  to  70  per  cent  of  the  ulti- 
mate strength  of  the  material,  while  the  apparent  elastic  limit  is  from  GO  to 
70  per  cent  of  the  ultimate  strength  of  the  material.     The  apparent  elastic 
limit,  or  the  breaking-down  point,  is  also  the  ultimate  strength  for  practical 
purposes,  since  almost  all  materials  lose  their  value  in  structural  designs 
after  they  have  been  deformed  beyond  this  limit. 

The  true  elastic  limit  may  be  defined  either  as  the  deformation  where 
permanent  set  begins,  or  as  a  point  beyond  which  a  given  increment  of  load 
produces  a  greater  increment  of  deformation,  which  is  the  point  where  the 
ratio  of  the  stress  to  the  deformation  ceases  to  be  a  constant  and  begins  to 
diminish.  This  is  also  the  upper  extremity  of  the  straight  portion  of  the 
stress-diagram.  If  a  material  like  wrought  iron  or  structural  steel  be  loaded 
beyond  its  true  elastic  limit,  and  even  beyond  its  yield-point,  and  the  load 
removed,  the  material  has  been  permanently  elongated;  but  if  it  again 
be  subjected  to  a  load,  it  will  be  found  to  be  perfectly  elastic  up  to  the  limit 
of  its  previous  loading.  In  other  words,  its  elastic  limit  has  been  raised  to 
the  value  of  its  previous  loading.  In  this  way  the  elastic  limit  can  be  raised 
practically  up  to  the  ultimate  strength.  When  the  term  "  elastic  limit  "  is 
used  in  a  scientific  sense  without  modification,  the  true  or  primitive  elastic 
limit  (point  A,  Fig.  4)  is  always  to  be  understood;  but  when  used  in  a  com- 
mercial sense,  the  apparent  elastic  limit  or  yield-point  (point  B)  is  to  be 
taken. 

As  stated  previously,  the  elastic  limit  is  usually  found  in  commercial 
testing  by  noting  the  action  of  the  weighing-beam  in  dropping  under  an 
increasing  stretch,  this  being  in  fact  the  breaking-down  point.  To  determine 
the  true  elastic  limit  it  is  necessary  to  use  very  delicate  measuring  appli- 
ances, which  will  enable  the  observer  to  discover  when  the  ratio  of  stress 
to  deformation  has  begun  to  change.  Even  when  using  such  devices  the 
readings  must  be  plotted  to  a  large  scale  to  detect  the  deviation  from  a 
straight  line. 

13.  "  The  Apparent  Elastic  Limit"  is  defined  by  the  French  Commission 
as  "  the  load  per  square  millimeter  of  the  original  section,  where  the  defor- 
mation begins  to  increase  sensibly  with  no  increase  in  the  external  force 
applied  (corresponding  to  the  dropping  of  the  beam  in  testing-machines)."! 
Since  in  most  kinds  of  materials  there  is  no  such  point  other  than  the  ulti- 

*  A  modulus  of  flexibility  would  be  the  reciprocal  of  the  modulus  of  elasticity,  or  — . 

IL 

but  Prof.  A.  B.  W.  Kennedy  has  taken  for  such  a  modulus  of  "specific  extension"  the 
stretch  in  thousandths  of  an  inch  on  a  length  of  10  inches  under  a  stress  of  1000  Ibs.  per 
sq.  in.     Its  reciprocal  multiplied  by  10,000,000  is  the  modulus  of  elasticity, 
f  Report  of  the  French  Commission,  vol.  i.  p.  207. 


MATERIALS    UNDER  TENSILE  STRESS. 


19 


mate  strength,  and  since  in  these  materials  an  elastic  limit  corresponding  to 
sensible  deformations  is  required  for  practical  purposes,  the  author  proposes 
to  extend  the  meaning  of  this  term  so  as  to  make  it  applicable  to  all  elastic 
materials,  and  at  the  same  time  to  make  it  serve  as  the  "  elastic  limit "  to 
be  universally  used  in  all  kinds  of  practical  tests.  For  this  purpose  he 
employs  the  following  definition : 

The  apparent  elastic  limit  is  the  2wint  on  the  stress-diagram  of  any 
material,  in  any  kind  of  test,  at  which  the  rate  of  deformation  is  fifty  per 
cent  greater  than  it  is  at  the  origin* 

This  point  is  found  either  by  comparing  increments  of  deformation  with 
given  increments  of  load,  or  better  by  plotting  the  stress-diagram  and  draw- 
ing a  tangent  to  it  which  has  an  inclination  to  the  vertical  50  per  cent  greater 
than  has  the  tangent  to  the  diagram  at  the  origin,  as  shown  in  Fig.  9.  To 


/V 


0.. 


l/M. 


T  / 


'M 


O  N 
&'5 


ft 


A/-C 


\ 


0 
FIG.  9.— Stress- diagram  of  Hard-drawn  Steel  Wire.     (  Wat.  Ars.  Hep.,  1890.) 

do  this  lay  off  the  tangent  to  the  curve  at  the  origin  (or  inside  the  true 
elastic  limit,  where  it  is  a  straight  line),  and  then  fix  a  point  on  any  hori- 
zontal line  of  the  paper,  50  per  cent  farther  from  the  vertical  axis  than  the 
point  where  this  tangent  cuts  it.  Lay  a  parallel  ruler  on  this  point  and  the 
origin,  and  move  it  till  it  becomes  tangent  to  the  curve  and  draw  the  tan- 

*  This  definition  should  not  be  made  to  apply,  however,  to  materials  not  perfectly 
elastic  within  any  limits.  Thus  certain  stones  and  concretes  have  stress-diagrams  which 
are  reversed  curves,  their  rates  of  deformation  being  greater  at  first  than  after  they  are 
heavily  loaded,  and  any  load  produces  a  permanent  set,  as  shown  in  Chapter  XXXI. 
Here  the  modulus  of  elasticity  is  different  for  every  increment  of  load,  and  no  kind  of 
"elastic  limit"  can  be  attributed  to  them.  That  is  to  say,  they  are  not  perfectly 
elastic  for  any  load  however  small. 


20  THE  MATERIALS  OF  CONSTRUCTION. 

gent  line.    Then  fix  the  point  of  tangency  by  the  eye,  and  call  this  the 
apparent  elastic  limit.*' 

This  fixes  a  point  which  in  all  cases  corresponds  to  an  extremely  small 
permanent  deformation.  In  Fig.  9  the  permanent  deformation  at  this 
limit,  for  hard-drawn  steel  wire,  is  about  0.0003  of  the  length,  or  Tfg-  of  one 
per  cent,  while  the  limit  so  fixed  is  some  22,000  Ibs.  per  sq.  in.  above  the 
true  elastic  limit.  Although  this  test  was  made  at  the  U.  S.  Arsenal  at 
AVatertown,  Mass.,  and  on  the  Emery  testing-machine,  with  extreme  accu- 
racy, as  shown  by  the  accordance  of  the  results  when  plotted  to  the  large 
scale  in  Fig.  9,  yet  the  "  elastic  limit "  as  set  down  in  the  published  record 
(which  "  elastic  limit "  is  supposed  to  be  the  "  true  elastic  limit  ")  lies  some 
8000  Ibs.  per  sq.  in.  higher  than  the  "  apparent  elastic  limit "  fixed  by  the  rule 
here  laid  down!  This  same  state  of  affairs  is  shown  in  numberless  cases  in 
the  recorded  results  of  tests  made  at  this  the  most  fruitful  and  accurate  labo- 
ratory in  the  world. f  While,  therefore,  objection  would  be  quickly  raised 
to  the  criterion  herein  proposed  for  fixing  an  "  apparent  elastic  limit-"  in  so 
arbitrary  a  manner,  and  apparently  so  far  beyond  the  "  true  elastic  limit,"  yet 
no  one  would  be  inclined  to  question  the  records  of  the  U.  S.  Watertown 
Arsenal  tests,  in  the  fixing  of  a  "true  elastic  limit,"  even  though  this  should 
in  nearly  all  cases  lie  beyond  this  conventional  "apparent  limit  "!  After  a 
great  deal  of  thought  and  research  given  to  this  subject,  the  author  believes 
no  better  criterion  can  be  found  for  fixing  a  practical  "  elastic  limit"  which 
will  be  one  and  the  same  limit  for  a  given  material  in  the  hands  of  all  ex- 
perimenters, and  on  all  machines.  For  all  materials  which  have  a  definite 
"  yield-point  "  this  "  apparent  elastic  limit,"  determined  as  here  described, 
will  agree  with  it  exactly;  but  for  such  materials  it  would  never  be  deter- 
mined in  this  manner,  since  it  is  then  so  much  more  readily  found  by  the 
"  drop  of  the  beam,"  or  even  by  a  pair  of  dividers  set  to  given  marks  on  the 
specimen.  For  all  materials  which  have  no  point  of  "yielding  under  a 
fixed  load"  at  this  stage  of  the  test,  this  criterion  would  always  accomplish 
the  following  results : 

1.  It  would  always  fix  one  and  the  same  well-defined  point. 

2.  This  point  would  always  correspond  to  so  small  a  permanent  defor- 
mation as  to  be,  for  all  practical  purposes,  the  true  elastic  limit. 

3.  It  is  equally  applicable  to  all  materials  which  have  an  elastic  field. 

4.  It  is  equally  applicable  to  all  kinds  of  tests,  whether  on  specimens  or 
on  finished  members  or  structures,  where  deformations  of  any  kind  can  be 
correctly  measured. 

While  the  50  per  cent  increase  in  the  rate  of  deformation  is  purely  arbi- 

*The  author  has  done  this  in  his  U.  S.  timber  tests  since  1891,  calling  this  point  in 
his  cross-bending  stress-diagrams  "the  relative  elastic  limit." 

f  See  other  instances  in  records  selected  therefrom  for  this  work  in  Chapters  XXV 
and  XXVI. 


MATERIALS   UNDER  TENSILE  STRESS.  21 

trary,  it  is  not  large  enough  to  fix  a  point  having  an  appreciable  permanent 
set,  but  it  is  large  enough  to  fix  a  well  defined  point  on  the  stress-diagram. 
A  very  extended  experience  in  its  application,  therefore,  serves  but  to  con- 
firm the  author  in  its  continued  use,  and  in  the  recommendation  of  its  gen- 
eral adoption  which  is  here  put  forth  for  the  first  time.  * 

14.  The  Ultimate  Strength  of  a  specimen  subjected  to  tensile  stress  is. 
measured  by  the  maximum  load   carried,  and   is  indicated  on  the  stress- 
diagram  by  the  true  maximum  point  in  that  curve.     It  is  found  by  dividing^ 
the  maximum  breaking  load  by  the  original  area  of  cross-section.     In  case 
of  the  more  plastic  metals,  the  area  of  the  broken  section  is  usually  about 
one  half  the  original  area,  so  that  the  ultimate  strength  of  the  actual  section 
at  rupture  when  found  by  dividing  the  breaking  load  by  the  final  area  of 
this  section  would  be  about  twice  the  ultimate  strength  as  computed  on  the 
original  section.     That  is  to  say,  the  drawing  down  and  pulling  out  of  the 
metal  has  nearly  doubled  its  strength  per  square  inch.     The  term  "  ultimate 
strength"  however,  ahvays  refers  to  the  original  section,  and  is  found  bij 
dividing  the  maximum  load  by  the  original  section. 

15.  The  Percentage  of  Elongation  is  found  by  dividing  the  increase  of 
length  after  rupture  has  occurred,  by  the  original  length.     By  original 
length  is  meant  a  certain  portion  of  the  specimen  which  has  been  reduced 
to  a  uniform  cross-section  before  testing.     A  standard  length  for  tensile-' 
test   specimens   in   America    and    in    England    is   eight   inches,   while   in 
Germany  and  France  it  is  twenty  centimeters,  these  standard  lengths  being 
practically  identical.     The  elongation  of  a  test   specimen  of  the  plastic 
metals  may  be  divided  into  two  portions:  (a)  that  part  of  the  elongation 
which   is   uniformly   distributed    over   the   section;    (I))  that   part   of   the 
elongation  which  occurs  in  the  vicinity  of  the  section  which  finally  breaks. 
Thus  in  Fig.  10  are  shown  four  sets  of  test  specimens  of  mild  steel,  there 
being  three  specimens  in  each  set.     All   the  specimens  of  one  set  were 
originally  of  the  length  indicated  by  the  untested  specimen  which  stands 
on  the  left  side  of  each  group.     The  specimen  next  adjoining  it  on  the 
right  has  been  stretched  to  the  limit  of  the  elongation  indicated  in  (a) 
above,  or  until  there  is  an  indication  of  a  local  reduction  of  area.     The 
right-hand  specimen  in  each  group  shows  the  local  elongation  and  reduc- 
tion, but  the  specimen  has  been  removed  from  the  testing-machine  before 
rupture  occurred.     The  middle  specimen  of  each  group  has  been  tested  to- 
the  ultimate  strength  of  the  material,  since,  when  the  specimen  begins  to- 
reduce  locally,  the  ultimate  strength  has  been  passed,  and  the  strain-diagram 
begins  to  fall,  or  it  is  developed  under  a  diminishing  load. 

By  the  amount,  therefore,  that  the  right-hand  specimen  in  each  of  these 
groups  is  longer  than  the  middle  specimen  of  the  group,  by  so  much  has 
the  length  been  increased  by  the  local  drawing  out  on  the  section  where 
failure  will  finally  occur.  The  first  elongation,  therefore,  is  that  portion 
which  is  uniformly  distributed  over  the  specimen,  and  the  second  is  that 

*  See  also  Arts.  261,  262,  and  263,  pages  306-311. 


THE  MATERIALS   OF  CONSTRUCTION. 


MATERIALS   UNDER  TENSILE  STRESS.  23 

which  is  concentrated  in  the  vicinity  of  the  final  failure.  Both  of  these 
elongations  are,  however,  measured  and  included  in  the  total  elongation, 
from  which  the  percentage  of  elongation  is  determined.  The  total  elonga- 
tion is  obtained  after  rupture  has  occurred,  by  placing  the  two  ends  together 
and  measuring  the  distance  between  the  primitive  gauge-marks.  In  the 
case  of  specimens  having  shoulders  at  their  ends  the  gauge-marks  should 
be  at  least  one-half  inch  inside  of  the  shoulder,  since  the  metal  adjacent  to 
the  shoulder  does  not  elongate  fully,  because  of  the  strengthening  effect 
of  the  enlarged  cross-sections  at  the  ends. 

It  will  at  once  be  apparent  from  a  study  of  these  specimens  that  the 
(1}  elongation,  or  that  which  is  locally  developed  in  the  vicinity  of  final 
rupture,  is  nearly  the  same  in  all  these  specimens;  whereas  the  (a)  elonga- 
tion, or  that  which  is  uniformly  distributed  over  the  specimen,  is  always 
directly  proportional  to  the  length.  The  total  elongation,  therefore,  will 
not  be  proportional  to  the  length.  In  other  words,  the  percentage  of  total 
elongation  will  be  greater  for  the  short  specimen  than  for  the  long  ones. 
This  shows  the  necessity  of  using  standard  lengths  of  these  specimens  when 
the  percentage  of  elongation  is  to  be  found. 

The  percentage  of  elongation  is  the  result  which  indicates  the  ductility 
of  the  material,  this  being  one  of  the  most  important  qualities  of  the 
metals  used  in  structural  designing. 

16.  The  Reduction  of  Area  of  Cross-section  is  found  by  determining  the 
area  of  the  broken  cross-section,  subtracting  this  from  the  original  area  of 
cross-section,  and  dividing  the  difference  by  the  original  area.  This  is  not, 
so  important  an  indication  or  result  as  the  others  described  above,  but  it  is 
customary  to  determine  it,  and  to  add  it  to  the  record.  For  the  ductile 
metals  this  reduction  of  area  may  be  as  much  as  from  fifty  to  sixty  per  cent, 
of  the  original  cross-section. 


CHAPTER   III. 
MATERIALS   UNDER  COMPRESSIVE   STRESS. 

17.  Two  Classes  of  Engineering  Materials. — Engineering  materials  may 
be  divided  into  two  general  classes,  according  to  their  manner  of  failure  in 
compression. 

Plastic  or  viscous  materials  are  those  which  will  flow  without  showing 
any  other  indication  of  failure  under  a  sufficient  compressive  load. 

Brittle  or  comminuible  materials  are  those  which  will  crush  to  a  pow- 
der, or  crumble  to  pieces,  or  fail  by  shearing  on  definite  angles  under  a 
compressive  load. 

In  the  former  class  are  such  materials  as  wrought  iron,  soft  and  medium 
steel,  the  alloys,  lead,  copper,  zinc,  and  the  like.  Of  the  latter  class  are  cast 
iron,  hard  or  tempered  steel,  brick,  stone,  cement,  etc.  The  laws  of  failure 
of  these  two  classes  are  very  different,  and  they  will,  therefore,  have  to  be 
discussed  separately. 

18.  Crushing  Strength  of  Plastic   or  Viscous  Materials. — There  is   no 
such  thing   as  an  "ultimate  strength  "in  compression   of  a  plastic  body. 
There  is,  however,  a  definite  "apparent  elastic  limit,"  the  same  as  in  ten- 
sion.    Beyond  this  limit  the  material  simply  spreads,  and  increases  the  area 
of  its  cross-section  indefinitely  under  an  increasing  load,  as  shown  in  Plate 
II.     The  elastic  limit  in  compression  of  such  a  material  is  the  greatest  load 
from  which  the  specimen  will  fully  recover,  or  it  is  the  greatest  load  within 
which  the  stress  and  deformation  bear  a  constant  ratio  to  each  other.     This 
elastic  limit    in  compression  for  wrought    iron   and    steel  is,   fortunately, 
about  the  same  in  pounds  per  square  inch  as  the  elastic  limit  in  tension. 
It  is  not  customary,  therefore,  to  test  such  materials  in  compression,  but 
to  assume  that  they  have  the  same  elastic  limit  in  compression  which  they 
are  found  to  have  in  tension. 

19.  The  Law  Governing  the  Strength  in  Compression  of  a  Brittle  or  Com- 
minuible Material. — Experiments  show  that  all  such  materials  when  sub- 
jected to  a  compressive  load  fail  by   shearing   on  certain  definite  angles. 
The  resistance  to  movement  along  these  angles  is  made  up  of  two  parts: 
first,  the   strength    of   the    material    to   resist   shearing;    and    second,  the 
frictional  resistance  to   motion  along  this  plane.     The  sum  of  these  two 
resistances  must  equal  the  shearing  component  of  the  load  imposed  when 

24 


PLATE   II. 


Wrought  Iron. 


Steel. 


Wrought  Iron. 


Steel. 


Steel. 


Wrought  Iron. 


Wrought  Iron.  Steel. 

RELATIVE  MALLEABILITY  OP  WROUGHT  IRON  AND  SOFT  STEEL. 
All  the  specimens  were  originally  of  the  shape  of  the  one  remaining  umleformed. 
The  wrought  iron  specimens  uniformly  show  large  cracks.     (From  von  Tetmajcr's  Com- 
munications, vol.  iv,  PI.  V.N 


MATERIALS    UNDER   COMPRESSIVE  STRESS. 


resolved  along  the  shearing  plane.  To  find  what  this  angle  should  be,  we 
may  equate  the  two  resistances  here  described  with  the  shear- 
ing force,  and  find  the  angle  of  rupture,  the  determining 
condition  being  that  this  angle  shall  be  that  which  offers  the 
least  total  resistance  to  failure  under  a  crushing  load.  This 
angle  may  be  found  in  the  following  manner: 

Let  s  =  shearing  strength  of  the  material  per  square  inch; 
A  =  area  of  prism  =  1  square  inch; 
6  =  angle  of  rupture; 
p  =  crushing  load  per  square  inch. 

The  tendency  to  slide  on  the  plane  of  rupture  is  p  sin  0. 

The  resistance  to  sliding  is  s  sec  0  -\-  fp  cos  0,  where /is 
the  coefficient  of  friction  =  tan  0,  where  0  =  angle  of  re- 
pose. Hence,  at  failure, 

p  sin  0  =  s  sec  0  -\-fp  cos  0.       .     .     . 


FIG.  11. 


(1) 


It  is  evident  that  the  angle  of  rupture  will  be  such  as  to  cause  failure 
under  the  least  load;  hence  if  0  be  taken  as  the  independent  variable,  we 
shall  have  at  rupture 


j-  =  -  s(cos2  0  -  sin2  0  -f  2f  sin  0  cos  0)  =  0, 


,,-r 


cos'"  0  —  sin2  0 
•'  ~         2  sin  0  cos  0 


cos 


sin  20 


=  -  cot  20.      ,     .     .     (2) 


Whence,  since/  =  tan  0,  we  have 

tan  0  =  -  cot  20  =  —  tan  (90°  -  20)  =  tan  (20  -  90°), 


or 


=  20-90°      and      0  =  -       ^—-  =  45°  +  ^.      .     .     .     (3) 


That  is  to  say,  the  angle  of  rupture  is  45°  plus  one  lialf  the  angle  of  repose. 
If  the  friction  had  been  omitted,  we  should  have  had 

p  sin  0  =  s  sec  0;     whence     -L  =  —  s(cosa  0  —  sin2  0)  =  0; 

l-2sin20  =  0;     2  sin1  0  =  1,     or     0  =  45°.      .     .     .     (4) 

It  has  been  customary  to  neglect  the  friction,  and  to  state  that  the 
plants  of  rupture  make  this  angle  of  45°  with  the  horizontal;*  but  the 
actual  plane  of  rupture,  when  the  specimen  has  sufficient  height,  is  about 

*  Coulomb  is  responsible  for  this  -theory,  while  Navier  has  given  the  true  analysis. 
Most  writers,  including  Rankine,  have  followed  Coulomb,  however. 


26  THE  MATERIALS  OF  CONSTRUCTION. 

55°  with  the  horizontal,  or  35°  from  the  direction  of  the  applied  load.  See 
Figs.  12  and  13,  showing  tests  on  sandstone  made  by  Prof.  Bauschinger.) 
Mr.  Charles  Bouton  has  shown*  that  the  theoretical  angle  of  rupture  is 


FIG.  12. — Bausehinger's  Compression  Tests  oil  Sandstone. 

borne  out  in  practice  with  many  kinds  of  materials.  (See  Fig.  14  for 
photographic  views  of  crushed  specimens  of  cast-iron  cylinders  of  various- 
heights,  showing  angle  of  rupture.) 

The  following  table  gives  the  results  of  Mr.  Bouton's  determinations  of 
the  theoretical  and  the  actual  values  of  this  angle: 

*  In  u  thesis  for  the  degree  M.S.  at  Washington  University,  1891,  entitled  Theory 
and  Experiments  on  the  Laws  of  Crushing  Strength  of  Short  Prisms.  Mr.  Bouton  also  de- 
rived the  formulae  in  this  article  and  afterwards  found  that  Navier  had  anticipated  him. 


MATERIALS   UNDER  COMPRESSIVE  STRESS. 


27 


Observed 

Observed 

Theoretical 

Number 

Angle 

Angle 

Angle 

Material. 

of 
Experi- 

of Rupture. 

of  Repose. 

of  Rupture. 

th 

Differences. 

ments. 

0 

* 

45-  +  | 

41  F  "  cast  irou  

24 

54°.  8  ±  0°.2 

20°.  6 

55°.  3 

-  0°.5 

"  C.  W."  cast  iron  

24 

55  .0  ±  0  .2 

16   .9 

53  .4 

+  1    .6 

Limestone          

4 

62.2 

33   .4 

61  .7 

-f  0  .5 

Asphiilt  paving  mixture 
"Milwaukee  brick 

3 

4 

59.7 

58.2 

27  .3 
27  .0 

58  .6 
58  .5 

+  1   .1 
—  0.3 

FIG.  13.— Bauschinger's  Compression  Tests  on  Sandstone. 


28  THE  MATERIALS  OF  CONSTRUCTION. 

The  u  F."  cast  iron  was  good  foundry  iron,  having  a  tensile  strength  of 
22,000  pounds  per  square  inch  and  a  modulus  of  elasticity  of  14,500,000; 
the  "  C.  W."  iron  was  car-wheel  iron,  having  a  tensile  strength  of  20,000 


FIG.  14.—  Bouton's  Compression  Tests  on  Cast  Iron. 

pounds  per  square  inch  and  a  modulus  of  elasticity  of  6,500,000,  or  less 
than  one  half  of  the  former. 

20.  Relation  of  Crushing  Strength  to  Shearing  Strength.—  To  show  the 
relation  of  the  crushing  strength  to  the  shearing  strength,  we  have,  from 
equation  (1)  in  the  previous  article, 


s  =  ;?(sin  6  cos  6 
also,  from  equation  (2), 


'  0); 


~  cos  2^  cos2  0  —  sin7  9 

j    — —    __  nQr  v  £7  — — —    __ 

sin  26  2  sin  6  cos  6 


Substituting  this  value  of/,  we  find 
_  p  cos  0  _ 


(5) 


MATERIALS   UNDER  COMPRESSIVE  STRESS.  29 

or 

p  =  2s  tan  0,     ..........          /g\ 

where  p  =  compressive  strength  in  pounds  per  square  inch,  arid 
s  =  shearing  strength  in  pounds  per  square  inch. 

This  relation  was  also  shown  by  Mr.  Bouton  to  be  well  borne  out  in 
practice.  The  great  trouble  to  prove  such  a  relation  is  to  find  s  experi- 
mentally on  brittle  materials  without  introducing  bending  stresses  (See 
Art.  37.) 

21.  Relation  of  Crushing  Strength  to  Relative  Dimensions  of  Specimen.  _ 
This  is  a  very  important  matter.  Hitherto  nearly  all  crushing-test  speci- 
mens of  brittle  materials  have  had  a  cubical  form.  So  long  as  the  theoreti- 
cal angle  of  rupture  was  thought  to  be  45°  this  was  proper;  but  since  this 
theoretical  angle  approaches  60°,  it  is  evident  that  the  height  of  the  speci- 
men should  be  at  least  one  and  one  half  times  the  least  lateral  dimension, 
in  order  to  allow  of  failure  on  a  normal  angle.  Prof.  Bauschinger  has 
studied  this  question  very  exhaustively,  and  the  following  conclusions  are 
drawn  from  studies  of  his  results  of  tests  on  a  very  uniform  quality  of  fine 
Swiss  sandstone,  all  possible  refinements  as  to  appliances  having  been 
introduced  :  * 

He  recommends  the  formula 


for  all  shapes  of  cross-section  and  for  all  relative  heights,  where 
p  =  crushing  strength  per  unit  of  area; 
A  =  area  of  cross-section ; 
u  =  perimeter  of  cross-section; 
h  =  height  of  specimen; 
a  and  &  =  constants. 
For  rectangular  cross-sections  the  following  formula  serves  very  well : 

4/~j 
p  =*+**£, .     (8) 

where  k  and  k'  are  constants. 

The  application  of  this  formula  is  shown  in  Fig.  15,  in  which  the  tests  were 
on  three  sets  of  sandstone  prisms  of  the  dimensions  2-j-  in.  by  5  in.,  3f  in. 
by  5  in.,  and  5  in.  by  5  in.  in  cross-section,  respectively,  the  heights  of  each 
set  varying  from  one-half  to  five  times  the  least  lateral  dimension.  It  is 

* Mittheilungen  aw  dem  Mechanisch  TechniscJien  Laboratorium  der  K.  TecJinischen 
Hoclischule  in  MuncJien,  von  J.  Bauschinger,  vol.  vi,  1876. 


30 


THE  MATERIALS   OF  CONSTRUCTION. 


V 


X 


4000 


1 


1 


wr 


<?       AS      w 

FIG.  15. — Relation  between  Crushing  Strength  per  square  inch  and  Ratio  of  Cross 
section  to  Height  of  Specimen.     (Bauschiuger.) 


£000 


FIG.  16. — Relation  between  the  Crushing   Strength  per  square  inch  and  the  Ratio 
Height  to  Least  Lateral  Dimension.     (Bauschinger  and  Bouton.) 


MATERIALS   UNDER   COMPREBSIVE  STRESS.  31 

rident  that  formula  (8)  fits  the  results  very  well,  the  equation  of  the  full 
lie  being 

p  =  5600  -f  1400-y— (9) 

li 

\  pounds  per  square  inch. 
If  a  simpler  formula  is  desired,  the  following  may  be  chosen: 


(10) 


here  ~bl  =  least  lateral  dimension. 

Fig.  16  shows  how  well  this  law  fits  the  observations,  the  equation  for 
lis  locus  being,  for  the  tests  on  sandstone, 

5500  +  1565^  .........     (11) 

The  lower  curve  in  Fig.  16  represents  the  law  for  sandstone  prisms,  and 
le  upper  one  the  law  for  cast-iron  cylinders,  when  the  strength  argument 
Q  the  diagram  is  multiplied  by  ten.  The  experiments  for  the  former  were 
lade  by  Prof.  Bauschinger,  for  the  latter  by  Mr.  Bouton.  Mr.  Bouton 
lade  his  tests  on  two  kinds  of  cast  iron,  using  five  bars  of  each  and 
.irning  from  these  ten  bars  nearly  one  hundred  cylinders.  The  tests  on 
:ie  longer  cylinders  have  been  excluded  from  the  results  plotted,  as  their 
mgth  caused  them  to  bend  greatly,  and  hence  their  failure  did  not  follow 
le  law  for  short  prisms.  The  plotted  points  on  the  tests  of  cast  iron 
3present  the  average  results  of  the  number  of  similarly  proportioned 
ylinders.  In  these  tests  there  seems  to  be  a  possible  minimum  point  at 

bout  -  =  1.5,  this  being  about  the  height  which  equals  tan  0,  or  the  least 
ct 

eight  offering  an  opportunity  for  failure  on  the  theoretical  angle.  Why 
lis  should  be  the  case  does  not  appear,  and  the  mean  curve  has  been  drawn 
ithout  showing  such  a  minimum  indication. 

22.  Relative  Strength  of  Prisms  ~  and  Cubes.—  In  order  to  show  the 
3lation  of  the  strength  of  a  prism  to  that  of  a  cube  Bauschinger's  observa- 

ons  were  used,  as  plotted  in  Fig.  16  to^>  and  •=-,  and  the  curve  as  shown 

i  Fig.  17  is  the  result.* 
Thus,  from  this  mean  curve,  we  have  the  equation 

strength  of  prism 


Q 
strength  of  cube  h  ' 

rhere  bl  =  least  lateral  dimension,  and  li  =  height  of  prism. 
This  equation  shows  that  the  strength  of  a  stone  prism  whose  height  is 

*  This  law  holds  between  the  limits  h  =  0.4&  and  h  =  56,  these  being  the  limits  of 
ie  observations. 


32 


THE  MATERIALS  OF  CONSTRUCTION. 


one  and  one  half  times  its  least  lateral  dimension  has  a  strength  equal 
92$  of  the  strength  of  a  cube  of  the  same  material. 

This  height  of  =-  =  -  was  found  to  be  necessary  to  allow  the  materi 
i 

to  shear  on  the  theoretical  angle  of  45°  -j-  ~.     Hence  when  the  cubic 


form  is  used  for  test  specimens  in  crushing,  the  results  are 
if  the  proper  height  of  specimen  had  been  chosen. 


greater  th; 


ay 

0.4  d<3  /.2  {6  £0  2.4  2.8  3.2  d£  40  44  48  S.2 
FIG.  17.  — Relation  between  the  Crushing  Strength  of  Prisms  and  Cubes. 

Also,  if  a  brick,  for  instance,  be   tested   flatwise,  in  which   positi 
-1  =  2,  we  find  from  this  curve  it  will  give  a  result  22$  greater  than  tl 

for  a  cube,  and  33$  greater  than  that  for  a  specimen  in  which  r'  =  - 

ft  O 

other  words,  the  results  from  tests  on  cubes  are  9$  too  large,  and  on  brie 
flatwise  they  are  33$  too  large. 

It  will  also  be  noted  that,  so  far  as  these  tests  go,  the  unit  strength 
the  material  is  no  function  of  the  size  of  the  specimen,  but  only  afunch 
of  its  form. 

23.  Effects  of  Loading  a  Portion  of  the  Cross-section.* — (a)  Chamfei 
Edges. — If  the  edges  of  a  cube  or  prism  be  chamfered  off  as  shown 
Fig.  18,  and  the  load  applied  uniformly  over  the  reduced  area,  the  law 


*  All  the  tests  discussed  in  this  article  are  taken  from  Prof.  Bauschmger's  publisl 
reports,  but  the'author  of  this  work  has  discussed  them  witn  the  results  as  given. 


MATERIALS   UNDER  COMPRESSIVE  STRESS. 


the  variation   of   strength   with  varying   areas   of   compressed   surface   is 
shown  by  the  curves  on  this  figure. 

Thus,  as  the  area  of  pressed  surface  approaches  that  of  the  full  cross- 
section,  the  load  carried  per  unit  of  pressed  surface  decreases,  as  shown  by 
the  curved  locus  at  the  top,  while  the  average  load  on  the  full  cross-section 


^000 


/q000 


n 


000 


0000 


J000 


2000 


FIG.  18.— Crushing  Streugth  of  Cubes  with  Chamfered  Edges.     (Bausclringer.) 

increases  uniformly,  as  shown  by  the  straight  locus  of  Fig.  18,  the  two  loci 
meeting  at  9500  pounds,  the  strength  per  square  inch  of  a  full  cube. 

These  results  show  clearly  that  the  bearing  surface  should  be  that  of 
the  full  cross-section  of  the  specimen  if  normal  results  are  to  be  obtained. 
The  contrary  has  sometimes  been  asserted — that  the  strength  of  the 
specimen  was  not  increased  appreciably  by  the  material  outside  the  bearing 
surface.  In  other  words,  crushing -test  specimens  should  be  true  prisms  in 
form,  without  chamfered  edges  or  rounded  corners. 

Since  the  locus  of  unit  strength  for  bearing  surface,  Fig.  18,  comes 
nearly  into  a  horizontal  direction  as  the  pressed  surface  approaches  the  full 
area  of  cross-section,  it  follows  that  when  the  pressed  surface  is  nearly 
equal  to  that  of  the  full  cross-section  of  the  specimen  the  error  introduced 


34 


THE  MATERIALS  OF  CONSTRUCTION. 


by  considering  only  the  pressed  surface  is  very  small.  For  instance,  if  the 
area  of  the  compressed  surface  is  0.8  that  of  the  full  cross-section  (dimen- 
sions of  cross-section  0.9  those  of  the  full  section),  the  error  introduced  by 
considering  the  pressed  surface  only  would  be  by  this  curve  -^VW  —  3.2^. 

(b)  Square  Bearing,  Symmetrically  Placed. — AVhen  the  pressed  surface 
is  square  and  placed  symmetrically  on  a  larger  cube,  the  relation  of  the 
resistance  per  unit  of  pressed  surface  to  the  strength  of  the  cube  is  shown 
on  Fig.  19.  Here  the  curves  are  given  for  the  small  bearing  on  one  side 


I, 


w 

$    < 


S000 
6000 
S000 
#000 


FIG.  19. — Effect  of  Loading  a  Portion  only  of  the  Surface  of  a  Cube.     (Bauscliinger.) 

and  also  on  opposite  sides,  and  the  crushing  resistance  computed  and 
plotted  per  unit  of  bearing  surface  and  also  per  unit  of  cross-section  of  the 
cube.  Evidently  the  loci  must  all  meet  at  a  point  where  the  bearing  area 
equals  the  total  area  on  each  side,  and  this  point  will  be  the  strength  of  a 
cube  of  this  material,  which  was  9500  pounds  per  square  inch,  the  same  as 
shown  in  Fig.  18,  the  material  being  the  same. 


MATERIALS   UNDER  COMPRESSIVE  STRESS. 


35 


(c)  Bearing  Surface  Rectangular  and  Extending  Entirely  Across  the 
Cube. — In  this  case  the  resistance  per  square  inch  is  a  function  of  the  dis- 
tance of  the  pressed  surface  from  the  edge  of  the  cube.  This  law  is  shown 
in  Fig.  20.  The  material  being  the  same  as  before,  the  strength  of  a  cube 


26000 


22000 


/sooo 


/OOOO 


&OOO 


2000 


s 


Iff  LL'L/l- 


//zz 


/0  20  30  40  JO  ffl  7O  £0  00  W 

FIG.  20.— Effect  of  Loading  a  Zone  on  the  Surface  of  a  Cube.     (Bauschinger.) 

would  be  9500  pounds  per  square  inch.  This  corresponds  to  a  distance 
from  the  edge  of  the  cube  equal  to  8$  of  the  half-width.  As  the  bearing- 
surface  had  a  width  equal  to  10$  of  the  half-width  of  the  specimen,  it  fol- 
lows that  the  outer  line  of  the  pressed  surface  came  within  3$  of  the  half- 
width,  or  \\%  of  the  total  width  from  the  edge  of  the  specimen  when  the 
normal  strength  of  the  material  was  developed.* 

24.  General  Laws  of  Crushing  Strength. — The  laws  of  crushing  strength 
shown  in  Figs.  15  to  20  apply  specifically  to  a  particular  quality  of  sand- 
stone. In  Fig.  16  it  is  shown  that  cast  iron  follows  a  different  law.  In  all 
probability  each  kind  of  material,  or  at  least  materials  which  have  different 
angles  of  rupture  (that  is  to  say,  different  coefficients  of  friction),  will  show 
different  curves  for  the  several  relations  indicated  in  these  plates.  In  the 
absence  of  any  more  definite  information,  however,  on  this  subject,  it  is 
thought  the  curves  shown  upon  these  plates  will  serve  to  indicate  in  a 
general  way  the  laws  of  the  variation  of  crushing  strength  with  the  varying 
conditions  here  indicated. 


*  See  figures  12  and  13  for  methods  of  failure  for  cases  (a),  (5),  and  (c). 


36 


THE  MATERIALS  OF  CONSTRUCTION. 


By  referring  to  Fig.  14  [it  will  be  observed  that  the  cylinders  all 
swelled  more  or  less  in  the  middle  before  rupture  occurred.  This  is  doubt- 
less due  to  the  restraining  action  of  the  friction  against  lateral  motion  on 
the  end  bearing  surfaces.  It  is  difficult  to  take  this  source  of  strength 
fully  into  account  in  a  theoretical  analysis  of  resistance  to  crushing. 

25.  Strength  of  Columns. — When  a  compression  member  is  so  long  as 
to  fail  in  compression  by  lateral  deflection,  its  failure  is  a  function  of  the 
•elastic-limit  strength  and  of  the  stiffness   (modulus  of  elasticity)  of  the 
material,  rather  than  of  the  ultimate  strength  of  the  material  in  compres- 
sion.    The  discussion  of  this  case  properly  comes  in  works  on  mechanics 
and  on  framed  structures.     The  author  has  fully  expressed  his  views  on  this 
question  in  his  work  on  Modern  Framed  Structures,  and  to  some  extent  in 
Chapter  XVI  of  this  work,  and  hence  he  will  not  occupy  space  with  it  here. 

26.  Weakening  Effects  of  Eccentric  Loading. — Few  persons  are  aware 
of  the  great  increase  of  stress  on  the  near  side  of  a  member  subjected  to  a 

n  n  n  ~~~      direct  stress  (either  tension  or  compres- 

sion) caused  by  an  eccentricity  of  the 
load-line  with  reference  to  the  gravity- 
axis  of  the  member.  This  eccentricity 
may  result  from  an  eccentric  imposi- 
tion of  the  load  itself;  or  from  the 
member  being  bent;  or  from  the  ad- 
dition of  material  on  one  side  of  the 
member,  such  addition  usually  prov- 
ing a  source  of  weakness  instead  of 
strength.  These  three  cases  are  shown 
in  Fig.  21.  In  each  case  we  have 

Total  load      =  P; 
"     area      =  A ; 

Eccentricity  =  a\ 

Width  =h; 

Moment  of  inertia  of  section  =  /; 

Radius  of  gyration  of  section  =  r; 

Distance  of  extreme  fibre  from  the 

gravity-axis  =  yl  =  —  with  symmetrical 
A 


T 


•a 


FIG.  21. 


sections; 
Total  stress  on  nearest  outer  fibre  =/. 


h 


Hence  we  have  for  symmetrical  cross-sections,  where  y,  =  — , 

A 


*  The  stress  due  to  the  bending  moment  Pa  is  found  from  the  equation  m  =  —   or 

#i 

/=        ,  where  m  =  Pa,  and  /  =  Ar*. 


MATERIALS   UNDER  COMPRESSIVE  STRESS.  37 

For  solid  rectangular  cross-sections  we  have    r2  =  —  =  —  ;   hence  for 

A.        LA 

such  sections 


The  proportionate  increase  in  the  stress,  therefore,  over  that  which 
would  obtain  for  a  concentric  load  is  given  by  the  fraction  y  .  In  other 

words,  when  a  =  ^h  the  stress  on  the  outer  fibre  on  the  near  side  is  doubled, 
compared  with  that  for  a  central  loading. 

To  discover  the  weakening  effect  of  additional  material  added  to  one 
side  of  a  member,  assume  a  central  loading  on  a  straight  symmetrical 
member  having  an  initial  width  =  h,  (a  =  o).  If  additional  material,  to  a 
thickness  of  x,  be  now  added  on  one  side  of  this  member,  the  new  total  width 

x 
becomes  h  -\-  x,  and  the  eccentricity  is  a  =  —  .     Assuming  the  member  to  be 

solid  rectangular  in  cross-section,  with  original  dimensions  of  b  and  h,  the 
new  dimensions  of  section  are  b  and  h-\-x;  the  former  area  was  A  =  bh,  and 

P      P 

the  latter  A'  =  b(h  -{-  x).     Before  the  addition  we  should  have/=  —  =  —  . 

A       Oil 

After   the  addition   we   should   have,   from    (14),   for   the   stress    on   the 
near  side, 

0.) 

Hence  the  increase  of  the  stress  due  to  an  unsymmetrical  addition  of 
material  is 

(16) 

This  is  zero  for  x  =  0  and  for  x  =  2h,  and  it  is  a  maximum  for  x  =  -, 
when  it  becomes 


Hence  we  may  say  that  the  addition  of  material  on  one  side  of  a  mem- 
ber subjected  to  a  direct  stress  symmetrically  placed  weakens  it  until  the 
added  material  has  exceeded  twice  the  original  thickness  of  the  member,  the 
maximum  weakening  occurring  when  the  added  material  is  one  half  the 
original  thickness,  when  the  enlarged  member  is  only  three  fourths  as 
strong  as  the  original  member.* 

*  Attention  was  called  to  this  fact  by  Mr.  Carl  G.  Earth  in  Trans.  Engrs.  Club  of 
Phila.,  Oct.  1891,  p.  307. 


CHAPTER  IV. 
MATERIALS  UNDER  SHEARING  STRESS. 

27.  Two  Manifestations  of  Shearing  Stress. — When  all  the  opposing 
external  forces  which  act  on  a  body  lie  in  one  plane,*  but  not  in  one  and 
the 'same  line,  the  resisting  stresses  are  those  of  simple  shear  and  cross- 
bending,  without  torsional  stress. 

When  the  opposing  external  forces  do  not  lie  in  one  plane  the  resisting 
stresses  are  those  of  torsional  shear,  with  or  without  cross-bending  and 
simple  shear. 

In  any  case  these  three  kinds  of  stress  are  determined  separately,  as 
follows : 

(a)  For   Parallel  External   Forces   in    One   Plane. — The   moment  oi 
resistance  of  the  bending  (direct)  stresses  at  any  transverse  section  is  equal 
to  the  algebraic  sum  of  the  moments  of  tho  external  forces  on  either  side  oi 
that  section  taken  about  the  neutral  axis  in  that  section. 

The  simple  shearing  stress  on  any  section  is  equal  to  the  algebraic  sum 
of  the  transverse  components  of  the  external  forces  on  either  side  of  that 
section. 

(b)  For  Parallel  External  Forces  Not  in  One  Plane. — First  replace  all 
the  forces  by  equal  parallel  forces  acting  in  the  plane  of  the  axis  of  the  body; 
and  by  couples  equal  in  value  in  each  case   to   the   force  multiplied   by 
its  displacement.     Then  the  moments  of  resistance  and  the  simple  shearing 
stresses  will  be  the  same  as  in  the  last  case,  and  in  addition  there  will  be* 
the  moment  of  torsion. 

The  torsional  moment  at  any  transverse  section  is  equal  to  the  algebraic 
sum  of  the  moments  of  the  couples  of  the  displaced  forces,  acting  on  either 
side  of  the  transverse  section  in  question, 

(c)  For  Non-parallel  Forces  Acting  in  Any  Manner. — Resolve  all  forces 
into  horizontal  and  vertical  components  at  their  points  of  application,  and 
then  solve  for  bending  moments,  shears,  and  torsions  at  any  section  in  these 
two  planes.  ;' 

The  bending  moment  at  this  section  will  then  be  the  square  root  of  the 
sum  of  the  squares  of  the  bending  moments  at  right  angles  to  each  other. 

*  When  a  force  is  distributed  over  an  area  it  is  here  supposed  to  act  at  the  centre- 
of  gravity  of  these  force-elements. 


MATERIALS    UNDER  SHEARING   STRESS. 


39 


The  total  shear  will  also  be  the  square  root  of  the  sum  of  the  squares  of 
the  primary  shears  at  right  angles  to  each  other. 

The  total  moment  of  torsion  will  be  the  algebraic  sum  of  the  two 
moments  of  torsion  found  from  the  two  sets  of  forces. 

28.  The  Moment  of  Torsion  gives  rise  to  a  shearing  stress  over  the  entire 
cross-section,  which  is  zero  at  the  centre  of  gravity  of  the  section,  and 
which  increases  in  intensity  directly  as  the  radial  distance  from  the  gravity 
axis. 

For  various  forms  of  sections,  the  following  intensities  of  shearing  stress 
are  found,  by  the  principles  of  mechanics,  for  the  corresponding  forms  of 
cross-section. 

The  general  equation  for  resistance  to  torsion  is 


.a) 


Figure. 


Dimensions. 


i  Radius  =  r. 


Outer  radius  =  r    (. 
Inner       "       =  t\  ( 


Side  =  b. 


3uter  dimension  =  b 
[uner  "          =  b1 


Side  =  a. 


Radius    of   circumscribed 
circle  =  r 


Longer  axis  =  2a  I 
Shorter  axis  =  26 ) 


longer  semi-axes=a&ct1  » 
Shorter    "        "     =6&6X  ) 


Area. 


&a 


62  -  6^ 


3a2      _ 


2,-a  |/2 


irab 


rr(ab—  a161) 


J* 


nr*_ 

~2~ 


+  2^2) 


4    - 


2r 


31/2 


3  1/2 


1.083o» 


1.876r» 


~(os  +  &a) 


40  THE  MATERIALS  OF  CONSTRUCTION. 

•where  M  —  total  torsional  moment; 

s  =  shearing  stress  on  extreme  fibre; 

J*  =  polar  moment  of  inertia  of  cross-section  about  the  gravity  axis 

r  —  distance  from  neutral  axis   to   the  extreme   fibre   having   th 

shearing  stress  s. 

Whence  we  have,  for  the  forms  figured,  the  relations  given  in  th 
table. 

29.  Shearing  Deformations.— As  shown  in  Arts.  (7)  and  (8),  a  shearin 
action  of  external  forces  results  in  angular  deformation  of  the  body.  L 
the  case  of  simple  shear,  or  where  the  forces  lie  in  one  plane,  the  angula 
deformation  from  shear  is  very  small,  the  bending  being  mostly  due  to  th 
longitudinal  deformations  resulting  in  the  direct  tensile  and  compressiv 

resisting  stresses  on  the  two  sides  of  th 
neutral  plane  respectively.  When  th 
forces  do  not  lie  in  one  plane,  or  wher 
there  is  a  moment  of  torsion,  the  angula 
deformation  gives  rise  to  a  twist  of  th 
body  about  the  neutral  longitudinal  axis 
Thus  in  Fig.  23  assume  the  solid  cylindei 
anchored  at  o,  to  have  a  length  /  and 

radius  r.     Let   the   torsional   moment  be  Pa  =  Mt.     Then  the   shearin. 
stress  on  the  extreme  fibre  is,  by  equation  (1), 

_  Mtr  _  2Pa 

where  J"is  the  polar  moment  of  inertia  =  twice  the  rectangular  moment  o 
inertia  in  this  case. 

In  Art.  9  the  shearing  modulus  of  elasticity  was  defined  as 

„   __  shearing  stress  per  sq.  in. 
angular  deformation 

If  we  take  the  stress  and  angular  deformation  of  the  outer  fibre  i 
Fig.  23,  we  have : 

2  Pa 
Shearing  stress  per  sq.  in.  =  s  —  — -r. 

Tangent  of  the  deformation  angle  —  -=•  =  deformation  angle, 

since  this  angle  is  small. 
Hence  we  have 


„  _  _  si 

8  ~        ~ 


*  The  student's  attention  is  called  to  the  fact  that  the  polar  moment  of  inertia 
equal  to  the  sum  of  the  true  rectangular  moments  of  inertia  about  the  principal  ax 
through  the  centre  of  gravity  of  the  section. 


MATERIALS    UNDER  SHEARING  STRESS.  41 

or 


In  general,  for  any  cross-section  we  have 

„       Mtl       si  Mtl        si 

s  =    ~  == 


where  y^  —  distance  from  the  neutral  axis  to  the  extreme  fibre  in  which  the 
stress  is  s. 

In  Art.  9  it  was  shown  that  the  shearing  modulus  of  elasticity  —  f  of 
Young's  modulus,  or  Es  =  \E.  Hence  in  terms  of  Young's  modulus  of 
elasticity,  which  is  that  ordinarily  given,  we  have 

5    MJ,^5sl_ 
2  '  EJ      ZEyS 

where  6  =  angular  movement  in  terms  of  the  radius; 
Mt  =  torsional  moment  on  the  bar; 
I  —  length  of  bar  between  sections  representing  a  relative  angular 

movement  of  0; 

s  =  shearing  stress  on  outer  fibre; 
Es  —  shearing  modulus  of  elasticity  of  the  material; 
E  =  the  ordinary  modulus  of  elasticity; 

J  =  polar  moment  of  inertia  =  Ix  -\-  Iy,  where  these  are  the  rectan- 
gular moments  of  inertia  about  the  principal  axis  through  the 
centre  of  gravity  of  the  section  ; 

y^  =  distance  from  neutral  axis  of  outer  fibre  in  which  the  shearing 
stress  is  s. 


CHAPTER   V. 
MATERIALS  UNDER  CROSS-BENDING  STRESS. 

30.  Historical  Sketch.*— For  two  hundred  and  fifty  years  the  true  theory  of  the 
strength  of  a  beam  has  been  a  much-mooted  question  amongst  physicists,  engineers, 
and  mathematicians. 

Galileo  was  the  first  of  whom  we  have  any  record  who  undertook  to  discuss  the 
problem.  In  his  famous  Dialogues  (Leiden,  1638,  from  which  Fig.  24  is  taken)  he 


FIG.  24. 

propounds  a  theory  based  on  an  assumed  absolute  rigidity  of  the  material,  and  con- 
cluded that  the  fibres  of  the  beam  were  subjected  to  a  uniform  tension  which  acted  I 
about  the  base  of  the  beam  as  a  fulcrum.  On  this  theory  the  moment  of  resistance 

*  This  historical  review  of  the  development  of  the  true  theory  of  the  beam  is  derived! 
mostly  from  Saint-Venant's  Historique   Abrege  des  Recherches  sur  la  Resistance  et  sur- 
I ' Elasticite   des  Corps  Bolides,  prefixed  to  his  Navier's  "Lecons,"  Third  Edition,  Paris,, 
1864,  and   from  Totlhunter's  History  of  the  Theory  of  Elasticity,    Cambridge,   Eng., 
1886.     It  is  here  reprinted  from  the  author's  joint  work  on  Modern  Framed  Structures. 

42 


MATERIALS   UNDER  CROSS-BENDING  STRESS.  43 

of  a  solid  rectangular  beam  would  be  — — ,  where  /  is  the  ultimate  strength  of  the 

material  in  tension. 

Robert  Hooke  first  published  his  famous  law  of  the  relation  between  deformation 
and  stress  in  1678,  discovered  by  him  he  says  18  years  previously,  and  kept  secret  for 
the  purpose  of  procuring  patents  on  some  applications  of  the  principle  to  springs' for 
watches,  clocks,  etc.  Two  years  previously  he  had  ventured  to  publish  the  law  in 
an  anagram  at  the  end  of  another  book,  in  this  form,  "  ciiiinosssttuv"  which 
being  interpreted  reads,  "Ut  tensio  sic  vis,"  or, '4as  the  extension  so  is  the  resist- 
ance." Hooke  makes  this  law  apply  to  all  "springy"  bodies,  amongst  which  he 
names  nearly  all  ordinary  solids.  This  is  still  known  as  Hooke  s  Law. 

Mariotte  showed  by  experiment  in  1680  that  the  fibres  on  one  side  of  the  beam 
were  extended  and  on  the  other  side  compressed,  and  assumed  that  the  neutral 
surface  passes  through  the  centre  of  gravity  of  the  section. 

Varignon,  in  1702,  undertakes  to  harmonize  the  theories  of  Galileo  and  Mari- 
otte, by  admitting  the  extension  of  the  fibres,  but  puts  the  neutral  plane  at  the  bot- 
tom, as  Galileo  did,  and  assumes  the  tensile  stress  as  uniformly  varying  from  there 

to  the  other  side.     This  would  make  the  strength  of  a  solid  rectangular  beam  - — -, 

3 

which  agrees  almost  exactly  writh  the  facts  for  cast  iron  at  rupture  when  f  is  the 
tensile  strength. 

James  Bernouilli  made  an  important  advance  by  applying  Mariotte's  law  to 
obtain  deflections  of  beams  (1694  and  1705),  and  argued  that  the  position  of  the 
neutral  axis  is  a  matter  of  indifference,  which  was  a  great  error.  He  denied  the 
truth  of  Hooke's  law,  which  we  know  is  not  applicable  to  all  substances,  nor  to  the 
point  of  rupture  with  any  substance.  He  first  constructed  stress  diagrams,  but 
his  work  in  the  field  of  hydraulics  was  of  even  greater  importance  than  in  the  study 
of  solids. 

A.  Parent,  a  French  academician,  seems  to  have  been  the  first  to  perceive  (1713) 
the  mechanical  necessity  of  equilibrium  between  the  tensile  and  compressive  stresses, 
which  condition,  together  with  that  of  a  uniform  variation  of  stress,  fixes  the  posi- 
tion of  the  neutral  axis  at  the  centre  of  gravity  of  the  section.  This  important  dis- 
covery seems,  however,  to  have  passed  unnoticed. 

Coulomb  reannounced  this  relation  in  a  memoir  to  the  French  Academy  in  1773, 
or  sixty  years  after  its  first  publication  by  Parent.  Saint- Venant  credits  Coulomb 
with  never  having  seen  Parent's  work,  as  no  writer  of  that  century, has  mentioned 
it.  But  even  after  this  second  publication  of  so  important  a  necessary  truth,  such 
workers  as  Girard,  Barlow,  and  Tredgold  all  misconceived  the  mathematical  necessi- 
ties in  the  problem,  and  resorted  to  various  makeshifts  to  explain  the  strength  of 
beams.  - 

Navier  finally,  in  1824,  put  the  matter  on  a  solid  mathematical  basis,  although 
he  also  at  first  went  entirely  astray.  He  stated  in  his  first  edition  that  the  moment 
of  resistance  varied  as  the  cube  of  the  depth  of  the  beam,  and  in  his  second  edition 
this  error  was  corrected,  but  the  moment  of  the  stresses  on  one  side  of  the  neutral 
axis  was  said  to  be  equal  to  the  moment  of  the  stresses  on  the  other  side,  about  that 
axis,  an  equality  which  does  not  exist  except  on  symmetrical  sections.  Navier  also 
fully  developed  the  theory  of  the  deflection  of  beams  as  we  now  use  it. 

Saint-Venant,  a  student  of  Navier's,  has  finally  (1857)  in  his  notes  on  Navier's 
Lemons  given  a  complete  analysis  of  both  the  elastic  and  the  ultimate  strength  of  a 
beam,  with  suitable  equations  which  will  give  theoretical  results  agreeing  with  the 
actual  tests,  when  the  empirical  constants  are  properly  evaluated.  This  great  engi- 
neer, physicist,  and  teacher  has  done  more  than  any  other  one  to  bring  theory  and 
practice  into  harmony  and  to  put  both  on  a  thoroughly  scientific  basis,  so  far  as  the 
strength  and  elasticity  of  engineering  materials  is  concerned.* 

In  spite  of  these  various  true  expositions  of  this  subject  the  source  of 
strength  in  a  beam  continues  still  to  be  very  imperfectly  understood  by 

*  He  died  January  6,  1886. 


THE  MATERIALS  OF  CONSTRUCTION. 


many  engineers,  and  even  by  current  writers  on  applied  mechanics,  and 
gross  errors  in  this  direction  are  still  common.  It  is  in  consideration  of 
this  state  of  the  science  that  the  problem  is  treated  so  fully  here. 

31.  Fundamental  Equations  of  Equilibrium. — When  a  solid  body  is  in 
equilibrium  under  the  action  of  non-concurrent  external  forces,  the  follow- 
ing propositions  hold  true  for  the  body  as  a  whole: 

I.  The  sum  of  the  vertical  components  of  /he  external  forces  is  equal 
to  zero. 

II.  The  sum  of  the  horizontal  components  of  the  external  forces  taken  in 
any  plane  is  equal  to  zero. 

III.  The  sum  of  the  moments  of  the  external  forces  taken  about  any 
point  is  equal  to  zero. 

When  a  solid  body  is  subjected  to  the  action  of  non-concurrent  forces 
acting  in  one  plane  the  body  may  be  regarded  as  a  beam,  since  the  effect  of 
the  external  forces  is  to  bend  the  body  and  develop  in  it  what  are  commonly 

called  cross-bending  stresses.  If  a  section 
be  passed  through  the  body  perpendicular 
to  the  plane  of  the  forces,  and  the  portion 
of  the  body  on  one  side  of  this  section  be 
removed, the  other  portion  may  beheld  in 
equilibrium  with  the  external  forces  act- 
ing upon  it,  by  means  of  the  stresses  exist- 
ing in  the  body  on  this  cross-section,  these 
stresses  now  being  regarded  as  external 
forces,  as  indicated  in  Fig.  25.  Since  the 
remaining  portion  of  the  body  now  under 
consideration  is  in  equilibrium  under  the 
action  of  external  forces  and  of  internal 
stresses,  which  for  the  time  may  be  re- 
garded as  external  forces,  the  three  propositions  given  above  will  apply. 
Or,  stating  these  propositions  now  so  as  to  equate  the  real  external  forces 
with  the  internal  stresses  developed  at  the  section,  they  would  read  as 
follows : 

If  a  transverse  section  be  passed  through  a  beam— 

I.  The  sum  of  the  vertical  components  of  the  stresses  acting  at  the  sec- 
tion is  equal  to  the  sum  of  the  vertical  components  of  the  external  forces 
acting  upon  the  body  on  either  side  of  that  section. 

II.  The  sum  of  the  horizontal  components  of  the  stresses  acting  on  the 
section  is  equal  to  the  sum  of  the  horizontal  components  of  the  external 
forces  acting  upon  the  body  on  either  side  of  that  section. 

III.  The  sum  of  the  moments  of  the  stresses  acting  on  that  section  i? 
equal  to  the  sum  of  the  moments  of  the  external  forces  acting  on  the  body  on 
either  side  of  that  section. 

It  follows  from  the  above  that  if  all  the  external  forces  acting  upon 


FIG.  25. 


MATERIALS    UNDER   CROSS- B ENDING  STRESS.  45 

a  beam  are  parallel  vertical  forces,  the  end  reactions  or  supports  being 
regarded  as  external  forces  the  same  as  any  primary  weights  or  loads,  and 
if  no  horizontal  forces  act  upon  the  beam,  then  we  should  have  for  any  ver- 
tical section — 

I.  The  shearing  stress  is  equal  to  the  algebraic  sum  of  the  external  forces 
acting  on  either  side  of  the  section. 

II.  The  algebraic  sum  of  the  horizontal  stresses  acting  on  the  section  is 
equal  to  zero. 

III.  The  algebraic  sum  of  the  moments  of  the  stresses  acting  on  that 
section,  which  is  commonly  Called  the  moment  of  resistance,  is  equal  to  the 
sum  of  the  moments  of  the  external  forces  about  any  point  in  that  section. 

The  effect  of  the  action  of  cross-bending  forces  upon  a  beam  is  to  bend 
or  deflect  it,  thus  shortening  the  lengths  of  the  fibres  or  elements  on  the 
concave  side  of  the  beam,  and  lengthening  them  on  the  convex  side.  So 
long  as  this  action  does  not  exceed  the  elastic  limits  of  the  material,  the  re- 
sisting stresses  are  directly  proportional  to  the  deformations.  Hence  there 
is  always  found  a  compress! ve  stress  on  the  concave  side  and  a  tensile  stress 
on  the  convex  side  of  a  beam,  and  therefore  there  will  be  a  plane  near  the 
centre  of  the  beam  the  elements  of  which  are  neither  lengthened  nor 
shortened,  and  on  which  there  will  be  no  longitudinal  stress.  This  is 
called  the  neutral  plane  or  "  neutral  axis"  of  the  beam. 

Furthermore,  a  geometrical  effect  of  the  bending  of  a  beam  is  to  pro- 
dace  deformations  which  are  zero  at  the  neutral  plane  and  which  increase 
uniformly  outward  to  the  extreme  convex  and  concave  sides,  and  hence  the 
longitudinal  resisting  stresses  developed  by  these  deformations  also  increase 
uniformly  outward.  AVithin  the  elastic  limits,  therefore,  the  direct  stresses 
increase  uniformly  from  the  neutral  plane  to  the  extreme  fibre*. 

Since  from  Proposition  II,  as  stated  above,  the  summation  of  the  hori- 
zontal stresses  on  the  cross-section  is  zero,  in  simple  cross-bending,  where 
the  external  forces  have  no  horizontal  components,  it  follows  that  the  total 
summation  of  the  tensile  stresses  on  the  convex  side  of  the  neutral  plane  must 
always  exactly  equal  the  total  summation  of  the  compressive  stresses  on  the 
concave  side.  Also  by  Proposition  III  the  sum  of  the  moments  of  all  these 
stresses  taken  about  any  point  in  this  plane  must  equal  the  sum  of  the 
moments  of  the  external  forces  acting  on  either  side  of  the  section  taken 
about  the  same  point.  If  this  centre  of  moments  be  taken  in  the  neutral 
plane  itself  it  will  at  once  be  evident  that  the  moment  of  the  tensile  forces 
on  one  side  has  the  same  sign  as  the  moment  of  the  compressive  forces  on 
the  other  side,  and  that  they  are,  therefore,  to  be  added  together  numer- 
ically in  order  to  equal  the  algebraic  sum  of  the  moments  of  the  external 
forces  acting  on  either  side  of  the  section.  While,  therefore,  the  sum  of  the 
moments  of  the  tensile  stresses  may  be  numerically  equal  to  the  sum  of  the 
moments  of  the  compressive  stresses  (which  is  the  case  for  symmetrical 
cross-sections),  yet  since  they  are  to  be  added  together  numerically,  in  order 


46 


THE  MATERIALS  OF  CONSTRUCTION. 


to  equal  or  hold  in  equilibrium  the  moments  of  the  external  forces  on  one 
side  of  the  section,  there  is  evidently  no  mathematical  necessity  why  the 
moments  of  the  compressive  stresses  should  equal  the  moments  of  the  tensile 
stresses;  and  in  unsymmetrical  sections,  and  even  in  symmetrical  sections 
beyond  the  elastic  limit,  these  moments  are  not  equal  to  each  other. 

Since  the  stresses  on  any  cross-section  of  a  beam  subjected  to  the  action 
of  bending  forces  increase  uniformly  from  the  neutral  plane  to  the  extreme 
sides,  it  is  evident  that  it  is  only  the  stress  found  to  exist  in  the  extreme 
fibres  or  elements  of  the  beam,  which  needs  to  be  determined.  That  is  to 
say,  if  the  maximum  stresses  are  kept  within  the  working  limits,  it  is  imma- 
terial what  the  particular  stresses  are  on  other  portions  of  the  cross-section. 
It  is  common,  therefore,  to  find  the  relation  between  the  total  moment  of 
resistance  of  a  beam  (which  of  necessity  is  always  numerically  equal  to  the 
bending  moment  of  the  external  forces),  and  the  stresses  on  the  extreme 
fibres  or  elements  of  the  cross-section  of  the  beam.  This  general  relation 
between  the  bending  moment  and  the  stresses  on  the  extreme  fibres  is  made 
the  subject  of  the  following  article. 

32.  Relation  between  the  Moment  of  Resistance  and  the  Stress  on  the 
Extreme  Fibre. — In  Fig.  26  let  the  load  P  be  applied  at  (7,  and  this  will 


! 

LH  , 

(S)     \y 

c        /K  i  - 

j 

k 

; 

\ 

p 

FIG.  26. 

produce  a  bending  moment  on  AB  of  Pd.     On  this  plane  the  moment  of 
the  longitudinal  stresses  makes  up  the  moment  of  resistance  which  holds  in 
equilibrium  (and  hence  is  always  numerically  equal  to)  the  bending  moment 
of  the  external  forces.     That  is  to  say,  M=  Pd  =  M0 ,  the  moment  of  resist- 
ance.    We  shall  here  assume  the  cross-section  to  be  irregular  and  unsym- 
metrical,  as  shown  in  the  figure.     The  direct  stress  varies  uniformly  across 
the  section  in  all  cases.     The  following  notation  will  be  used  : 
M  =  bending  moment  of  the  external  forces. 
M0  =  moment  of  resistance  of  the  direct  stresses  =  M. 
p  =  intensity  of  the  direct  stress  at  the  distance  ?/  from  the  neutral 
plane  —  ay,  where  a  =  intensity  of   direct  stress  at  a  unit's 
distance. 

f  =  intensity  of  the  direct  stress  at  the  extreme  side  of  the  beam. 
y1  =  distance  of  extreme  fibre  on  one  side  from  the  neutral  axis. 
v  '  =         "        "        "          "      "  the  other  side  from  the  neutral  axis. 


MATERIALS   UNDER   CROSS-BENDING  STRESS.  47 

/ =  y*dxdy  —  moment  of  inertia  of  the  cross-section  about  the  centre 

of  gravity  axis, 
y  =  distance  from  axis  of  reference  to  the  centre  of  gravity  of  the 

cross-section. 
Intensity  of  stress  on  any  fibre  =  p  =  ay\ (1) 

Total  stress  on  fibre  having  an  area  of  dxdy  =  pdxdy  =  ay  dxdy ',    .     .     (2) 
Moment  of  stress  on  fibre  dxdy  = pydxdy  =  ay*  dxdy; (3) 

/+»! 
y*dxdy  —  al.  .     (4) 
2/1' 

But  SLS  p  =  ay,  so/=  ayt  and/'  =  ayf\  or 


Therfeore 

fl*       f'l 
M  -  Mn  =  al  =  -  -  =  J—r (5) 

I  y*     y' 

This  is  the  general  equation  between  the  moment  of  resistance  and  the 
stress  on  either  extreme  fibre.  When  the  section  is  symmetrical,  y  ^  =  yf\ 
hence  f  =  f'9  and  only  one  side  need  be  considered. 

When  the  cross-section  is  solid  and  rectangular,  equation  (5)  becomes 


(6) 


The  above  demonstration  assumed  that  the  neutral  axis  or  plane  of  the 
beam  passed  through  the  centre  of  gravity  of  the  cross-section,  since  /was 
referred  to  this  gravity  axis.  This  remains  to  be  proved. 

From  equation  (2)  we  have,  the  stress  on  any  element  is  ay  dxdy,  where 
y  is  measured  from  the  neutral  axis.  But  for  simple  cross-bending  the 
algebraic  sum  of  these  direct  stresses  over  the  whole  section  is  zero;  hence 
we  have 


But 


/+Vl  /»+»!  /»+01 

aydxdy  —  a  I  ydxdy  —  a  I  ydA  =  0  .....     (?) 
-VT!  "-Hi!  */-Vi' 

fydA=yA,\      .............     (8) 

*Both  equation  (5),  M0  =—  ,  for  any  section,  and  equation  (6),  MQ  —  \fbli*  t  for  solid 

y\ 

rectangular  section,  should  be  thoroughly  memorized  by  the  student,  as  they  are  of  con- 
stant application. 

f  The  symbol  y  denotes  the  distance  from  the  axis  of  y  to  the  centre  of  gravity  of  the 

f  ydxdy      f  ydxdy 

cross-section,  and  it  equals  —  —  . 

Jdxdy  A 


48 


THE  MATERIALS   OF  CONSTRUCTION. 


since  the  sum  of  the  statical  moments  of  the  elementary  areas  about  any 
axis  is  equal  to  the  moment  of  the  total  area  into  the  distance  to  its  centre 
of  gravity.  Therefore  we  have,  for  reference  to  the  neutral  axis, 


/H-2/1 

i  I  yd  A  =  0, 
*'—«.' 


or     yA  —  0. 


(9) 


But  yA  can  only  equal  zero  when  reference  is  made  to  the  gravity  axis- 
Therefore  these  two  axes  must  coincide.  In  other  words,  the  neutral  plane 
always  traverses  the  centre  of  gravity  axis  of  the  beam,  so  long  as  the 
stresses  remain  inside  the  elastic  Hunts  of  the  material  in  both  tension 
and  compression,  and  also  provided  the  modulus  of  elasticity  is  the  same 
for  both  kinds  of  stress. 

33.  Moments  of  Resistance  (Strength)  of  Beams  of  Various  Forms  of 
Cross-section. — The  moment  of  resistance  of  a  beam  of  any  form  of  cross- 


Form  of 
Cross-  section. 

Distance  of  Centre 
of  Gravity, 
or  Neutral  Axis, 
from  the 
Most  Distant  Fibre. 

Moment  of  Inertia 
about  the 
Centre  of  Gravity 
of  the 
Section. 

=  7 

Moment  of  Resistance 
in 
Terms  of  the  Stress 
in  the 
Most  Distant  Fibre. 

--£ 

*6  > 

h 
If 

6/1,3 

12 

>• 

•O: 

d 
~2 

vd* 
64 

£/d> 

¥ 

le" 

1 

24^  ;' 

i*  "  o  "*• 

T7V 

h 

12 

7 

V> 

6  ^//IJ 

">'^?T" 

1 

bh*  -  (b  -  t'yh  -  2f)3 

57^3  _  ^  -  t'yh  -  2t)3f 

'"2Ei. 

12 

6/1 

/IE 

lt'h*  +  t(b  -t')(h-  JO 

b/j,3  _  (b  -  t'yh  -  t)3 

fl 

t'h  +  <(6  -  V) 

3 

Vi 

^*   . 

6  +  26'     fc 

^rBft-f*'      (6+26')^ 

//^r3(36  +  6')(6  +  60 

/^       \  * 

6  +  6'  *  3 

k  L    12          18(6  +  6')  J 

eL       2(6  +  26')           (6+26U 

$' 

MATERIALS    UNDER   CROSS-BENDING  STRESS.  49 

section  was  found  to  be,  by  equation  (5),  Ma  =• — ,  where  /=  intensity  of 

stress  on  the  extreme  fibre  which  lies  at  a  distance  from  the  neutral  plane 
equal  to  ylt  and  /is  the  rectangular  moment  of  inertia  of  the  cross-section 
about  the  neutral  or  gravity  axis.  In  the  table  on  p.  48  are  given  the 
values  of  ?/,,  /,  and  M0  for  various  forms  of  sections  which  are  commonly 
used  as  beams.  For  tabular  and  graphical  methods  of  finding  the  moments 
of  inertia  of  irregular  forms,  see  Modern  Framed  Structures,  pages  127-130. 

The  values  given  in  the  above  table  are  true  for  all  values  of /inside  the 
elastic  limit.  When  this  limit  is  exceeded  the  stress  no  longer  varies  uni- 
formly across  the  section,  but  the  stresses  near  the  neutral  axis  are  larger 
than  the  above  theory  allows,  and  hence,  for  a  given  actual  stress  on  the 
extreme  fibres  beyond  the  elastic  limit  (as  the  breaking-stress,  for  instance), 
the  moment  of  resistance  is  much  more  than  would-be  obtained  by  using 
the  breaking  value  of /(in  tension  Of  compression)  and  substituting  this  in 
the  above  formulae.  It  must  be  understood,  therefore,  that  in  no  case  are 
these  formulae,  true  at  rupture,  but  only  inside  the  elastic  limits  of  the  ma-. 
terial.  It  is  for  this  reason  that  the  values  of /as  found  from  cross-bending 
tests  carried  to  failure,  and  as  computed  from  the  above  formula?,  differ  so 
largely  from  the  breaking  values  of  the  material  in  direct  tension  or  com- 
pression.* Thus,  cast  iron,  which  has  a  tensile  strength  of  20,000  pounds 
per  square  inch  and  which  breaks  on  the  tension  side  in  cross-breaking,  has 
a  value  of/,  when  computed  by  the  above  formulae  from  a  breaking-load,  of 
from  30,000  to  40,000  pounds  per  square  inch,  depending  somewhat  on  the 
shape  of  the  cross-section  of  the  specimen.  The  more  the  material  is  con- 
centrated near  the  neutral  plane  the  more  the  value  of /differs  from  the 
tensile  strength.  This  value  of/  computed  from  the  breaking  moment,  is 
called  the  modulus  of  rupture  in  cross-breaking.  It  is  from  1.5  to  2  times 
the  tensile  strength  of  the  metal. 

In  timber  beams  the  reverse  is  the  case;  that  is  to  say,  the  crushing 
resistance  being  less  than  the  tensile  resistance,  the  modulus  of  rupture  in 
cross-breaking  is  greater  than  the  former  and  less  than  the  latter,  and  it  is 
in  fact  nearly  a  mean  of  the  two. 

34.  Strength  (Moment  of  Resistance)  of  Beams  beyond  their  Elastic  Limits. 
— After  the  stress  on  the  extreme  fibres  on  one  or  both  sides  of  the  beam 
has  passed  the  elastic  limit,  the  distribution  of  stress  over  the  section  is  no 
longer  uniformly  varying  as  was  assumed  in  deriving  the  formulae  of  the 
last  article,  and  the  law  of  this  variation  will  now  be  examined. 

In  all  cases  the  variation  of  stress  across  the  transverse  section  of  a, 
beam  subjected  to  simple  cross-bending,  with  or  without  shearing  stress, 
folloivs  the  law  of  the  variation  of  the  stress  ordinates  to  a  stress-diagram 


*  See  a  full  discussion  of  this  subject  iii  the  author's  work  on  Modern  Framed 
Structures,  Chapter  VIII. 


50 


THE  MATERIALS  OF  CONSTRUCTION. 


in  which  the  extreme  ordinate  represents  the  stress  on  the  extreme  fibre  of 
the  beam. 

Thus  in  Fig.  28,  suppose  the  beam  to  be  cast  iron,  and  to  be  bent  until 
the  stress  on  the  extreme  fibre  on  the  tension  side  has  become  ft.     Passing 


FIG.  28. 

now  to  the  tension  portion  of  the  stress-diagram  for  this  material,*  we  see- 
that  this  stress,/,,  is  found  far  beyond  the  elastic  limit  of  the  metal  in  ten- 
sion. Let  us  now  recur  to  the  fact  that  the  deformation  of  the  longitudinal 
fibres  of  the  beam  increases  uniformly  outward  from  the  neutral  axis,  even 
beyond  the  elastic  limit,  since  the  section  remains  sensibly  plane,  and  hence 
the  uniform  increase  of  the  deformation  is  a  geometrical  necessity.  In 
view  of  this  fact  it  becomes  evident  that  the  law  of  increase  of  stress  from 
the  neutral  axis  outwards,  or  the  law  of  the  increments  of  stress  correspond- 
ing to  equal  increments  of  deformation,  is  exactly  that  represented  by  the 
stress-diagram,  since  here  we  have  the  increments  of  stress  shown  for  equal 
increments  of  deformation.  Hence  it  follows  that  if  ft  is  the  stress  on  the 
extreme  fibre  of  the  bent  beam  on  the  tension  side  the  stresses  on  all 
other  fibres  on  the  tension  side  are  truly  indicated  by  the  lengths  of  the- 
corresponding  ordinates  on  that  side  of  the  neutral  axis,  when  the  position 
of  the  stress  ordinate/  in  the  stress-diagram  is  taken  as  the  position  of  the 
extreme  tension  side  of  the  beam,  and  the  origin  in  that  diagram  is  taken 
as  lying  on  the  neutral  axis  of  the  beam.  Evidently  the  same  argument 
would  apply  to  the  compression  side. 

35.  Distribution  of  Stress  and  Position  of  the  Neutral  Axis  at  Ruptuie. 
—In  a  brittle  material  like  stone  or  cast  iron,  failure  occurs  on  the  tension 
side;  while  in  the  case  of  wood,  failure  usually  occurs  first  on  the  compres- 
sion side  of  the  beam.  The  diagrams  shown  in  Fig.  28  may  fairly  be  taken 
as  representing  the  facts  in  the  case  of  cast  iron,  and  those  in  Fig.  29  in  the 
case  of  timber.  Since  timber  is  much  stronger  in  tension  than  in  compres- 
sion, it  fails  first  on  the  compression  side.  Furthermore,  after  the  fibres 
have  buckled,  or  broken  down,  in  compression,  they  are  able  to  support  only 
about  three  fourths  as  much  of  a  load  as  before,  so  that  the  compression 
stress-diagram  has  the  peculiar  form  shown  in  the  accompanying  figure. 

At  failure,  therefore,  the  tensile  and  compressive  stresses  are  distributed 
over  the  section  in  a  manner  entirely  different  from  that  which  obtains 

*  See  Chap.  XXIII  for  complete  stress-dingrams  for  cast  iron  of  various  qualities. 


MATERIALS   UNDER  CROSS-BENDING  STRESS. 


51 


within  the  elastic  limit.  The  statement  made  in  Art.  25,  however,  regard- 
ing the  equality  between  the  sums  of  the  tensile  and  compressive  stresses 
must  still  hold,  as  this  is  a  mathematical  or  mechanical  necessity;  and  as 
this  total  stress  is  graphically  represented  by  the  area  of  the  stress-diagram 


FIG.  29. 

shown  on  the  sections  of  the  beams  in  Figs.  28  and  29,  it  follows  that  these 
stress  areas  on  the  two  sides  of  the  neutral  axis  must  be  equal. 

Thus  in  the  case  of  timber,  for  instance,  the  neutral  plane  at  first  lies  in 
the  centre  of  gravity  of  the  cross-section,  but  after  the  material  has  begun  to 
crush  on  the  compression  side,  the  neutral  plane  rapidly  moves  towards  the 
tension  side  of  the  beam  and  often,  at  final  rupture,  it  lies  very  near  this  side, 
the  tension  stress  area  being  a  triangle  of  very  long  base  (stress  on  extreme 
fibre)  and  very  short  altitude  (distance  to  neutral  plane).  It  is  evident 
that,  although  the  beam  has  long  since  failed  in  compression,  if  it  be  con- 
tinuously deflected,  failure  must  ultimately  occur  also  in  tension.  When 
the  material  is  weaker  in  tension  than  in  compression  such  double  failure 
cannot  occur,  since  the  tension  failure  parts  the  body,  and  the  rupture  is 
complete.  Evidently  no  general  law  can  be  given  for  distribution  of  the 
stress  across  the  section  after  the  elastic  limit  has  been  passed,  other  than 
to  say  it  is  that  of  the  corresponding  stress-diagrams  of  that  material  in 
direct  tension  and  compression  respectively. 

36.  Moduli  of  Rupture  in  Cross-breaking. — Prom  the  facts  related  in  the 
preceding  article  it  is  evident  that  the  formulae  of  Articles  32  and  33  cannot 
apply  at  rupture,  and  that  if  the  breaking-load  be  used  for  computing  the 
so-called  ultimate  strength  of  the  material  in  pounds  per  square  inch  (the 
"modulus  of  rupture  in  cross-breaking/7  and  the  quantity  /"in  those 
formulas  when  P  is  the  breaking-load,  or  when  M  is  the  ultimate  bending 
moment),  the  result  obtained  as  the  value  of  /is  a  purely  fictitious  quantity, 
and  that  it  does  not  really  represent  any  actual  tensile  or  compressive  stress 
on  the  extreme  fibres  at  all.  It  may,  however,  be  called  the  "  modulus  of 
rupture  in  cross-breaking"  in  pounds  per  square  inch,  and  used  to  indicate 
the  strength  of  the  material  when  loaded  as  a  beam ;  but  it  must-  not  be  con- 
fused with,  or  assumed  to  have  any  fixed  relation  to,  either  the  tensile  or  the 
compressive  strength  of  the  material.  As  a  matter  of  fact  it  always  lies 
somewhere  between  these  two  latter  values,  but  it  does  not  have  any  uni- 


THE  MATERIALS  OF  CONSTRUCTION. 


versal  relation  to  them.  It  is  always  dependent  largely  on  the  form  of  the 
cross-section  of  the  beam,  as  to  the  concentration  of  material  near  the  neu- 
tral axis  or  near  the  extreme  sides.  Thus  the  elastic-limit  strength  of  a 
rolled  I  beam  can  be  very  closely  approximated  by  using  for /in  equation 
(5)  the  tensile  or  compressive  elastic-limit  strength  of  the  material  in  either 
tension  or  compression,  while  the  elastic-limit  strength  of  a  solid  round 
bar  could  not  be  determined  very  closely  by  so  doing.  Also  the  ultimate 
strength  of  a  cast-iron  beam  of  an  I-shaped  cross-section  could  be  deter- 
mined approximately  by  using  the  tensile  strength  of  the  material  for  the 
value  of  /  on  the  tension  side  of  the  beam  in  eq,  (5),  but  the  ultimate 
strength  of  a  round  or  square  cast-iron  bar  would  be  nearly  twice  as  much 
as  would  be  shown  by  the  use  of  eq.  (5)  if  the  tensile  modulus  of  rupture 
were  taken. 

37.  The  Distribution  of  Shearing  Stress  in  a  Beam. — (a)  The  Relation 
between  Shear  and  Bending  Moment  at  any  Section.  —  In  Fig.  30  assume 

any  two  adjacent  sections  dx  apart.  Let  the  total 
shearing  force  acting  here  be  S.  Call  the  bending 
moment  at  the  first  section  M,  and  that  at  the  other 
M'.  Assume  the  beam  to  be  cut  at  the  section 
where  the  moment  is  M9  and  the  left  portion  re- 
moved and  replaced  by  the  direct  tensile  and  com- 
pression stresses,  and  also  by  the  total  shear,  S. 
Then  it  is  evident  the  moment  at  the  adjacent 
section  is 

....     (10) 


M  M 


M  M 


But 


FIG. 


M'  -M=  dM, 


hence  we  have 
M'-M=dM=Sdx, 


or    o  — • 


dM 
dx' 


(11) 


That   is   to  say,  the  total  shear  on  any  transverse   section  of  a   beam  is 
equal  to  the  first  differential  coefficient  of  the  bending  moment. 
It  follows  from  this  that — 

(1)  Where  the  bending  moment  is  constant  the  shear  is  zero. 

(2)  Where  the  shear  is  zero  the  bending  moment  is  at  a  maximum 

or  a  minimum. 

(b)  The  Distribution  of  the  Shearing  Stress  across  any  Transverse  Sec- 
tion.— In  Fig.  31  take  two  transverse  sections, 
dx  apart,  as  before,  on  which  the  moments  are  M 
and  M'  respectively.  By  eq.  (5),  Art.  26,  we 
have  for  the  stresses  on  the  outer  fibres  at  these 
two  sections 


and 


MATERIALS   UNDER   CROSS-BENDING  STRESS.  53 

Also  for  any  horizontal  section,  as  cc1 ',  the  fibre  stresses  will  be 

P=f?L=%>       and      ,'  =  *£ 

The  breadth  of  the  beam  must  be  regarded  as  variable  to  obtain  a  gen- 
eral solution,  and  it  will  be  denoted  by  b,  a  variable  quantity. 

Now  the  total  shearing  stress  on  the  section  cc' ,  whose  area  is  b'dx,i&  the 
difference  between  the  total  direct  stress  on  a'c'  and  on  ac.  But  the  stress- 
on  ac  is 


A/17   ir      ^ 

X//i  /     bMyd 

pbdy  —     /          'T 
Jy>         1 


Similarly,  the  total  direct  stress  on  a'c'  is 


The  difference  is 


f'b(M'-  M)ydy  _     C^ldMydy. 
Jy  I  "Jt        7 


v' 

But  dM '=  Sdx  by  the  previous  article,  hence  we  have  at  last 

CyibSdxydy 
total  stress  on  plane  cc'  —    I         ~~f~~         .... 

t/  y* 

But  the  area  of  this  section  on  cc'  is   bdx.     Hence  the  intensity  of  the 
stress  on  this  plane  is  / 

c/  y* 


I  VlbSdxydy 
b'ldx" 


Now  S,  I,  and  b'  are  constant  for  any  given  beam,  transverse  section,  and 
:  plane  of  shear  cc'  ';  hence  these  quantities  can  be  removed  from  under  the 
integral  sign,  and  we  have 

Intensity  of  shearing  stress  at  any  point  in  a  beam,  distant  y  from  tlie 
neutral  axis,  is 


/*«/! 

Now   /     bydy  is  the  statical  moment  of  that  portion  of  the  cross-section 

of  the  beam  outside  the  line  cc'  on  which  the  shearing  stress  is  obtained, 
taken  about  the  neutral  axis;  hence  we  may  say: 

The  intensity  of  the  shearing  stress  at  any  point  in  the  cross-section  of 
a  beam  is  equal  to  the  total  shearing  stress  on  that  cross-section,  multiplied 
by  the  statical  moment  of  the  area  of  that  portion  of  the  cross-section  out- 
side the  longitudinal  plane  of  shear  in  question,  about  its  axis  in  the  neu- 


54  THE  MATERIALS  OF  CONSTRUCTION. 

tral  plane,  divided  by  the  product  of  the  moment  of  inertia  of  the  entire 
cross-section  into  the  breadth  of  the  section  at  that  point. 

This  applies  to  solid  sections  of  beams  of  all  possible  shapes. 

For  a  solid  rectangular  section  b  is  constant  and    /    bydy  =  ~(y*  —  yz). 

Jy 

Hence  for  this  case,  where  h  =  2ylt  and  b  —  b'  (a  constant),  we  have 


«•=§[(!)'  -/]-  1 


Hence  the  shear  at  the  extreme  sides,  where  y  —  -,  is  zero,  and  at  the 

fy 

neutral  axis 


That  is  to  say,  the  maximum  intensity  of  the  shearing  stress  on  a  solid 
rectangular  section  is  f  of  the  mean  intensity. 

It  is  evident,  also,  that  eq.  (14)  is  the  equation  of  a  parabola  with  it 

vertex  on  the  neutral  axis,  whic 

Beam  uniformly  loaded  .         ,         ,  -,  .         ,,    A , 

is  also  the  axis  of  the  curve.     0 


'eutral 


any  particular  longitudinal  plane 
also,  the  shearing  intensity  varie 


from  end  to  end  of  the  beam,  a 
the  total  shearing  stresses  on  th 
cross-sections  vary,  as  shown  i 

Fig.  32.     By  applying  equation  (14)  to  various  forms  of  cross-section  it  ca 

be  shown  that— 

1.  The  maximum  shearing  intensity  in  a  beam  of  a  solid  rectangula 
section  =  |-  the  mean  shear. 

2.  For  a  solid  circular  section  it  is  f  the  mean  shear. 

3.  For  I  beams  and  plate  girders  it  is  practically  equal  to  the  total  shea 
divided  by  the  area  of  the  web  portion  alone.* 

38.  To  Dimension  the  Cross-section  of  a  Beam. — (a)  For  Direct  Stress  O't 
the  Outer  Fibre. — If  the  beam  be  of  a  solid  rectangular  form  of  cross-section 

use  eq.  (G).     If  of  any  other  form,  use  eq.  (5)  and  evaluate  —  by  the  accom 

•J  \ 

panying  table,  if  the  form  be  one  there  given.  If  not,  it  will  be  necessar 
to  compute  the  moment  of  inertia.  If  the  form  be  irregular  or  unsym 
metrical,  it  may  be  best  to  obtain  the  moment  of  inertia  graphically.!  Ii 
the  case  of  unsymrnetrical  sections  the  neutral  axis  lies  at  different  distance 
from  the  outer  fibres  on  the  tension  and  compression  sides,  and  it  may  b< 

necessary  to  compute  both  of  them.     Since  f\  =  — jr-1,  it  is  evident  thes-- 

*  See  Modern  Framed  Structures,  Art.  130. 
\  Ibid.,  Art.  127. 


MATERIALS   UNDER   CROSS  BENDING  STRESS.  55 

stresses  per  square  inch  are  to  each  other  directly  as  the  distances  of  their 
fibres  from  the  neutral  axis.     Thus  in  the  case 
of  a  cast-iron  beam  the  cross-section  is  made 
larger  on  the  tension  side,  as  in  Fig.  33.     Here 
the  outer  fibres  on  the  compression  side  are 
much  farther  away  from  the  neutral  axis  than 
the  outer  fibres  on  the  tension  side,  and  hence  the  maximum  stress  in  com- 
pression is  much  greater  than  it  is  in  tension,  which  is  as  it  should  be. 
For  a  solid  rectangular  section  we  have 


M=M.  =        -,    or     bk"  =        ......     (16) 

Take  M—  maximum  bending  moment  on  the  beam,  in  inch-pounds, 
and  f  =  working  value  of  the  stress  on  the  outer  fibre.  This  gives  the 
value  of  bit*,  and  1}  and  h  can  now  be  chosen  at  pleasure,  conditioned  on 
Wf  being  equal  to  the  right-hand  side  of  the  equation. 

(b)  For  Shearing  Stress  along  the  Neutral  Axis.  —  Since  timber  is  very 
weak  in  shearing,  as  compared  to  its  strength  in  tension  and  compression, 
timber  beams  and  joists  of  ordinary  lengths  will  usually  fail  by  shearing, 
and  hence  they  should  be  dimensioned  to  safely  withstand  this  shearing 
action.  Lanza  shows*  that  the  shearing  strength  of  spruce  and  white-  and 
yellow-pine  beams  is  about  -fa  of  the  transverse  modulus  at  rupture,  but  he 
recommends  a  much  smaller  factor  of  safety  for  shearing  than  for  transverse 
rupture.  If  the  factor  of  safety  for  shearing  be  two  thirds  that  for  trans- 
verse strength,  we  would  have  the  working  stress  in  shearing  -fa  that  in 
cross-breaking.  In  order  to  show  what  length  of  wooden  beams  would 
require  dimensioning  for  shearing,  using  this  relation  of  working  stresses, 
we  have 

/=20?0      .........     (17) 

For  a  beam  loaded  at  the  centre 

e       W        ,     ,,      Wl 

S  =  —     and     M—  —  . 

ii  4 

For  a  beam  uniformly  loaded 

W  Wl 

S  =  —     and     M  =  —  . 

/w  O 

Also  from  (16),  for  cross-breaking, 

Wi*  -- 
and  from  (15) 


Applied  Mechanics,  4th  ed.,  p.  696. 


66  THE  MATERIALS  OF  CONSTRUCTION. 

For  a  beam  loaded  at  the  centre 


For  a  beam  uniformly  loaded 

QM       3   Wl 

bh-"T  ~-*T  ........  (20) 

From  (17),  (18),  and  (19)  we  find,  for  beams  loaded  at  the  centre,  they 
are  equally  strong  in  shearing  and  in  cross-breaking  when 


<»> 


and  for  beams  uniformly  loaded  they  are  equally  strong  in  these  two  ways 
when 

1    -  f  » 

•  — 


For  shorter  lengths  wooden  beams  are  weaker  in  shearing  than  in  cross- 
breaking.  Hence  we  have  the  following 

PROPOSITIONS. 

Wooden  Beams  in  Shearing  and  Cross-breaking. 

I.  For  a  centre   load   the  beam  should  be  dimensioned  for  a  shearing 
stress  wlien  the  ratio  of  length  to  height  is  less  than  one  half  the  ratio  of  the 
cross-breaking  to  tlie  shearing  working  stress. 

II.  For  a  uniformly  distributed  load  the  beam,  should  be  dimensioned 
for  a  shearing  stress  when  the  ratio  of  length  to  height  is  less  than  the  ratio 
of  the  cross-breaking  to  the  shearing  working  stress. 

Thus,  for  white-  and  yellow-pine  and  spruce  beams  we  may  take 

^  =  20.* (23) 

Whence 

All  pine  and  spruce  beams  should  be  dimensioned  for  shearing  failure: 

I 
For  concentrated  centre  load  ivhen        T  ^  10. 

•  (24) 

For  uniformly  distributed  load  'when  -^  <20. 

In  dimensioning  for  cross-breaking  use  equations  (19)  and  (20),  and 
for  shearing  use  equation  (18),  for  both  concentrated  and  distributed  loads. 
The  following  working  values  of /and  q0  may  be  used. 

*  Here  q0  is  not  the  true  shearing  resistance  of  sound  timber,  but  the  shearing  resist- 
ance of  large  beams  along  their  neutral  axis,  where  they  are  usually  season -checked. 


MATERIALS   UNDER   CROSS-BENDING  STRESS. 


57 


Species. 

Working  Values  of 
Cross-breaking 
Modulus  in  Pounds 
per  Square  Inch. 
(f) 

Working  Values  of 
Shearing  Modulus  in 
Pounds  per  Square 
Inch. 
(</o) 

White  pine  

1000 

50 

Long-leaf  Southern  yellow  pine 
Short-leaf  Southern  yellow  pine 
Norway  pine  

1600 
1400 
1000 

80 

70 
50 

Spruce  

1200 

60 

AVhite  oak           

1200 

100 

Red.  cypress  

1200 

90 

1000 

50 

Tables  of  working  loads  for  beams  of  all  these  species  of  different  lengths 
and  depths  are  found  in  Chapter  XXXII. 

DEFLECTION   OF   BEAMS. 

39.  Development  of  General  Formulae. — Let  Fig.  34  represent  that 
portion  of  a  bent  beam  which  is  tangent  to  a  horizontal  line,  the  beam  being 
bent  under  the  action  of  vertical  forces.  Take  the  origin  on  the  neutral 
axis  where  it  becomes  horizontal,  in  the  section  KL.  Then  any  other 


FIG.  34. 

section,  as  EC,  distant  x  from  KL,  and  originally  parallel  to  it,  now  makes 
an  angle  with  it  which  we  will  call  i.  These  two  planes  woulds  therefore, 
intersect  if  prolonged,  and  the  radius  of  the  curve  of  the  neutral  axis  OAB 
will  be  called  r.  Evidently  the  position  of  the  neutral  axis  in  the  plane  EC 
is  somewhat  below  the  axis  of  abscissae,  and  the  coordinate  of  this  point  A 
is  now  -f  x  and  —  y,  with  reference  to  the  origin  0. 

If  we  now  draw  the  line  GH  parallel  to  KL,  the  intercepts  in  the  outer 
fibres,  between  this  section  and  EC,  are  the  distortions  of  these  fibres  in 
the  length  OA  =  x.  This  distortion  may  be  called  a. 

To  investigate  the  law  of  +he  relative  changes  in  x  and  ?/,  take  another 
section,  FD,  distant  dx  from  EC.  Then  the  coordinates  of  B  with  reference 
to  A  are  +  dx  and  -»•  dy,  and  the  actual  length  along  the  neutral  axis  from 
A  to  B  is  ds  =  Vdx*  +  dy*.  Also  the  angle  between  EC  and  FD  is  di. 


58  THE  MATERIALS  OF  CONSTRUCTION. 

The  angle  i  is  also  the  angle  the  neutral  axis  at  A  forms  with  the  hori- 
zontal, or 


But  Ji  is  also  equal  to  — ; 


r      dxds' 


Evidently,  when  the  deflection  angle  i  is  small,  dx  is  practically  equal  to  ds, 
in  which  case  dxds  =  ifo;2;  whence  eq.  (23)  becomes 


(24) 


We  also  have  CAH  =  GAB  —i  —  — -  —  — ,  where  yl  is  the  distance  from 

the  neutral  axis  to  the  outer  fibre.     Also 

x       a  ,      1        ct 

£=—  =  -      and      -= (25) 

r      ?/,  r      xyl 

But  from  eq.  (2),  Chapter  I,  we  have  E  =  — ,  or  a  =  •*— .      In  this   case 

fx 

I  =  #?  and  p  =  f  =  stress  on  outer  fibre;  hence  we  have  a  =  -j=?. 

Also  from  eq.  (5)  we  have  M0  =  — ,     or    yl  =  ~— . 

Substituting  these  values  of  a  and  yl  in  eq.  (25),  and  also  M  for  M0, 
we  obtain 

1         a         fx    1    Jf        Jf 


^ 

r      xyv~  E'  x'fl~  El' 


Hence  we  have 


r 


These  are  the  fundamental  equations  for  use  in  all  problems  in  the 
deflection  of  beams.* 

The  relation  utilized  to  find  deflection  angles  and  movements  is 

d*ii       M  -,(dy\      Mdx 

»'  s^  ,*          *7 1       */    i    ___ 

~-v~~s  IZZ  ^-tV<       Ol 


*It  is  here  assumed  that  the  deflection  is  due  wholly  to  the  longitudinal  deformation 
of  the  fibres  from  bending  moment,  and  not  at  all  from  the  action  of  the  shearing  forces, 

which  is  substantially  correct  when  -  is  large  (see  Art.  46). 


MATERIALS   UNDER  CROSS-BENDING  STRESS.  59 

That  is  to  say,  the  change  in  the  angle,  or  the  amount  of  lending  effected  over 
a  certain  length  of  the  beam,  is  equal  to  the  bending  moment  into  this  length 
divided  by  EL  To  find  the  total  angle  or  total  amount  of  bending  in  a  given 
finite  distance,  therefore,  where  the  bending  moment  is  usually  changing 
at  all  points,  it  is  necessary  to  integrate,  or  sum  up,  the  infinitesimal  changes 
between  certain  limits  or  between  certain  transverse  sections.  Then  having 
found  the  law  of  the  curvature  of  the  beam,  the  deflection,  or  vertical  dis- 
placement at  any  point,  can  be  found  by  integrating  again  from  yf  to  y 
between  the  same  transverse  sections  of  the  beam.  The  only  difficulty  in 
this  work  is  encountered  in  finding  the  constants  of  the  first  integration. 
The  following  cases  are  the  most  common,  in  which  both  E  and  /are  taken 
as  constant  throughout  the  length'  of  the  beam.  Bending  moment  producing 
convexity  downwards  is  called  positive. 

4:0,  Beam  Fixed  at  One  End  and  Loaded  at  the  Other.— Here  we  have, 
for  the  value  of  the  bending  moment, at  any  sec- 
tion x,  Mx  =  —  P(l  —  x) ;  hence 


dx  ~ 

Integrating  this  between  the  limits  0  and  x,  FIG.  35. 

we  have 

tin  P    I  ^2\  flii 

3?  =  »  =  -  jj\fa  -  ^  j.     [+O=  0,  since,  for  x  =  0,  ^|  =  0.] 
Integrating  again  from  0  to  x,  we  have,  as  the  deflection  at  any  section, 
y=-  vr(l^r  ~  ?)•     [+0=0,  since,  f  or  x  =  0,  y  =  0.] 

JLJ  J.   \  /v  O  /  4 

To  find  the  maximum  angle,  and  also  maximum  deflection,  make  x  =  2, 
and  obtain 

PP 
max.  t'=*  —  9-^7; (28) 


PJ3 

max.  y  =  J  =  _  _ (29) 


41.  Beam  Fixed  at  One  End  and  Uniformly  Loaded. — Let  the  load  per 
unit  of  length  =  p.     Then  the  bending  moment 

at  any  section  x  is  Mx  =  —  ~ — - — '—;  hence  we 


A 


have 


FIG.  36.  dx 

Integrating  this  from  0  to  x,  we  have 

dy  _  .  pit  i       x*\  •  4y 

dx  2EI\  3  /*  '          '  '  dx  ~ 


60  THE  MATERIALS  OF  CONSTRUCTION. 

Integrating  again  from  0  to  x,  we  obtain,  as  the  deflection  at  any  section, 

<w      /7V          IT*         v*\ 

y  =  ~  all  VT  "  I  +  12)'    [+  c  =  °'  since>  for  x  =  °'  y  =  °'J 

Again,  we  find  the  maximum  angle  and  deflection  for  x  =  I,  where 

max.  i=-;  ........     (30) 


(31) 


42.  Beam  Supported  at  the  Ends  and  Loaded  at  the  Centre.  —  Let  the 
_________________  L  _________________  >      load   P   be   placed    at   the    centre. 

Then  the  moment  at  any  section  is 

Px 
Mx=  -—  ;  hence  we  have 

& 

FIG.  37.  d*y  '_  ,,.  _ 

—.  —  —  tlv  — 

dx 
Integrating  this  from  0  to  x,  we  have 

f  =  i=pf+c. 

dx  4 

Now  C  is  the  value  of  the  angle  i  at  the  origin,  where  x  =  0,  or  at  the 
lower  limit  of  the  integration;  in  other  words,  (7  is  the  value  of  the  angle 
we  started  with,  and  we  must  add  to  this,  algebraically,  the  changes-  of  the 
angle  from  0  to  x.  To  find  the  value  of  this  constant  we  must  pass  to  a 
point  where  the  value  of  the  angle  is  known.  In  this  case  we  know  this 

angle  is  zero  for  x  =  —  .     Hence   make  x  =  —  ,  for  which  -^  =  0,  and  we 

6  6 

PI* 

have  C  =  —  —  ^-.     Therefore 
lo 


dy  _  .  _  Px*  _Pl*  _Pt  ,       T\ 
dx  ~          ~T    ~  T6~  :~  4  r        4  J* 


Integrating  again,  we  have 


The  maximum  value  of  i  is  evidently  at  the  ends,  and  of  y  at  the  centre. 
Hence  we  have 

max.  t=  -  — ; (32) 


PI 
*  For  this  case  the  deflection  due  to  shear  is  -  .  _  .  .     (See  Art.  46.) 


MATERIALS    UNDER   CROSS-BENDING   STRESS. 


61 


43.  Beam  Supported  at  the  Ends  and  Uniformly  Loaded.— Let  the  load 

per  unit  of  length  =  p.     Then  the 
bending  moment  at  any  section  x  is 


P 


-y 

dx 


-(lx  -  x')dx. 


FIG.  38. 


Integrating  once,  we  have 

^__      P 


As  before,  for  x  =  -,          =  0;     hence     (7  =  - 


__ 
'  dx  2EI 

Integrating  again,  we  have 


5!      E!_n 
2         3       12/' 


y  = 


p     ix5  __  ^  _  ^ 


12 


—  1.     [+(7=0,  since,  for  a;  =  0,  y  =  0.] 


Max.  i  is  found  for  x  =  0,  and  max.  y  for  a;  —  -.     Hence 

& 


(34) 


(35) 


44.  More  Complicated  Cases  f  are  such  as  — 

(a)  Beam  supported  at  the  ends  and  loaded  at  any  point. 

(#)  Fixed  at  one  end  and  loaded  in  any  manner. 

(c)  Fixed  at  both  ends  and  loaded  in  any  manner. 

These  and  other  cases  are  treated  in  works  on  Applied  Mechanics,  and 
they  will  not  be  further  considered  here.  The  difficulty  in  such  cases  is  to 
•evaluate  the  constants  of  integration.  While  this  can  always  be  done,  the 
algebraic  reductions  are  long  and  tedious.  The  following  table  gives  all 
the  results  for  the  ordinary  cases  which  are  usually  needed  in  practice. 

45.  Table  of  Moments,  Stresses,  and  Deflections  of  Beams  having  Con- 
stant Moments  of  Inertia. 


*  For  this  case  the  deflection  from  shear  is  A—:.     (See  Art.  46.) 


f  For  an  excellent  design  of  a  home-made  apparatus  to  be  used  in  testing  the  correct- 
ness of  all  kinds  of  beam  formulae,  see  a  paper  on  this  subject  by  Prof.  James  L.  Greeti- 
leaf  in  Jour.  Franklin  Inst.  for  July  1895,  vol.  CXL.  D.  27. 


TllK  MATKUIMM  0V  VONtiTHUVTION. 


i   3 


3i* 


'.'.  '  '•'• 


: 

S 

: 


tf 


<O  CO 


i      i 

H     H 

"  j 


55 
•I- 

9 

I 


i       i 


* 


MATKH1ALS  IWDMIt  V110BB-BB1ND1NQ 


+ 

& 


*'       ~1 


•/;' 


/ 


sr1          i 


A        II 

H  >: 


64 


THE  MATERIALS  OF  CONSTRUCTION. 


03  P 


I 

CO  Ir^ 


CO 


•s 


IB 

Sit 


8  =  0 

II 


ftJ  ^        flfe 

W  0        w       ^  lo 

V         II         A         11 


«  +     "S 


cS 


cs  a  ^ 

O  S  "O 

'-CO  ^ 

I1  ^ 


V       II       A 


«g 

I 

01 

S 


I     I 


V       II    A 


a 


MATERIALS    UNDER   CROSS-BENDING  STRESS. 


65 


*B 

II 


liS-* 

Si 


II        II 

3»  ^ 


*   !>? 


0,100 

I 


THE  MATERIALS  OF  CONSTRUCTION. 

46.  Deflections  from  Shearing  Forces.—  For  short  beams  it  is  necessary 
to  take  into  account  the  shearing  forces  also.  Since  the  modulus  of 
elasticity  in  shearing  is  the  ratio  of  the  shearing  stress  to  the  angular 
distortion  (transverse  distortion  per  unit  of  length,  since  the  angle  is  equal 
to  its  tangent),  we  may  say  that  for  a  distance  along  the  beam  of  dx  where- 

A'* 

the  shearing  stress  per  unit  area  is  s  =  —  r  -,  the  differential  deflection  from. 

j± 

shear  is 


(36) 


To  integrate  this  we  have  to  express  8  and  A  as  functions  of  x.  The 
cross-section,  A,  will  be  assumed  as  constant,  and  for  a  concentrated  load 
8  is  also  constant  and  equal  to  the  supporting  force  on  that  side  of  the- 
load.  For  a  uniformly  distributed  load  8  is  equal  to  the  algebraic  sum  of 
the  forces  on  one  side  of  the  plane  of  shear,  which  here  must  be  taken 
normal  to  the  deflection.  Thus  for  any  section  distant  x  from  the  end  of 

p 
the  beam  we  have  for  a  concentrated  load  at  the  centre  8  =  —  ,  a  con- 

/v 

stant,  while  for  a  beam  uniformly  loaded  (supported  at  the  ends  in  both 
cases)  S  =  ~-px=p(^--  xj. 

'  Using  these  values  in  eq.  (36),  we  have  for  the 

Deflection  of  a  learn  from    shear  when    supported  at    its    ends    and 
loaded  at  the  centre, 

Ys  =  ZETAX>   °r  at  C6ntre  As  =  4^1  .....     <37) 

Deflection  of  a   beam  from    shear   when  supported  at  its   ends  and 
uniformly  loadedt 


or 

ys  =  -J-—1—  —  —  \     or  at  centre    As  =  -  *      .    .     .    .     (38) 

Hence  the  total  deflections  at  the  centre  for  these  two  cases  are 

A  =  P(  l*     ,     M 
•  Us-Si  ^  4^^y 


and 

5r 


r         z2    \ 

LE/+^Z> (40> 


*  Assuming  also  that  the  shearing  stress  is  uniformly  distributed  over  the  cross- 
section. 


MATERIALS   UNDER  CROSS-BENDING  STRESS.  67 

for  beams  supported  at  the  ends  and  loaded  with  a  single  concentrated  load 
P  at  the  centre,  and  with  a  uniformly  distributed  load  of  p  per  unit  of 
length,  respectively. 

For  the  metals  take  E$  =  \E,  while  for  wood  take  E,  =  \E.  The 
fibrous  character  of  wood  may  explain  the  apparent  anomaly. 

For  solid  rectangular  wooden  beams,  therefore,  we  have 

For  load  at  centre,  from  (39),  making  E8  =  \E,  and  —r-=  ——  —  -  —  -, 

A.       J.        L£    JL 


and 

For  beam  uniformly  loaded,  from  (40), 


These  equations  show  that  when  a  rectangular  wooden  beam  loaded  at 
the  centre  has  a  length  less  than  seven  times  the  height,  the  deflection 
from  shear  is  more  than  ten  per  cent  of  the  total  deflection,  while  for  such 
a  beam  uniformly  loaded  the  deflection  from  shear  exceeds  ten  per  cent  of 
the  total  when  the  length  is  less  than  about  six  times  the  height. 

47.  Determination  of  Young's  Modulus  of  Elasticity  from  Bending- 
Tests.  —  Since  E  enters  in  all  the  expressions  for  deflection  of  beams,  it  is 
evident  that  it  may  be  found  from  a  bending  test  where  all  the  dimensions, 
loads,  and  deflections  are  observed.  Thus  for  a  beam  of  uniform,  solid, 
rectangular  cross-section,  supported  at  the  ends  and  loaded  at  the  centre, 
we  should  have,  from  eq.  (33),  for  a  long  beam  where  deflection  from 
shearing  forces  could  be  neglected, 


Since  in  testing  a  beam  the  stress  on  the  extreme  fibre  is  also  desired,  the 
i  last  form  of  this  equation  may  be  useful  in  case/  is  also  to  be  computed. 
However,  this  value  of/  must  be  inside  the  elastic  limit  in  order  to  use  it 
in  computing  E. 

It  is  best  to  measure  a  series  of  coincident  loads  and  deflections,  and 
plot  them  as  in  Pig.  49,  then  draw  a  tangent  to  the  curve  at  the  origin 
and  use  this  in  finding  E.  Thus  the  tangent  line  OA  is  used  for  comput- 
i  ing  E,  and  the  coordinates  of  any  point  on  this  line  may  be  taken.  It  is 
convenient  to  take  a  point  representing  a  deflection  of  unity.  On  this 
curve  this  corresponds  to  a  load  of  6250.  The  dimensions  of  the  beam 
were  I  —  140  in.,  I  =  4.02  in.,  h  =  8,04  in.,  and  the  material  was  long-leaf 


€8  THE  MATERIALS  OF  CONSTRUCTION. 

yellow   pine    (Pinus  palustris}.      Using    the   second   form  of  eq.   (43) 
we  have 

.  Q  nis  =  2,070,000  pounds  per  square  inch. 


The  maximum  load  was  13,500  pounds,  from  which  we  find,  by  eq.  (6) 
tlie  computed  maximum  stress  on  the  outer  fibre  to  be 

f  —  TT^J  =  p-  jj-j  =  10,000  pounds  per  square  inch. 


15000 


10000 

'      1 

I 

5000 


1  Deflection  2  in  inches  3 

FIG.  49. 

The  elastic-limit  load  might  be  taken  as  9000  pounds,  whence  the  fibre- 
stress  at  this  limit  would  be 

3  X  9000  X  140 
-  2  X  4.02  X  8.04-  =  73°°  ^  ^  ^are  inoh' 

48.  The  Rational  Designing  of  Flitched  Beams.* — A  flitched  beam  is  one 
composed  of  two  sticks  of  timber  enclosing  between  them  a  wrought-iror 
or  steel  plate  of  the  full  length  of  the  sticks,  these  three  members  beinf 
rigidly  bolted  together,  preferably  along  the  neutral  plane,  in  such  a  waj 
that  they  will  act  as  one  solid  member  when  deflecting  under  a  load.  Ir 
order  that  these  two  materials  may  come  to  their  working  stresses  simul 
taneously,  the  iron  or  steel  plate  should  always  be  of  less  depth  than  thai 
of  the  timber. 

To  find  the  relative  depths  of  steel  (or  wrought  iron)  plate  and  tht 
timber  sides  in  order  that  they  shall  come  to  their  working  stresses  at  th< 

*  This  problem  is  introduced  here,  not  because  it  is  very  common  or  important  ii 
itself,  but  because  it  is  a  good  type  of  composite  systems  and  illustrates  the  methoc 
of  analyzing  such  systems. 


MATERIALS   UNDER   CROSS-BENDING  STRESS.  69 

same  time,  we  must  utilize  the  principle  that  when  two  or  more  members 
jointly  carry  a  single  load,  they  share  this  load  in  direct  proportion  to  their 
relative  rigidities.  The  rigidity  of  a  beam  is  the  inverse  of  its  flexibility, 
and  the  flexibility  is  measured  by  the  deflection  under  a  given  load.  Hence 
the  rigidity  will  be  measured  by  the  reciprocal  of  the  deflection.  The 
equation  representing  the  deflection  of  a  solid  rectangular  beam,  in  terms 
of  the  stress  on  the  outer  fibre,  is,  from  eq.  (33),  since 

I  PI 

M  =  -fbh2  —  -  -  for  a  load  P  at  the  centre. 
o  4 

pr  1 

~ 


•  But  since  the  rigidity  is  measured  "by  the  reciprocal  of  the  deflection, 
we  have  as  a  measure  of  the  rigidity  of  a  rectangular  beam,  in  terms  of  the 
stress  on  the  outer  fibre, 


5  =  rigidity  = -^  =  ^ (45) 

_/  /£ 

We  may  now  write  the  proportion: 

Deflection  of  the  t  deflection  of  the    t  the  rigidity  of  e  the  rigidity  of 
wooden  beam  steel  plate  the  plate  the  beam, 

or 


But 


Hence  we  have  for  a  flitched  beam,  in  which  Aw  —  As, 
Aw      Rs       Eshsfw 


A    - 

As  •  :  R   -.  R 

,   or     4-  =  * 

(46> 

Rs 

As        R: 
W«       EJisfw 

(47> 

(48) 


where  Rw  =  rigidity  of  the  timber  sides; 
Ra  =  same  for  the  steel  plate; 
Aw  =  deflection  of  the  timber  sides; 
As  =  same  of  the  steel  plate; 
Ew  —  modulus  of  elasticity  of  timber  =  from  1,000,000  in  white  pine 

to  1,800,000  in  long-leaf  yellow  pine; 

Es  =  modulus  of  elasticity  of  wrought  iron  and  steel  =  28,000,000; 
P  =  total  load  on  flitched  beam ; 
Pw  =  load  carried  by  the  timber  sides; 
P8  =  same  for  the  steel  plate; 
/«,  =  working  fibre-stress  for  timber  =  from  1000  in  white  pine  to- 

1800  in  long-leaf  yellow  pine; 
/8  =  same  for  steel  =  12,000  to  18,000  pounds  per  square  inch; 


70  THE  MATERIALS  OF  CONSTRUCTION. 

liw  =  depth  of  the  timbers  in  inches; 

hs  =  same  for  the  steel  plate; 

bw  =  total  thickness  of  both  timbers  in  inches; 

bs  =  same  for  the  steel  plate. 

From  eq.  (48)  we  may  derive  many  important  relations: 
(a)   To  find  the  relative  depths  of  steel  plate  and  wooden  learns  to  give 
simultaneous  working  stresses  in  each.     Eq.  (48)  may  be  written 


Example  :  Let  Es  =  28,000,000,  Ew  =  1,400,000,  fs  =  16,000,  /w  =  1600; 
then 

h»  _    28,000,OOOJ<_1600_  __  9 
1TS  ~  1,400,000  X  16,000  ~"  ~* 

That  is  to  say,  the  wooden  sides  must  be  twice  as  deep  as  the  steel  plate, 
regardless  of  their  respective  thicknesses,  in  order  to  give  a  working  stress- 
in  the  \vooden  sides  of  one  tenth  that  in  the  steel  plate. 

(b)   To  find  the  relative  stresses  on  the  outer  fibres  when  the  plate  is  of' 
the  full  depth  of  the  timber  sides.     We  now  put  eq.  (48)  in  the  form 


/KAX 
fs        E  ......     (50) 

Using  the  same  values  of  fias  above,  and  making  hw  =  hs,  we  have 

.U  _  Ew  _  1 
fs       El  ~  20' 

Hence  when  the  steel  or  iron  plate  has  the  full  depth  of  the  wooden  sides, 
the  stress  in  the  outer  fibres  of  the  timber  is  only  one  twentieth  that  in  the 
plate.  This  does  pretty  well  for  a  white-pine  and  steel  combination. 

But  in  the  case  of  white  pine  we  should  not  take  Ew  higher  than 
1,000,000.  Hence  we  have  for  white  pine  and  steel  of  equal  depths 

fw_E»L_    1,000,000         1 
fa       E8        28,000,000  ~~  28' 

That  is,  the  maximum  stress  in  the  timber  is  only  ^  that  in  the  steel  plate. 
For  an  elastic  limit  of  steel  of  40,000  pounds  per  square  inch  we  may  have 
a  working  fibre-stress  of  20,000  pounds  per  square  inch.  This  would  give  a 
fibre-stress  of  700  pounds  per  square  inch  in  the  timber  sides,  which  is- 
hardly  a  sufficiently  high  working  stress  for  white  pine.  All  these  conclu- 
sions are  quite  independent  of  the  relative  thicknesses  of  plate  and  sides. 

To  find  what  part  of  the  total  load  P  is  carried  by  the  timber  sides  and 
by  the  steel  plate  respectively,  we  may  let  Pw  and  Ps  represent  these  loads, 
so  that  Pw  -f  Ps  =  P.  Also  the  total  load  P  divides  itself  between  the 
parts  in  proportion  to  their  respective  rigidities,  these  rigidities  being  now 


MATERIALS   UNDER  CROSS-BENDING  STRESS.  71 

taken  as  the  reciprocals  of  the  deflections  when  expressed  in  terms  of  the 
equal  loads  W  instead  of  fibre-stresses.     From  eq.  (44)  we  have 

Rs  =  -T  =     pi S     and     Rw  =  -p  = 

" s  -L si  ^W 

whence  we  have 

P          7?  F  J 

ft  =  t  =  fi ^ 


(53) 


But  for  solid  rectangular  sections  /=  -fabh*',  hence  we  have 

P9 


Pw       Ewbwliw 
Jut  Pw  =  P  —  Ps,  which  substituted  in  (51)  and  reduced  gives 


P>  =  JOIO (54> 

Similarly, 


(55) 


Thus  if  the  depths  and  thicknesses  of  the  plate  and  of  the  timber  sides  be 
Inown,  the  parts  of  the  total  load  which  they  will  carry  can  be  found  from 
Iquation  (54)  or  (55),  or  their  relative  values  may  be  found  at  once  from 
Iquation  (53). 

EXAMPLE:  Dimension  aflitclied  learn  24  feet  long  to  carry  a  distributed 
\oadof2000  Ibs.  per  foot. 

Assume  a  depth  of  timber  sides  of  16  inches,  and  let  the  plate  be  the 
all  depth  of  the  timbers.  If  we  use  "long-leaf"  pine,  we  may  take 
?„,  =  1,400,000,  while  Es  =  28,000,000  for  the  steel  plate.  Eq.  (50)  now 

/•  -• 

fives  us  •—  =  — .     That  is,  the  maximum  fibre-stress  in  the  timber  sides  is 
js      ~u 

ne  twentieth  that  in  the  steel  plate.     We  will  also  assume  the  plate  to  be 
inch  thick.     If  it  is  stressed  to  20,000  Ibs.  per  square  inch,  the  load  it 
lone  will  carry  is  found  from  eq.  (G).     Thus 

Ms  =  ~  =  M0='f^~>     or     A  =  12,000  Ibs.,  nearly. 

|v 

;  ^is  leaves  36,000  pounds  to  be  carried  by  the  timber  sides. 

•  But  when  the  stress  in  the  plate  is  20,000  pounds,  that  in  the  timber  sides 
5  but  1000  pounds.  Hence  we  must  now  find  the  combined  breadth  of  the 
wo  sides  to  carry  36,000  pounds  with  this  fibre-stress.  Here  again  we  have 

Mo=f^^,     or    bw  =  l^-t  =  30  inches,  nearly. 

O  *±Jwtlw 


72  THE  MATERIALS  OF  CONSTRUCTION. 

As  this  thickness  is  out  of  the  question,  we  might  double  the  thickness 
of  the  steel  plate,  making  it  1  inch,  when  it  will  carry  24,000  pounds,  leaving 
24,000  pounds  for  the  timber  sides.  This  would  reduce  them  to  20  inches 
in  width,  or  two  sticks,  10  in.  by  16  in.  each. 

If  it  were  practical  to  obtain  timbers  18  inches  deep,  they  would  serve 
the  purpose  much  better.  (The  student  might  redirnension  the  beam  on 
this  assumption.) 

It  is  evident  from  the  above  that  there  is  no  economy  in  combining  iron 
and  wood  in  this  manner.  An  iron  or  steel  I  beam  or  a  plate  girder  should 
always  be  used  in  such  a  case  when  this  is  practicable.  The  problem  has- 
been  inserted  here  as  a  valuable  exercise. 

49.  Steel  and  Concrete  in  Combination. — It  is  now  common  to  employ 
steel  wires  or  bars  to  strengthen  the  tension  sides  of  concrete  beams.  To 
analyze  this  case  it  is  necessary  to  know  the  modulus  of  elasticity  of  the; 
particular  concrete  employed,  and  at  the  age  when  its  working  strength  is-* 
first  required.  This  property  of  concrete  has  seldom  been  observed  (see; 
Chapter  XXX),  but  for  good  Portland-cement  concrete  it  may  be  taken  at: 
1,000,000.  For  cinder  concrete,  such  as  is  used  in  fire-proof  flooring  int 
buildings,  it  is  very  much  less,  possibly  not  over  100,000. 

Kef  erring  again  to  the  general  proposition  that  in  composite  structures  the' 
load  divides  itself  between  the  systems  in  direct  proportion  to  their  relative- 
rigidities,  we  conclude  that  for  like  areas,  similarly  placed,  the  rigidities  are' 
to  each  other  as  their  moduli  of  elasticity.  Since  the  modulus  of  elasticity 
of  steel  is  28,000,000  and  of  the  concrete,  say,  1,000,000,  it  follows  that  one 
square  inch  in  section  of  steel  resists  for  equal  deformations  as  much  as  28- 
square  inches  of  concrete  similarly  placed.  To  find  the  resistance  of  the- 
combined  material,  therefore,  substitute  an  amount  of  concrete  for  the  steel  1 

wire  or  bar  equal  to  twenty-eight  times- 
its  cross-section,  adding  this  in  the  hori- 
zontal plane  of  the  steel  bar,  and  then 
treat  this  new  form  of  section,  as  shown 
in  Fig.  50,  as  an  actual  beam  of  concrete. 
By  finding  its  moment  of  inertia,  the 
strength  of  the  beam,  when  the  concrete* 
fails  by  cracking  on  the  tension  side,  mayi 


FIG.  50.— Steel  and  Concrete  in          ,       «  fl 

Combination.  be   found    from    the  equation   M9  ==  ^-, 

where/  is  the  ultimate  tensile  strength  of  the  concrete  ;  /is  the  moment  of1 
inertia  of  the  transformed  section;  yl  is  the  distance  from  the  neutral  axis> 
of  this  section  to  the  tension  side  of  the  beam ;  and  M0  is  the  moment  of 
resistance  of  the  actual  beam  when  the  concrete  cracks.* 

*  For  a  discussion  of  the  case  where  the  concrete  cracks  and  the  elastic  limit  of  the 
steel  bar  is  reached,  as  well  as  for  the  case  where  the  concrete  cracks  on  the  tension  side 
and  then  fails  in  compression  because  of  the  strength  of  the  steel  bar,  including  also  the 
case  here  treated,  see  an  article  by  the  author  in  Engr.  News,  Jan.  3,  1895,  p.  10. 


MATERIALS   UNDER  CROSS-BENDING  STRESS.  72a 

If  b  =  breadth  of  concrete  beam, 
h  =  height     " 
a  =  area  of  steel  bar, 

77T 

A  =  substituted  equivalent  area  of  concrete  =  a  ~9 

Es  =  modulus  of  elasticity  of  steel, 
Ec  =          "       "          "         "  the  concrete  used, 
e  —  distance  from  centre  of  beam  to  centre  of  bar, 
d—         "          "          "       "      "       "  new  neutral  axis, 
?/,  =         "          "   neutral  axis  to  tension  side  of  beam, 
yt  =  "         "      "  compression  side  of  beam, 

ft  =  stress  on  outer  portion  of  the  concrete  on  the  tension  side, 
/«=        "      "       "         "         "     "          "         "     "     compression  side, 
/  =  moment  of  inertia  of  the  transformed  cross-section, 

C*   -I/" 

/0  =  stress  on  outer  portion  of  beam  if  no  steel  bar  were  used  =  ~t, 

Oil' 

m  —  —  .  -jrf,  used  for  convenience  (but  is  in  fact  the  ratio  of  the  lon- 
a    tis 

gitudinal  rigidity  of  the  beam  to  that  of  the  steel  bar), 
then  we  have 


Tensile  stress  on  concrete  at 
bottom 


Compressive   stress  on    con-  |  _  /.  _  My9  __ 

crete  at  top  j  ~~  *c  ~     /    ~"  ^° 


1  +  TO+12_ 


If  the  steel  bar  be  a  flat  plate  and  this  be  placed  at  the  bottom  of  the 
beam,  but  buried  in  the  concrete,  then  e  —  —  and  we  have 

Tensile  stress  on  concrete  at  bottom  =  ft'  =  fA — - — -\          (A') 

'  °  \m-\-  4:) 

and  similarly 

Compressive  stress  on  concrete  at  top  =//  =/„(—      -r).  (B') 

If  the  steel  rod,  or  plate,  be  removed  still  farther  from  the  body  of  the 
concrete,  by  placing  it  in  the  lower  side  of  a  projecting  rib  of  concrete,  then  e 

becomes  greater  than  -.     Equations  (A)  and  (B)  will  still  apply  to  this  case, 

6 

merely  using  the  true  values  of  e  and  h,  not  counting  the  projecting  rib  as 
any  part  of  the  concrete  beam.  Thus  if  a  concrete  floor  4  inches  thick  be 
supported  by  ribs  every  two  feet,  in  the  bottoms  of  which  are  steel  rods  1 


726  THE  MATERIALS  OF  CONSTRUCTION. 

inch  square,  so  placed  as  to  be  10  inches  below  the  centre  of  the  concrete 
floor,  then  from  equations  (A)  and  (B)  we  have 

f>  =    -f"  =  °-007/«  and  f'  =    '•  =  °- 


f       GM       M 
where  /0  =  m- =  OQT- 


If  any  particular  ratio  of  compressive  to  tensile  strength  of  the  concrete 

is  to  be  developed,  we  may  impose  the  condition^  =  &;  whence  for  the  steel 

/* 
placed  at  the  bottom  side  of  ttye  beam  we  have,  from  equations  (A')  and 


whence,  iox      = 


-—  -    —     \j    —  9  if    —  __     —  —     _ 

ft  m  a  Es       Jc  —  1 

-  V)EC 


Thus  if  ^  =  5,  we  have,  for  ~  =  —  ,  a  =  j|. 

That  is  to  say,  if  the  steel  plate  covered  the  entire  base  of  the  beam,  it 
would  have  to  be  -fa  as  thick  as  the  concrete  and  steel  combined  to  satisfy 
this  condition,  it  being  assumed  in  this  and  all  former  cases  that  the  con- 
crete does  not  crack  on  the  tension  side.  Evidently  it  is  impracticable  to 
develop  the  full  compressive  strength  of  the  concrete  by  this  construc- 
tion, on  condition  that  the  concrete  is  to  remain  unbroken  on  the  tension 
si'de. 

To  find  the  total  stress  in  the  steel  bar,  we  assume  it  to  stretch  the  same 
as  the  parts  of  the  concrete  beam  adjacent  to  it;  hence  for  any  given  position, 
distant  e  from  the  centre  of  the  beam,  we  have 


Total  stress  on  steel  bar  =  ^(e  —  d)-^  a  =  -     -  =j          (D) 

/J  l  +  «  +  l»jf 

If  e  —  --,  this  becomes,  for  the  bar  at  the  bottom, 
Z 

Total  stress  on  steel  lar  at  bottom  ~4("ir 

ill  ~\~  t\   fv 

For  this  case  the  tensile  stress  in  the  steel  rod,  in  pounds  per  square 

7~r  Tji 

inch  is  -W1/,,  or  it  is  -^  times  as  much  as  that  in  the  concrete  adjoining  it. 
H/c  litc 

This  stress  in  the  steel  bar  can  never  be  more  than  from  2000  to  5000 
pounds  per  square  inch  in  rock  or  gravel  concrete,  but  in  cinder  concrete  it 
would  be  very  much  more.  To  utilize  the  strength  of  the  steel,  therefore, 
in  rock  concrete,  it  is  necessary  either  to  allow  the  concrete  beam  to  crack 
on  the  tension  side  or  to  remove  the  steel  bars  to  the  lower  portions  of 
projecting  ribs. 


MATERIALS   UNDER   CROSS-BE2VD1NG   STRESS.  73 

50.  Approximate  Determination  of  the  Strength  of  Flat  Plates  under 
formal  Forces.* — (a)  Flat  Circular  Plate  Supported  at  the  Circumference 
and  Uniformly  Loaded. — Assume  a  diametral  strip  1  in.  in  width  to  be  loaded 
over  its  full  width  at  the  ends,  but  the  loaded  surface  to  reduce  to  a  zero 
width  at  the  centre,  this  load  to  be  p  Ibs.  per  square  inch.  The  total  load 

on  the  strip  will  then  be  pr,  and  each  end  support  will  be  -— .     The  bending 

moment  at  the  centre  will  be 

pr          pr             pr* 
M0  =  —  .  r  — —  .  f  r  -  -  — (56) 

But  for  a  solid  rectangular  section  we  have 

M0  =  ^fblf,     or,  for  #,  =  1; 


whence 

h  =  r\l- (58) 

where  h  —  thickness  of  plate  in  inches; 
r  =  radius  of  plate         "        "     ; 
f  =  stress  in  extreme  fibre  in  pounds  per  square  inch; 
p  =  pressure  on  plate  in  "        "         "        " 

From  a  very  elaborate  analysis,  Prof.  Grashof  finds  for  this  case 


(b)  Square  Flat  Plate  Supported  at  the  Periphery  and  Uniformly  Loaded. 
—  Since  the  corners  are  more  distant  from  the  centre  and  therefore  carry  a 
less  proportion  of  the  load,  we  may  assume  that  the  opposite  sides  act  inde- 
pendently, so  far  as  the  bending  moment  at  the  centre  is  concerned.  On 
this  assumption  the  plate  may  be  regarded  as  supported  at  two  sides  only 
and  loaded  with  one-half  the  actual  load,  whence  we  have 

MQ  =  ^pW=^fbh\    ........     (59) 

or 


1/4, 


*  =  11  =0.6111,   ......     (60) 

y  /  / 

where  I  =  length  of  one  side  of  the  square  plate. 

(c)  Same  Cases  when  the  Plates  are  Fixed  in  Position  at  their  Periph- 
eries. —  Since  the  maximum  bending  moment  on  a  beam  fixed  at  the  ends 
and  uniformly  loaded  is  only  J  that  of  a  beam  supported  at  the  ends  and 

*  These  proximate  solutions  are  offered  as  illustrative  of  simple  approximate  methods 
which  may  often  be  applied  to  very  complicated  problems  of  this  class. 


74  THE  MATERIALS  OF  CONSTRUCTION. 

similarly  loaded,  we  may  assume  the  same  relations  would  hold  here,  thus 
giving  for  a  circular  plate,  rigidly  held, 


For  a  square  plate,  rigidly  held, 


or 


(d)  For  Elliptical  and  Rectangular  Plates.  —  Here  the  plate  fails  by 
cracking  along  its  greater  axis;  and  since  the  deflection  of  a  beam  for  a 
given  load  is  as  the  cube  of  the  length,  it  is  evident  that  the  ends  carry  but 
a  small  part  of  the  total  load.  Where  the  longer  axis  is  more  than  twice  the 
shorter  one,  we  may  neglect  these  end  bearings  entirely  when  we  have  the 
case  of  a  flat  plate  supported  at  two  opposite  sides,  which  then  becomes  a 
simple  beam:  and  this  is  the  proper  assumption  to  make  in  such  a  case. 
Making  this  assumption,  and  calling  b  the  smaller  dimension  of  the  opening, 
we  have 


Prof.  Bach  gives  for  this  case 


where  0  is  somewhere  between  f  and  1. 

When  the  longer  axis  is  about  1J  times  the  shorter,  as  is  common  with 
manhole-  covers,  assume  that  f  of  the  total  load  is  carried  at  the  sides,  thus 
giving,  from  (64), 


f-  or    A  - 

-*'  4  K"  -  4r  /" 


CHAPTER  VI. 
THE  RESILIENCE  OF  MATERIALS. 

51.  Resilience  Defined. — Resilience  is  literally  the  springing  back  of  a 
deformed  body  after  the  deforming  force  has  been  removed.  As  used  in 
mechanics,  however,  it  is  the  work  done  by  the  body  in  this  springing  back, 
which  is  the  same  as  the  work  done  on  the  body  in  deforming  it,  so  long  as 
this  is  inside  the  elastic  limits.  Beyond  the  elastic  limit  the  work  of 
deformation  always  exceeds  the  work  given  back  by  the  body.  The  body 
then  does  not  fully  recover  its  initial  position,  shape,  or  dimensions. 
Sometimes  the  work  of  deformation,  whether  inside  or  beyond  the  elastic 
limit,  is  spoken  of  as  the  resilience,  but  this  is  improper.  The  resilience 
proper  is  the  amount  of  work,  or  energy,  in  foot-pounds,  ivhich  can  be  stored 
in  an  elastic  bod?/,  up  to  a  given  stress  per  square  inch,  and  which  can  be 
given  out  again  by  the  body  as  useful  work,  if  desired*  That  portion  of  the 
energy  spent  in  deforming  the  body  but  not  given  back  as  resilient  work  is 
spent  in  permanently  deforming  the  body,  by  causing  the  particles  to  move 
or  slide  over  each  other,  thus  developing  heat.  The  elastic  deformation 
of  a  body  does  not  develop  heat.  Since  work  is  measured  by  a  force 
acting  over  a  distance,  the  work  of  deformation  may  be  measured  by 
the  product  of  the  deforming  force  into  the  distance  through  which  it 
acts.  But  the  deforming  force  is  zero  at  first  and  increases  uniformly  as 
the  deformation  increases  (inside  the  elastic  limit);  hence  the  total  work 
done  in  deforming  a  body  is  the  average  value  of  the  force  into  the  total 
deformation.  Since  the  force  increases  uniformly  with  the  deformation,  its 
average  value  is  always  one  half  its  final  value  (inside  the  elastic  limit),  so 
that  the  ivork  of  deformation,  or  the  energy  stored  in  the  body,  is  one  half 
the  product  of  the  final  force  (or  resistance},  into  the  deformation.  Inside 
the  elastic  limit  the  stress-diagram  (for  all  kinds  of  stress)  is  a  straight  line, 
and  here  also  the  resilience,  or  work  given  back,  is  equal  to  the  work  of 
deformation.  Hence  the  elastic  resilience  is  equal  to  the  triangular  area  of 
the  stress-diagram,  included  between  this  curve,  the  axis  of  deformation, 
and  an  ordinate  parallel  to  the  axis  of  loads,  to  the  extremity  of  the  locus 
developed.  As  similar  areas  are  to  each  other  as  the  squares  of  their  like 

*This  is  the  sense  in  which  Young  first  used  the  term  in  1807,  but  he  did  not  so 
clearly  define  it  since  he  assumed  bodies  to  be  perfectly  elastic  to  rupture. 

75 


76  THE  MATERIALS  OF  CONSTRUCTION. 

parts,  or  dimensions,  it  is  evident  that  the  elastic  resilience,  or  energy, 
stored  in  a  body  is  as  the  square  of  the  unit  stress  under  the  finals  load,  this 
unit  stress  being  equal  or  proportional  to  the  load  ordinate  in  the  stress- 
diagram.  It  will  be  shown  hereafter  that  this  is  true  for  all  kinds  of 
resilience,  both  inside  and  beyond  the  elastic  limit. 

52.  Three  Varieties  of  Resilience. — There  are  three  kinds  of  resilience 
commonly   recognized,    namely,   of   tension    or    compression,  of  bending, 
and  of  torsion.     These,  of  course,  correspond  to  the  three  corresponding 
kinds  of    stresses    and   deformations.      It  will  be  shown  below  that  the 
elastic  resilience  of  a  body,  in  foot-pounds  or  inch-pounds,  is  always  equal 
to  the  product  of  three  factors,  namely : 

(a)  A  numerical  coefficient,  which  is  different  for  each  of  the  three  kinds 
of  resilience,   and  for  different  forms  of  cross-section,  and  for  different 
methods  of  applying  the  external  forces. 

f* 

(b)  The  factor  ~,  or  the  square  of  the  maximum  stress  divided  by  the 

modulus  of  elasticity. 

(c)  The  volume  of  the  body. 

That  is  to  say,  for  any  particular  kind  of  stress  and  form  of  cross- 
section  the  elastic  resilience  varies  directly  as  the  square  of  the  stress- 
intensity  and  as  the  volume  of  the  body,  and  inversely  as  its  modulus  of 
elasticity,  or 

f 
R8  =  lc±==  .  volume (1) 

That  is  to  say,  the  resilience,  or  energy,  which  can  be  absorbed,  or  stored, 
in  a  body  of  a  given  material  and  form,  up  to  a  given  fibre-stress,  is  no 
function  of  the  relative  dimensions  of  the  body,  but  only  of  its  volume. 
In  other  words,  one  cubic  inch  of  steel  will  absorb  and  give  out  the  same 
amount  of  work,  or  energy,  as  the  same  volume  of  fine  wire,  if  the  load  is 
applied  in  the  same  manner,  or  if  the  stress  is  of  the  same  kind,  so  long-as 
the  form  of  cross-section  remains  the  same.* 

53.  Resilience  a  Measure  of  the  Ability  of  a  Body  to  Resist  a  Shock  or 
Blow. — The  magnitude  or  effect  of  a  blow,  or  of  a  falling  body,  is  measured 
by  the  energy  stored  in  the  moving  body  at  the  instant  of  impact.     In  the 
case  of  a  body  which  has  fallen  freely  in  space  under  the  action  of  gravity, 
its  energy  is  Wh,  where  W  is  the  weight  of  the  body  (force  of  gravity),  and 
h  is  the  distance  through  which  the  body  has  fallen  freely  (distance  through 
which  the  force  of  gravity  has  acted).     In  any  case,  the  energy  of  the  body 

Wv* 

is  -— — ,  where  v  is  the  velocity  in  feet  per  second,  and  g  is  the  acceleration. 
y 

*  When  the  stress  is  direct  (tension  or  compression),  the  form  of  cross-section  is 
immaterial.  In  bending  and  torsion,  however,  the  form  of  section  is  important. 


THE  RESILIENCE  OF  MATERIALS. 


77 


of  the  force  of  gravity,  or  32  feet  per  second.  If  a  moving  body,  as  a 
falling  weight,  is  stopped  by  striking  a  fixed  solid  body,  which  is  here 
assumed  to  be  a  test  specimen,  the  energy  of  the  moving  body  is  spent  in 
one  or  all  of  the  following  ways : 

(a)  In  deforming  the  moving  body  itself,  either  within  or  beyond  its 
elastic  limit. 

(b)  In  a  local  deformation  of  both  bodies  at  the  surface  of  contact,  within 
or  beyond  the  elastic  limit. 

(c)  In  moving  the  fixed  body  as  a  whole,  with  an  accelerated  velocity, 
the  resistance  consisting  of  the  inertia  of  the  body. 

(d)  In  moving  the  fixed  body  against  its  external  supports  and  resistances. 

(e)  Finally,  in  deforming  the  fixed  body  as  a  whole  against  the  resisting 
stresses  developed  thereby. 

If  the  moving  body  be  very  hard  and  rigid;  if  the  surfaces  of  contact  are 
comparatively  unyielding;  if  the  specimen  have  a  small  mass  as  compared  to 
the  moving  body,  and  if  it  be  very  rigidly  supported  upon  or  against  a  very 
great  mass  or  weight  which  is  relatively  unyielding;  and,  finally,  if  the  spec- 
imen which  is  to  receive  and  absorb  the  energy  of  the  blow  is  quite  yield- 
ing or  flexible,  and  in  short  if  there  is  nearly  absolute  rigidity  in  all  parts  of 
the  apparatus  except  in  the  body  struck,  and  if  this  yields  only  as  a  whole 
and  not  at  the.  point  of  contact  or  at  its  supports, — then,  and  only  then, 
can  nearly  all  the  energy  of  the  moving  or  falling  body  be  absorbed  by  the 
deflection  or  stretch  or  compression  or  twisting  of  the  specimen.  It  is  prac- 
ticable, by  making  the  energy  of  the  falling  body  consist  mostly  of  weight, 
and  only  to  a  small  degree  of  velocity,  that  is,  by  having  a  heavy  weight  drop 
through  a  short  distance,  to  absorb  up- 
wards of  90$  of  it  in  the  specimen.  It 
goes  without  saying  that  it  is  impossible 
to  get  it  all  stored  in  the  specimen 
under  any  circumstances;  and  if  great 
care  is  not  exercised  in  arranging  the 
test,  but  a  very  small  percentage  may 
be  given  over  to  the  specimen,  the 
rest  being  dissipated  in  the  other  ways 
named  above. 

In  the  stress-diagram  shown  in  Fig. 
51  let  the  vertical  ordlnate  represent 
total  resistance  in  pounds  and  the  hor- 
izontal ordinate  represent  deformation 
of  the  body,  as  a  whole,  measured  at  the 
point  of  contact,  in  inches;  whether  this 
deformation  be  a  bending,  extension, 


compression,  or  twist  is  not  now  material, 
formed    to 


dl  it  is  resisting  this  action  with  a  force  of  p 


When  this  body  has  been  de- 
when  deformed 


78  THE  MATERIALS  OF  CONSTRUCTION. 

to  t/2  it  is  resisting  with  a  force  of  p^ ,  etc.  When  the  deformation  passes 
the  elastic  limit  the  resistance  does  not  increase  as  rapidly  as  the  deformation, 
and  hence  the  diagram  is  no  longer  a  straight  line,  but  becomes  curved. 
A  deformation  of  d3  now  develops  a  resistance  of  pz ,  and  d4  of  p4 ,  etc. 

Now  since  the  work  of  resistance  is  the  sum  of  the  products  of  the  in- 
stantaneous resistances  into  the  corresponding  deformations,  it  is  properly 
represented  by  the  area  of  the  stress  diagram  up  to  the  maximum  deforma- 
tion and  resistance.  That  is  to  say,  the  work  done  on  the  body  to  deflect  or 
deform  it  to  dl  is  indicated  by  the  area  of  oqldl,  the  work  required  to  de- 
form it  to  d9,  and  also  the  energy  stored  in  the  body  when  deformed  to  this 
point,  is  indicated  by  the  area  oq9d^ ,  etc.  So  long  as  the  point  q  falls  on  the 
stress  diagram  inside  the  elastic  limit,  this  amount  of  energy  stored  will  all 
be  given  back  again  by  the  body.  But  when  this  point  q  falls  beyond  the  elas- 
tic limit  point  of  the  diagram,  the  body  is  no  longer  able  to  fully  recover  its 
original  form,  but  it  remains  permanently  deformed.  The  amount  of-  this 
permanent  set  can  always  be  found  by  dropping  lines  qtq9'q4qt'9  etc.,  from  the 
extremity  of  the  diagram  which  marks  the  maximum  load  imposed,  parallel 
to  the  straight  portion  of  the  curve.  These  lines  are  the  return  paths  which  i 
the  specimen  follows  on  the  removal  of  the  deforming  forces  or  loads.  They ! 
are  always  parallel  to  the  elastic  path  of  the  body,  or  to  that  part  of  the 
curve  below  the  elastic  limit.  This  is  true  for  all  kinds  of  stresses  and  dia- 
grams, whether  tension,  compression,  bending,  or  torsion;  and  whether  the 
vertical  ordinate  represents  total  loads  or  resistances,  or  loads  per  square 
inch,  or  intensities  of  stress  on  extreme  fibres. 

In  case  the  specimen  has  had  to  absorb  an  amount  of  energy,  or  work, , 
represented  by  the  area  oq^d^,  therefore,  it  will  give  back  only  so  much  as  is 
represented   by  the    area   q3'q3d3.     The  remainder,  oqaqa',  represents   work 
which  has  been  spent  in  permanently  deforming  the  specimen,  and  which  it 
can  never  give  back,  this  having  been  transformed  into  heat  by  friction. 
Under  our  definition  of  resilience,  therefore,  we  should  have  to  say  that  the 
resilience  of  the  specimen,  for  the  resistance  pa,  is  q3'q3d3,  and  not  the  full 
area  0^3.    This  latter  represents  the  work  done  in  deforming  the  specimen,, 
but  it  cannot  properly  be  called  resilience.    Similarly,  when  the  body  is  dis- 
torted to  dt  with  a  developed  resistance  of  p^  the  resilience  now  is  q^^^,* 
and  oq4qt'  has  been  lost  in  the  permanent  deformation  of  the  specimen,  or 
in  heat. 

The  student  will  readily  perceive  that  the  areas  of  the  triangles  whose 
bases  are  odl}  od^,  q3'd3,  and  q/dt,  respectively,  are  to  each  other  as  the  squares 
of  these  bases,  or  as  the  squares  of  their  altitudes,  pl ,  p^ ,  ps ,  and  pt ,  respec- 
tively, since  they  are  all  similar,  their  sides  being  parallel.  If  their  altitudes 
represented  stresses  per  square  inch,  which  they  might,  then  we  could  say 
the  resilience  of  this  specimen  varied  as  the  square  of  the  stress  developed 
in  it,  as  stated  in  Art.  52,  and  as  will  be  further  shown  analytically,  whether 
this  maximum  stress  be  inside  or  beyond  the  elastic  limit. 


THE  RESILIENCE  OF  MATERIALS. 


79 


Thus  far  in  studying  Fig.  51  we  have  spoken  of  the  "work  of  deforma- 
tion "  without  stating  whether  this  work  was  developed  bv  a  load  slowly  ap- 
plied, or  by  one  quickly  applied,  as 
by  a  falling  weight.  In  fact  it  does 
not  matter  how  this  work  is  done,  a 
given  number  of  foot-pounds  of  en- 
ergy producing  exactly  the  same  ef- 
fect, and  developing  the  same  stress 
diagram,  provided  we  assume  that 
all  the  energy  of  the  quickly  applied 
load  goes  into  the  specimen,  to  pro- 
duce this  particular  deformation. 
This  conclusion  is  also  based  on 
another  assumption,  which  is,  that  the 
relation  betiveen  the  deformation  and  g^ 
its  corresponding  resistance  devel- 
oped in  the  body  is  the  same  for  a  def- 
ormation produced  suddenly  as  for  ^ 
one  produced  by  a  slower  application 
of  external  force.  This  equality  of 
relationship  has  never  been  shown,  as  0 
between  static  and  impact  applica- 


is  Drobable  FlG'  52'~ Showin£  that  a  £reater.  impact 
stress  is  required  to  produce  a  given  de- 


formation. 
344.) 


(Fr.    Com.  Rep.,  vol.   n.  p. 


tions  of  the  load;  but  it 
ithat  this  relation  is  very  nearly  inde- 
pendent of  time,  inside  the  elastic 
limit,  and  with  brittle  bodies  up  to  rupture,  since  it  is  in  this  case  a  molec- 
iular  resistance  to  relative  deformation,  and  not  a  resistance  to t  flow  or  rel- 
iative  displacement.  In  the  case  of  plastic  or  ductile  bodies,  however,  it  has 
jbeen  shown  that  beyond  the  elastic  limit  the  stress  diagrams  developed  by 
impact  and  by  static  loads  are  very  different,  the  former  being  in  the  case 
of  soft  iron  wire  some  30$  greater  in  area.  This  means  that  for  such  mate- 
rials the  actual  energy  absorbed  by  the  specimen  under  impact  is  some  30$ 
more  than  it  is  under  a  static  load.  See  Fig.  52. 

Assuming  now  that  all  the  energy  of  a  blow  is  spent  in  deforming  the 
specimen  in  the  manner  represented  on  the  static  stress-diagram,  we  come 
to  this  very  important  conclusion:  the  energy  of  the  blow,  in  foot-pounds,  is 
equal  to  the  area  of  the  stress-diagram  developed  by  that  blow,  properly  eval- 
uated to  the  scales  of  the  drawing,  when  this  diagram  is  drawn  to  co-ordi- 
nates representing  deformation  and  resistance  thereto.  Thus  if  a  weight 
falls  on  a  body,  as  a  beam,  and  if  we  may  assume  that  very  little  of  the 
energy  spends  itself  otherwise  than  in  bending  the  specimen,  if  .the  speci- 
men deflects  by  the  amount  d^ ,  for  instance,  then  we"  assume  that  the  corre- 
sponding resistance  at  the  instant  of  maximum  deflection  is  p^,  and  that  the 
energy  of  the  blow  was  somewhat  greater  than  the  area  oq //„;  or  by  know- 


80  THE  MATERIALS  OF  CONSTRUCTION. 

ing  the  energy  of  the  falling  body  ( Wli),  and  observing  the  deflection  pro- 
duced, we  could  determine  the  amount  of  energy  absorbed  by  the  specimen 
if  we  only  had  a  stress-diagram  of  this  specimen  under  impact,  as  shoivn  in 
Fig.  52.  Few  such  diagrams  have  ever  been  obtained.  It  has  been  custom- 
ary to  use  for  this  purpose  static  test-diagrams,  carried  beyond  the  elastic 
limit,  and  perhaps  to  failure.  This,  of  course,  destroys  the  specimen  for 
impact  tests;  but  by  having  two  specimens,  presumably  just  alike,  a  static 
test  may  be  made  on  one  of  them,  from  which  a  static  stress-diagram  can  be 
drawn,  and  then  the  impact  test  on  the  other  specimen  can  be  interpreted  by 
this  static  diagram.  Having  done  this,  we  should  still  fail  to  find  the  area 
of  stress-diagram  developed  by  a  single  blow  fully  equal  to  the  energy  of  the 
blow,  because  of  the  dissipation  of  a  portion  of  this  energy  in  other  ways, 
and  also  because  the  impact  stress-diagram  lies  above,  or  outside  of,  the 
static  diagram. 

It  is  common  to  test  materials  by  means  of  falling  weights,  and  often 
the  height  of  drop  is  regularly  increased  until  failure  occurs.  Let  us  follow 
the  course  of  such  a  test,  referring  again  to  Fig.  51.  Thus  we  will  suppose 
all  the  energy  of  the  blow  goes  into  the  specimen  (or  it  would  serve  as  well 
to  suppose  a  certain  fixed  percentage  is  absorbed  by  the  specimen),  and  that 
the  first  blow  deformed  the  specimen  to  dl ,  the  second  to  d^ ,  the  third  to  6?8i 
and  the  fourth  to  dt.  Now  what  were  the  energies  of  these  blows,  if  all 
went  into  the  specimen  each  time  ?  Evidently  the  energy  of  the  first  blow 
was  that  indicated  by  the  area  oq^l^  of  the  second  by  oq^d^  of  the  third 
by  oq^d^  and  of  the  fourth  by  q^q^q^d^.  Thus  we  see  that  all  the  first  area; 
is  included  in  the  second,  all  of  both  first  and  second  in  the  third,  and  i 
large  part  of  the  third  (qs'qzds)  in  the  fourth.  These  areas  are  therefore 
not  mutually  exclusive,  so  that  the  sum  of  the  energies  of  all  the  blow* 
(2W7i)  is  not  equal  to  the  total  area  of  the  stress-diagram  developed  b} 
them,  oq4dt.  Neither  is  the  energy  of  the  last  blow  equal  to  this  area,  and 
in  fact  there  is  no  relation  between  the  total  area  of  the  stress-diagrams 
oq4d4,  and  the  energy  of  one  or  all  of  the  blows  given.  If  we  now  add  to 
this  statement  the  evident  fact  that  we  can  never  know  in  practice  whai 
portion  of  the  energy  of  any  blow  is  spent  in  deforming  the  specimen  (ano 
often  we  cannot  tell  what  this  proportion  is  within  over  50$,  and  sometime)1 
it  has  been  assumed  that  it  all  went  into  the  specimen  when  there  could  no- 
have  been  more  than  five  per  cent  of  it  so  spent  !),  it  becomes  patent  thai 

NO    ABSOLUTE   CONCLUSION   WHATEVER   CAN    BE   BASED    ON   IMPACT   TESTS 

Some  relative  conclusions  may  be  drawn  by  subjecting  two  or  more  liki 
specimens  to  exactly  identical  treatment  and  finding  which  withstands  thlj 
greater  number  of  blows.  Even  then  the  apparent  relative  strength  depend' 
largely  on  wliat  particular  magnitude  of  blow  be  selected  for  making  tests 
Also  a  very  small  difference  (apparently)  in  the  character  of  the  foundawH 
on  which  the  specimen  rests  may  make  a  very  great  difference  in  the  per 
centage  of  the  total  energy  which  goes  into  the  specimen.  Hence  suc!> 


THE  RESILIENCE  OF  MATERIALS.  81 

omparative  tests  should  always  be  made  on  the  same  foundation,  and  all 
he  elements  of  the  test  exactly  duplicated.* 

In  order  to  obtain  the  absolute  characteristics  of  any  material,  a  com- 
dete  stress-diagram  should  be  obtained  by  static  tests.  The  area  of  such  a 
iagram  up  to  its  elastic  limit  indicates  the  total  energy  of  the  single  shock 
r  blow  it  could  withstand  up  to  that  limit,  or  without  taking  a  permanent 
et  (provided  this  energy  all  went  into  the  specimen),  and  the  area  of  this- 
.iagram,  up  to  rupture,  indicates  the  total  energy  of  the  single  blow  it 
ould  absorb  without  actually  breaking. 

It  must  also  be  observed  that  in  addition  to  the  impact  stress  being 
•reater  for  given  deformations,  beyond  the  elastic  limit  with  ductile  mate- 
ials,  the  total  elongation  at  rupture  is  also  much  greater  when  produced  by 
sudden  blow  than  when  produced  in  a  static  test,  and  hehce  the  area  of 
tie  stress  diagram  thus  developed  may  be  very  much  larger  than  the  static- 
jest  diagram  on  the  same  material. 

For  an  absolute  measure  of  a  given  material  to  withstand  a  shock  or 
low,  therefore,  it  is  necessary  to  give  it  a  static  test  in  some  kind  of  a  test- 
bg-machine,  whether  this  test  be  in  tension,  or  in  compression,  or  in  cross- 
lending,  or  in  torsion.  Then  the  area  of  the  stress-diagram  up  to  the  elastic 
imit,  divided  by  the  volume  of  the  specimen  under  test,  is  a.  measure  of  the 
bility  of  the  material,  per  unit  of  volume,  to  absorb  and  give  out  energy ', 
r  to  resist  repeated  shocks  without  injury  ;  and  the  total  area  of  the  stress- 
liagram  is  its  measure  to  resist  a  single  blow  without  rupture.\ 

It  is  necessary  in  this  connection  to  guard,  the  student  against  several 
iaisconceptions. 

(a)  By  a  "  slow  "  or  "  static  "  test  is  meant  such  a  gradual  imposition  of 
he  load  as  will  give   to    the  moving  parts  an  inappreciable  velocity,  or 
nomentum,  or  vis  viva.     Evidently  any  ordinary  test  in  a  testing-machine 
ulfils  this  condition. 

(b)  By  an  impact  test,  or  a  shock,  or  a  blow,  is  meant  a  genuine  striking 
>r  impact,  in  which  the  force  of  the  blow  is  nearly  all  due  to  the  speed  or 
velocity  of  the  moving  body  or  falling  weight,  and  only  slightly  due  to  its 
static  weight  alone. 

(c)  Aside  from  the   two  methods  which   alone  have   been   under  dis- 
cussion in  this  article,  there  is  another  method  of  loading,  called  a  "  sudden 
imposition  of   load."     Thus  in  the  case  of  placing  a  load  on  a  beam,  if 
the   load    be   brought   into   contact   with   the    beam,  but   its  weight   sus- 
tained by  external  means,  as  by  a  cord,  and  then  this  external  support  be 

*lt  is  not  uncommon  to  find  impact  tests  described  by  giving  only  the  weight  of 
hammer  and  height  of  fall,  with  no  description  of  the  character  of  the  supports.  It 
has  also  been  customary  to  rest  stamp-mills  on  spring-timbers  to  lessen  the  force  of  the 
blow  ! 

f  Except  that  for  ductile  materials,  in  which  the  impact  stress-diagram  is  greater 
than  the  static  stress-diagram,  as  shown  in  Fig.  52. 


82  THE  MATERIALS  OF  CONSTRUCTION. 

suddenly  (instantaneously)  removed,  as  by  quickly  cutting  the  cord,  thei 
although  the  load  is  already  touching  the  beam  (and  hence  there  is  no  re; 
impact),  yet  the  beam  is  at  first  offering  no  resistance,  as  it  has  as  y< 
suffered  no  deformation.  Furthermore,  as  the  beam  deflects  the  resistam 
increases,  but  does  not  come  to  be  equal  to  the  load  until  it  has  attained  ii 
normal  deflection.  In  the  meantime  there  has  been  an  unbalanced  force  ( 
gravity  acting,  of  a  constantly  diminishing  amount,  equal  at  first  to  th 
entire  load,  but  now  reduced  to  zero  when  the  resistance  has  come  to  t 
equal  to  the  load,  at  the  normal  deflection.  But  at  this  instant  both  th 
load  and  the  beam  are  in  motion,  the  hitherto  unbalanced  force  having  pn 
duced  an  accelerated  velocity,  and  this  velocity  of  the  weight  and  beai 
gives  to  them  an  energy,  or  vis  viva,  which  must  now  spend  itself  in  ove: 
coming  an  excess  of  resistance  over  and  above  the  imposed  load,  and  th 
whole  mass  will  not  stop  until  the  deflection  (as  well  as  the  resistance)  he 
come  to  be  equal  to  twice  that  corresponding  to  the  static  load  imposet 
Hence  we  say  the  effect  of  a  suddenly  imposed  load  is  to  produce  twice  th 
deflection  and  stress  of  the  same  load  statically  placed.  It  must  be  eviden- 
however,  that  this  case  has  nothing  in  common  with  either  the  ordinal) 
"  static"  tests  of  structural  materials  in  testing-machines,  or  with  impac 
tests.  It  is  introduced  here  to  prevent  a  confusion  of  mind  in  these  mattei 
•often  found  to  exist  with  persons  whose  conceptions  of  such  problems  i 
mechanics  are  not  clear. 

54.  Resilience  Areas  in  Stress-diagrams. — It  was  shown  in  the  previoo 
article,  in  discussing  Fig.  51,  that  the  shaded  triangular  areas  represents 
the  resilience  of  the  specimen  for  the  several  loads  imposed.  It  will  now  fc 
shown  that  these  areas  may  be  represented  as  one  figure  with  continuousl' 
added  increments. 

Referring  again  to  Fig.  51,  if  the  permanent  set,  oqs,  be  laid  off  on  p^ 
from  p3  giving  q9",  oqt  on  p4qt  from  p4  giving  <//',  etc.,  and  drawing  a  curr 
through  these  points  from  ^3,the  elastic-limit  stress,  the  curve  so  draw* 
may  be  called  the  curve  of  permanent  sets.  If  we  now  regard  the  spao 
intercepted  between  this  and  the  stress-diagram,  it  is  evident  that  the  lengt 
of  the  horizontal  intercept  increases  directly  as  its  altitude  above  the  hon 
zontal  axis,  since  these  intercepts  are  the  bases  of  the  similar  triangles  o« 
the  horizontal  axis,  whose  apexes  lie  in  those  horizontal  lines.  This  curve- 
area  op^q^'q".  .  .  qtqsq,,o  is  therefore  a  more  general  type  of  a  true  triangle 
whose  area  is  simply  equal  to  its  upper  base  (the  horizontal  intercept  whic 
equals  the  elastic  deformation)  into  one  half  its  altitude  (which  is  the  max? 
mum  stress  produced,  or  load  imposed).  In  other  words,  the  followin 
triangles  are  equal,  because  they  have  equal  altitudes  and  bases.  Sine 
they  also  have  equal  angles  at  the  vertex,  they  are,  in  a  more  general  sense 
similar  triangles : 

Triangle  oq^d^     =  triangle  op^q^ 
Triangle  qt'qtdt  =  triangle  optqt"qtqj; 


THE  RESILIENCE  OF  MATERIALS.  83 

Triangle  q/q.d.  =  triangle  op9q,"qS'q<q,q,o. 

etc.  etc. 

Hence  by  simply  constructing  both  the  stress-deformation  and  the 
•,ress-set  curves,  we  may  indicate  directly  the  resilience  or  work  which  the 
pecimen  will  be  able  to  give  back  after  having  been  stressed  to  any 
3signed  limit.*  The  value  of  this  resilience  is  always  one  half  the  product 
f  the  final  stress  into  the  difference  between  the  final  distortion  and  the 
ermanent  set;  or,  in  general,  whether  inside  or  beyond  the  elastic  limit,  the 
vsilience  is  equal  to  one  half  the  product  of  the  final  load  or  stress  into  the 
'astic  deformation.\ 

55.  Resilience   of  Bodies  under  Direct  Stress. — When  a  body  of  a  uni- 
>rm  cross-section  and  of  a  definite  length  is  subjected  to  the  action  of 
xternal  forces,  producing  direct  tension  or  compression,  the  deformation 

rod  need  in  the  body,  from   eq.   (2),  Chapter  I,  is    a  =  '-^.     If  A  =  the 

lit 

ross-section  of  the  body,  then  the  total  external  force  applied  is  P  =.  pA. 
he  total  external  work  is  then 

Pa  _pA   pi  _  1  p* 

T   '~2'^~2WAl (3> 

But  since  this  is  equal  to  the  internal  work  of  resistance,  and  since 
I  —  volume  of  the  specimen,  we  have 

1    ff 

Rd  —  resilience  in  direct  stress  —  —  .-^  .  volume;  ...     (3) 

&    -& 

r  per  unit  of  volume, 

*=*f <*> 

Since  p  and  E  are  given  in  pounds  per  square  inch,  the  volume  must 
so  be  in  cubic  inches. 

If  p  is  made  equal  to  the  elastic  limit  of  the  material,  the  corresponding 
alue  of  rd  is  the  primitive  elastic  resilience  in  inch-pounds  per  cubic  inch. 
eyond  the  elastic  limit,  the  elastic  resilience  is  indicated  by  the  triangles 
Va^s*  y/Vtd*!  etc.,  in  Fig.  51,  corresponding  in  each  case  to  the  new  or 
irtificially-raised  elastic  limits pa,  pt,  etc.     These  subsequent  elastic  resili- 
ence values  may  be  called  the  artificially-raised  elastic  resilience. 

As  defined  in  the  previous  article,  all  resilience  is  elastic  resilience,  but 
:he  term  "elastic"  is  retained  here  in  order  to  insure  that  it  is  not  confused 
vvith  the  term  "total  resilience,"  which  is  sometimes  misused  and  made  to 
nean  the  total  area  of  the  stress-diagram,  which  the  author  of  this  work 
vvill  not  admit  is  resilience  in  any  sense. 

56.  Resilience  in  Cross-bending. — The  deflections  of  beams  loaded  and 
supported  in  different  ways,  in  terms  of  the  stress  on  the  extreme  fibre,  are 

*  When  the  stress  passes  a  maximum  and  both  these  curves  begin  to  descend,  the 
included  area  here  becomes  negative. 

f  True  under  the  author's  definition  of  resilience,  but  not  true  when  this  term  is 
made  to  mean  the  work  or  energy  absorbed  instead  of  the  energy  given  back. 


THE  MATERIALS  OF  CONSTRUCTION. 


given   in   column   four   of  the  table  on   pages  62-65.     For  any  case   the 

/72 
deflection  may  be  represented  by  the  term  k  '~r9  where  k  is  a  numerical 

coefficient  which  varies  for  the  different  cases,  but  the  values  of  which  are 
given  in  that  table.  Since  the  resilience  of  a  beam  when  developed  by 
falling  weights,  or  other  impact  loads,  would  produce  deflections  corre- 
sponding to  concentrated  loads,  only  concentrated-load  deflections  as  given 
in  the  table  need  be  here  considered.  Thus,  for  a  beam  supported  at  the^ 
ends  and  loaded  at  the  centre,  the  deflection,  in  terms  of  the  stress  on  the  1 

outer  fibre,  is  A  =  -  ~r.     But  the  load  which  will  produce  the  stress  /"on 

0   Jjjil 

the  outer  fibre  is  (see  column  five  of  table)  P  =  —-.     The  external  work; 

done  on  the  beam  in  deflecting  it,  which  must  equal  the  internal  work  of ! 
resistance,  or  the  resilience,  if  /  is  inside  the  elastic  limit,  is 


«  -r  i 

Resilience  =  —  =  -.-.1 


For  a  solid  rectangular  cross-section,  /  = 
Substituting  this  in  eq.  (5),  we  have 

Resilience  of  a  solid  rectangular  beam  loaded  at  the  centre  and 
supported  at  the  ends  = 


1      /"2  1     /'2 

— .  ^  .  bhl  =  — .  --JT  .  volume. 

lo     Hi  lo    HJ 


(6) 


If  the  bending  moment  had  been  uniform  throughout  its  length,  as  i& 
the  case  with  a  spiral  or  helical  spring  when  under  a  bending  stress,  the 
movement  of  one  end  of  the  spring  should  be  determined,  and  this  multi- 
plied by  one  half  the  final  force  applied  at  this  point.  But  since  the 
internal  work  of  resistance  is  always  equal  to  the  external  work  of  deforma-i 
tion,  we  may  measure  up  the  internal  work  and  call  this  the  resiliences 
The  case  of  a  beam  (or  a  spring)  under  a  uniform  bending  moment  is  a 
favorable  case  for  this  purpose.  Thus -assume  a  spiral  or  helical  spring 
made  of  a  steel  bar  having  a  rectangular  cross-section  whose  original- 
dimensions  were  I,  b,  and  h.  When  coiled  into  a  spring  (the  dimensions  oi 

the  coil  being  immaterial  for  our  purpose) 
and  a  couple  producing  bending  moment 
applied  to  it,  thus  developing  in  the  spring 
throughout  its  entire  length  a  moment  oi> 
resistance  which  we  will  suppose  is  such  as 
to  give  rise  to  the  elastic-limit  stress  /  on 
the  outer  fibres  throughout  the  entire  length 
of  the  coiled  bar,  we  are  to  measure  up  the 
total  internal  work  of  resistance,  or  th( 
energy  thus  stored  in  the  spring.  Since  the  fibre-stress  is  uniformly  vary- 


FIG.  53. 


THE  RESILIENCE  OF  MATERIALS.  85 

ag  across  the  section  of  the  bar,  and  is /on  the  outer  fibres  on  each  side, 
3  is  evident  that 

il       2f 

The  stress  on  any  fibre  =  p  =  ay  =  f  —  —  ~-y9     .     .     .     (7) 

y  i 

'here  y  =  distance  of  fibre  from  neutral  axis,  and 

y^  =  distance  of  outer  fibre  from  neutral  axis  =  — ; 
f  =  stress  per  square  inch  on  outer  fibre. 
But 

The  stretch  of  any  fibre  =  a  =  -~r  =  -by*    ....    (8) 

here  p  =  stress  per  square  inch; 

/  —  length  of  bar  of  which  spring  is  composed; 
E  =  modulus  of  elasticity. 

Therefore 

2^2     ^ 

The  ivork  of  resistance  of  any  fibre  =  -—  .  -=-,  .  y*.     .     .     (9) 

J^J  fir 

The  work  of  resistance  of  any  zone  of  fibres  bdy  in  area  of  cross-section, 
istant  y  from  the  neutral  axis,  would  be  —-  .  ^  .  y*dy,  and 


r+Y 

he  total  work  of  resistance  =  resilience  =  R  =     I        §L.  _  . 

J    h    E      li 


y*dy 


_»/'  .  N.  *!  -  L.f-  m 
i~^   y  13-6  ^ 

~  2  ~   2 

1     /"' 
=  —  •  -p.  volume  of  spring  ...     ..........  .    .     (10) 

Comparing  this  with  eq.  (5)  we  see  that  fifty  per  cent  more  energy  can 
e  absorbed  by  a  beam  or  spring  when  subjected  to  a  uniform  bending 
tioment  than  when  the  moment  increases  uniformly  from  the  ends  to  the 
entre,  or  from  one  end  to  the  other, 

57.  Resilience  in  Torsion.  —  Referring  to  Fig.  23  we  see  that  the  external 

pork  is  —  —  ,  where  0  is  the  distortion  angle  and  a  —  length  of  arm  of  the 

ouple,  whose  forces  are  P.    But  from  eq.  (14),  Chapter  III,  when  the 
aoment  Pa  is  on  the  specimen  the  stress  on  the  outer  fibre  is 


=  -&•     or 

Uso,  from  eq.  (15), 

„       2Pal 


86 


THE  MATERIALS  OF  CONSTRUCTION. 


Pa6 
-rr,we 


Substituting  here  the  value  of  Pa  above,  we  have 

%nr*E  ~  2  r£J 

Combining  this  with  the  value  of  Pa  again  to  get  the  value  of 
have 

~P 'n  f)  £\        f  2 

Work  of  torsion  on  solid  cylinder  — =  -.•%-.  7tr*l 

2          8     E 

=  IT    E'  volume-   •     •     • 

58.  Comparative  Resilience  of  Bodies  under  Different  Kind  of  Stress. — 
For  bodies  of  uniform  cross-section  we  have  the  following  table  of  values  of 
resilience  in  inch-pounds  per  cubic  inch,  and  their  relative  capacities  to  ab- 
sorb and  give  out  energy,  taking  the  capacity  in  direct  stress  as  unity. 

COMPARATIVE   RESILIENCE   OF   BODIES. 


Figure. 

Kinds  of  Stress. 

Resilience  in  inch- 
pounds  per  cubic 
inch.     =  r. 

Relative  Capacity 
for  Absorbing  and 
Giving  out  Energy. 

22 

'///M                    L 

T         W///////, 

Direct  tension  or  compression. 

H'W 

1 

\f 

Cross-bending  with  bending 
moment  uniformly  increas- 
ing longitudinally. 

1  /* 

US'  E 

i 

9 

'x 

I 

HSi  !  i  U^ 

^VJ       1       iS^ 

1 

jjjjii^            \ 

• 

Cross  -bending  with  bending 
moment  uniform  longitudi- 
nally. 

i    r 

6    '   E 

1 
3 

f 

C 
( 

v    Ei'iiljii!  !ii!!/t 

izfomnA) 

py 

i 

1     < 

Torsion. 

5    /2 

5 

_       _ 

8  '  E 

EXAMPLES  ON  PART  I.  86a 


EXAMPLES    ON    PART    I. 

1.  A  section  of  a  steel  bar  1  in.  in  diameter  and  8  in.  long  elongates  0.01  in.  for 
an  increase  in  tensile  stress  of  30,000  Ibs.     What  is  the  modulus  of  elasticity  ? 

2.  What  reduction  in  temperature  would  bring  a  wrought-iron  bar,  immovably 
fixed  at  its  ends,  to  its  elastic  limit  of  26,000  Ibs.  tensile  stress  per  square  inch? 
Take  E  =  28,000,000  and  the  coefficient  of  expansion  =  0.0000065  per  degree  F. 

Am.  142°.  8 

3.  Find  the  proportionate  change  in  volume  of  a  brass  cube  which  is  subjected  to 
a  compress! ve  stress  in  one  direction  of  10,000  Ibs.  per  square  inch.     Take  E  — 
15,000,000.     What  is  its  change  in  volume  for  a  fluid  pressure  of  this  amount  in  all 
directions?  Ans.  0.00023- ;  0.00069. 

4.  What  is  the  shearing  modulus  of  elasticity  for  steel  if  #  =  29,000,000  and 
Poisson's  ratio  =  0.27  ?  Ans.  E8  =  0.39^. 

5.  Find  the  modulus  of  elasticity  of  steel  from  Fig.  6,  making  allowance  for  the 
locus  cutting  the  vertical  axis  at  1000  pounds  above  the  origin.     Use  the  deformation 
of  0.001  and  its  corresponding  stress-increment  in  pounds  per  square  inch.     From 
the  same  diagram  find  the  elastic  limit,  the  ultimate  strength,  and  the  percentage 
of  elongation. 

6.  The  following  is  a  record  of  a  test  on  cast  iron  : 

Loads  per  square  inch 

in  pounds 1000  5000  10000  15000  20000  25000  30000  31040 

Proportionate  deforma- 
tions   0  .00022.00055  .00097  .00150  .00220  .00368  broke 

Plot  this  record  and  determine  from  it:  (1)  The  modulus  of  elasticity;  (2)  The  ap- 
parent elastic  limit ;  (3)  The  total  percentage  of  elongation  (by  extending  the  plotted 
curve  till  the  breaking  load  is  reached);  (4)  The  work  required  to  break  the  speci- 
men in  foot-pounds  per  cubic  inch  of  metal  (obtained  by  finding  the  area  of  the 
diagram  and  evaluating  it  to  the  scales  of  the  drawing,  see  Art.  53). 

7.  Assume  a  brick  to  be  8  in.  long,  4  in.  wide,  and  2  in.  thick.     From  equation 
(12),  p.  31,  find  the  relative  crushing  strength  of  the  brick  per  unit  area  when 

i  tested  flatwise,  edgewise,  and  endwise,  taking  the  strength  of  a  cubical  specimen  of 
!  the  same  material  as  unity.  Ans.  1.22;  0.89;  and  0.83. 

8.  A  stone  cube  two  inches  on  a  side  has  its  edges  chamfered  or  rounded  so  that 
the  bearing  surfaces  are  but  1.8  in.  square.     What  is  its  total  crushing  strength  as 
compared  to  the  strength  of  a  full  cube  ?    What  is  its  strength  per  square  inch  of 
bearing-surface  as  compared  to  the  strength  per  square  inch  of  a  full  cube  ?     (See 
Fig.  18.)  Ans.  85  per  cent;  103  per  cent. 

9.  By  how  much  is  a  centrally  loaded  column  12  in.  square  weakened  by  adding 
four  inches  of  the  same  material  to  one  side  of  the  column  without  shifting  the  load  ? 

Ans.  The  maximum  stress  in  the  column  is  increased  by  31£  per  cent. 

10.  A  steel  rod  1/4  in.  in  diameter  and  30  in.  long  is  used  as  a  torsional  spring  for 
closing  a  door.     What  will  be  the  increase  in  the  moment  of  torsion  from  giving 
the  rod  an  additional  twist  through  90°,  the  shearing  modulus  of  elasticity  being 
taken  as  12,000,000  ?    What  will  be  the  maximum  increased  shearing  stress  in  the 
rod  due  to  this  angular  movement  ?    What  will  be  the  increase  in  the  force  required 
to  hold  the  door  in  this  position,  the  door-knob  being  30  inches  from  the  hinges? 

Ans.  244  inch- pounds;  78,500  Ibs.  per  square  inch  ;  8  pounds. 

11.  A  wooden  beam  8  in.  by  16  in.  in  cross-section  and  20  ft.  long  carries  a 
uniform  load  of  1000  Ibs.  per  running  foot.     Find  the  maximum  direct  stress  on  the 
outer  fibres  and  the  maximum  shearing  stress  in  the  beam. 

A         j  1170  Ibs.  per  square  inch  direct  stress; 
Ans.    |    11?   k4     tl        tl        M     shearingu 

12.  For  the  same  beam  and  load  as  in  Ex.  11,  find  the  deflection  of  the  beam, 
taking  E  =  1,200,000.     If  the  deflection  were  observed  to  be  3/4  in.,  what  would  be 
the  modulus  of  elasticity?  Ans.  1.1  in  deflection;  1,760,000  modulus. 

13.  A  flitched  beam  is  composed  of  two  sticks  4  in.  by  16  in.  by  16  ft.  long-,  and 
a  steel  plate  3/4  in.  by  16  in.  of  the  same  length,  and  carries  a  load  of  2000  pounds 


866  THE  MATERIALS  OF  CONSTRUCTION. 

per  running  foot.  Find  the  portion  of  the  load  carried  by  each  part,  the  maximum 
fibre-stresses  resulting,  and  the  deflection  at  the  centre,  taking  E  =  80,000,000  for 
the  steel  and  1.500,000  for  the  timber 

A          S  Steel:    1305  Ibs.  per  foot;  15,660  Ibs.  ;  0.25  inch. 
\  Timber:  695  "      "      "  782    "          "      " 

14.  How  many  foot-pounds  of  energy  per  pound  of  steel  can  be  stored  in  a  steel 
helical  or  spiral  spring  coiled  about  an  axle,  by  winding  it  up  until  the  stress  in 
the  outer  fibre  is  80,000  Ibs.  per  square  inch,  E  being  taken  equal  to  30,000,000  ? 

Am.  17.8. 

15.  How  much  would  such  a  spring  weigh  which  could  absorb  the  energy  of  a 
street-car  weighing  20,000  Ibs.,  and  moving  at  the  rate  of  six  miles  per  hour  on  a 
down  grade  just  sufficient  to  overcome  the  frictional  resistances  ?    Would  the  size  of 
the  cross-section  of  such  a  spring  affect  its  necessary  weight  ? 

Could  such  a  spring  be  designed  so  as  to  reach  this  fibre-stress  when  the  car  had 
stopped,  and  also  so  as  to  be  exerting  the  maximum  torsional  moment  on  the  car- 
axle  without  causing  the  wheels  to  slip  ?  Is  such  a  device  practicable  ?  * 

Am.  2315  Ibs. 

16.  To  what  extent  can  energy  be  stored  in  metallic  springs  of  any  sort  ?    Could 
they  ever  be  used  for  the  storing  of  motive  power  ?     (This  has  often  been  attempted.) 

17.  A  pendulum,  mounted  on  knife-edges,  weighs  50  Ibs.,  and  its  centre  of  gravity 
is  8  feet  from  the  pivot-supports.     It  is  moved  to  an  angle  of  30°  from  the  vertical, 
and  is  allowed  to  swing  and  strike  the  centre  of  a  cast-iron  bar  1  in.  square,  resting 
on  absolutely  rigid  supports  (or  assumed  to  be  such)  2  feet  apart.     The  pendulum  in 
falling  breaks  the  bar  and  moves  a  horizontal  distance  of  24  in.  beyond  its  true  ver- 
tical position  before  it  comes  to  a  stop.     What  is  the  shock- resisting  capacity  of  the 
iron  in  inch- pounds  per  cubic  inch  of  metal  in  cross-breaking  under  a  concentrated 
load?  Ans.ZOA. 

18.  Assuming  the  stress-diagram  of  a  static  test  of  such  a  bar  in  cross-bending  to 
be  a  triangle,  what  would  its  final  deflection  be  if  the  breaking  load  were  such  as  to 
correspond  to  a  modulus  of  rupture  of  40,000  Ibs.  per  square  inch  ? 

Ans.  0.88  inch. 

*  This  is  a  favorite  device  with  "  car-starter"  inventors.  See  an  article  by  the  Author  in  Jour.  Assc, 
Eng.  Socs.,  vol.  iv.  p.  393. 


PART  II. 

MANUFACTURE   AND     GENERAL    PROPERTIES    OF    THE 
MATERIALS   OF  CONSTRUCTION. 


CHAPTER  VII. 
CAST  IRON. 

GENERAL  CLASSIFICATION  OF  IKON  AND  STEEL. 

59.  Importance  of  the  Subject. — While  the  use  of  iron  in  a  small  way, 
for  offensive  and  defensive  weapons  of  war  and  for  utensils,  is  doubtless 
older  than  authentic  history,*  it  is  only  since  its  manufacture  has  become 
possible  on  a  grand  scale,  by  the  aid  of  steam-power,  that  it  has  become  a 
common  material  of  engineering  and  architectural  construction.  It  has 
now  nearly  replaced  the  use  of  timber  in  engineering  works,  and  it  is  rapidly 
replacing  the  use  of  wood,  stone,  and  brick  in  architeccural  designing.  So 
dependent  now  are  all  kinds  of  construction  on  the  use  of  iron,  that  the 
condition  of  the  iron-manufacturing  industry  is  universally  regarded  as  a 
true  index  of  the  general  state  of  trade  and  commerce  the  world  over.  Since 
iron,  therefore,  in  its  various  states,  is  more  used  in  engineering  construc- 
tion than  all  other  kinds  of  materials  combined,  a  corresponding  amount  of 
space  is  given  to  a  study  of  it  in  this  work.f 

*  There  is  now  in  the  British  Museum  («)  a  sickle-blade  found  by  Belzoni  under  the 
base  of  a  sphinx  near  Thebes;  (&)  a  blade  found  by  Col.  Vyse  embedded  in  the  mortar  of 
one  of  the  Pyramids  ;  (c)  a  portion  of  a  cross-cut  saw  exhumed  by  Layajd  at  Nimroud. 
These  may  be  of  meteoric  origin.  The  reason  more  specimens  of  iron  and  steel  are  not 
found  may  be  due,  however,  to  their  rapid  oxidation  when  exposed  to  air  and  moisture. 
The  stone  and  bronze  implements  have  resisted  this  action,  and  hence  many  have  assumed 
that  in  the  "stone  "  and  "  bronze  "  ages  no  iron  was  in  use. 

f  A  chronological  review  of  the  greatest  discoveries  and  inventions  in  iron  manufac- 
ture is  here  given  : 

4000  B  c.  to  |  Wrought  iron  by  the  direct  process  from  the  ore  in  small  quantities 
about  1500  A. D.  )  by  means  of  charcoal,  and  this  made  into  cement- or  blister-steel. 
About  1500  A.D. — Cast  iron  made  in  Germany  with  charcoal. 

1620-1735.         Cast-iron  made  by  Dud  Dudley  in  England  with  coke,  but  the  prac- 

87 


88  TEE  MATERIALS  OF  CONSTRUCTION. 

60.  Classifications  of  Iron  and  Steel. — Iron  and  steel  may  be  classified 
according  to  its  qualities,  structure,  and  composition,  or  according  to  its 
methods  of  manufacture.  Apparently  the  former  is  the  more  significant 
basis  of  classification,  but  in  English-  and  French-speaking  countries  the 
latter  basis  has  come  to  be  universally  adopted.  We  will,  however,  here  first 
classify  these  products  according  to  their  more  significant  qualities  (the 
method  used  in  Germany). 

IRON  AND  STEEL  CLASSIFIED  ACCORDING  TO  QUALITIES. 
Malleable. 

Cast,  when  molten,  into  a  malleable  mass  or  ingot. 
Ingot  Iron — cannot  be  hardened  by  sudden  cooling. 
Ingot  Steel — can  be  hardened  by  sudden  cooling. 
Aggregated    from    pasty   particles    without    subsequent    fusion 
(puddling  process). 

tice  lapsed  till  revived  in  1735  by  Abraham  Darby.  Blast  from  leather 
bellows  driven  by  water-power. 

1740.  Cement-steel  melted  in  crucibles  by  Huntsman  near  Sheffield,  England. 

1760.  The  steam-engine  of  Watt  applied  to  produce  the  blast  for  making  pig- 

iron,  and  to  drive  rolls  and  hammers  in  working  the  wrought  iron 
and  steel. 

1783-4.  Grooved  rolls    of  various  forms,  driven   by  the    steam-engine,  and 

wrought  iron  made  from  pig  iron  by  "dry-puddling,"  both  by 
Cort,  England.  White  iron  used  in  the  "dry"  process.  These 
inventions  lie  at  the  base  of  the  supremacy  of  Great  Britain  in  the 
iron  trades. 

1829.  Hot  blast,  used  in  blast-furnaces  in  Scotland  by  Neilson,  thus  greatly 

cheapening  the  cost  of  production. 

1830.  The  "wet-puddling"  process  of  making  wrought-iron,  or  "pig-boil- 

ing," introduced  by  J.  Hall,  England. 

1840.  Use  of  manganese  in  making  crucible  cast  steel,  introduced  at  Sheffield 

by  /.  M.  Heath,  which  reduced  the  cost  of  steel  by  50  per  cent. 

1856.  The  Bessemer  process  of  making  steel,  patented  by  Sir  Henry  Bessemer 

in  England  (son  of  a  French  refugee,  born  1813),  this  "  being  of  far 
more  importance  to  the  world  than  all  the  gold  of  California  and 
Australia." 

1861.  Invention  of  the  regenerative  gas  furnace  by  Sir  W.  Siemens  in  Eng- 

land (born  in  Hanover,  1823),  and  educated  at  the  Magdeburg  Poly- 
technicum  and  at  Gottingen). 

1863.  Application  of  the  Siemens  furnace  to  the  open-hearth  process  of  mak- 

ing steel  by  P.  and  E.  Martin  in  France,  thus  originating  the  Sie- 
mens-Martin process  of  steel-making  now  employed  for  nearly  all  the 
soft  and  mild  steel  used  in  structural  work,  and  for  steel  castings. 

1878.  The  invention  of  the  basic  process  of  making  steel,  by  which  the  phos- 

phorus of  the  ore  is  eliminated,  by  8.  G.  Thomas  and  P.  C.  Gilchrist 
(cousins)  in  England.  (First  public  demonstration  April  4,  1879.) 
By  this  process  the  range  of  ores  which  can  be  used  for  steel-making- 
is  enormously  increased,  especially  in  Europe,  while  it  is  used  often. 
in  America. 


CAST  IRON.  89 

Weld  Iron — cannot  be  hardened  by  sudden  cooling. 
Weld  Steel — can  be  hardened  by  sudden  cooling. 
Semi-malleable. 

Steel  Castings — malleable  metal  cast  into  final  forms. 

Malleable  Cast  Iron — non-malleable  metal   (cast  iron)   cast  into 

final  forms  and  then  brought  to  a  semi-malleable  condition. 
Non-malleable. 
Cast  Iron. 
Hard  Cast  Steel. 

The  significant  criterion  here  employed  to  distinguish  between  iron  and 
steel  consists  in  the  hardening  effects  of  sudden  cooling  from  a  bright-red 
heat.  This  is  not  a  very  satisfactory  criterion,  however,  since  all  such 
metal  is  hardened  somewhat  by  sudden  cooling. 

What  are  commonly  known  as  wrought  iron  and  steel,  however,  are 
made  by  radically  different  processes — one  being  the  formation  of  the 
product  in  a  melted,  or  liquid,  state  and  then  casting  it  into  a  mould, 
forming  what  is  called  an  ingot;  the  other  consisting  in  forming  the 
product  in  a  pasty  or  spongy  state  in  a  bath  of  melted  or  liquid  foreign 
matter,  from  which  it  is  lifted  and  immediately  forged  or  rolled.  When 
formed  in  the  melted  state  it  is  purified  from  all  foreign  matter  except 
such  as  enters  into  its  own  composition,  while  when  formed  in  the  pasty 
or  spongy  state,  in  a  bath  of  melted  foreign  matter,  a  considerable 
proportion  of  this  foreign  matter  or  slag  is,  of  necessity,  lifted  out  with 
the  pasty  aggregation,  called  a  "  puddle-ball,"  and  some  of  this  slag 
remains  distributed  through  the  iron  even  after  it  is  rolled,  thus  giving 
it  a  kind  of  fibre  or  grain.  While,  therefore,  the  mechanical  qualities  of 
the  puddled  product  may  be  almost  identical  with  those  of  the  cast  product, 
there  is  always  a  sufficient  difference  in  their  structure,  resulting  from  the 
radical  differences  in  their  methods  of  manufacture,  to  clearly  distinguish 
them  by  simply  examining  the  fracture,  and  to  warrant  a  classification  on 
this  basis  also:  and  this  is  the  customary  basis  of  classification  in  this 
country.*  We  have,  therefore, 

IRON  AND  STEEL  CLASSIFIED  ACCORDING  TO  METHOD  OF  MANUFAC- 
TURE. 
Malleable. 

Wrought  Iron — rolled  or  forged  from  a  puddle-ball;  it  contains 
slag  and  other  impurities,  and  cannot  be  hardened  by  sudden 
cooling. 

Steel — rolled  or  forged  from  a  cast  ingot  and  free  from  slag  and 
similar  matter. 

*  It  has  also  been  recommended  by  a  sub-committee  of  the  recent  French  Commis- 
sion. 


90  THE  MATERIALS  OF  CONSTRUCTION. 

Soft  Steel — will  weld  (with  care),  and  cannot  be  hardened  by 

sudden  cooling  (Ingot  Iron).     Same  uses  as  Wrought  Iron. 

Medium  Steel — will  weld  imperfectly  except  by  electricity),  and 

will  not  harden  by  sudden  cooling.   Used  in  Structural  Work. 

Hard  Steel — will  not  weld,  and  will  harden  by  sudden  cooling. 

Tool-steel,  Spring-steel,  etc. 
Semi-malleable. 

Steel  Castings — Malleable  metal  cast  into  final  forms. 

Malleable  Cast  Iron — non-malleable  metal  cast  into  final  forms 

and  then  brought  to  a  semi-malleable  condition. 
Non-malleable. 
Cast  Iron. 
Hard  Cast  Steel. 

Neither  of  these  classifications  must  be  construed  too  rigidly,  but  they 
fairly  define  the  common  usage,  so  far  as  the  employment  of  these  materials 
in  engineering  design  is  concerned. 

THE   PHYSICAL   PROPERTIES   OF   CAST    IRON. 

61.  General  View. — While  cast  iron  has  been  known  and  commonly  em- 
ployed since  the  Middle  Ages,  it  has  not  been  critically  and  scientifically 
studied  till  within  a  very  few  years.     In  the  last  quarter  of  a  century,  the 
attention   of   metallurgists  engaged  in  iron-manufacturing  industries  has 
been  almost  wholly  confined  to  the  manufacture  of  steel.    The  great  advances 
which  have  been  made  in  this  direction  have  caused  cast  iron  to  be  very 
largely  replaced  by  steel  in  structural  designing,  and  in  other  directions, 
and  since  1885  steel  has  also  been  cast  in  final  forms,  the  same  as  cast  iron, 
so  that  the  use  of  cast  iron  has  been  very  much  diminished,  relatively  to  the 
total  iron  and  steel  output.     For  many  purposes,  however,  cast  iron  will 
probably  never  be  replaced  by  any  other  material,  especially  since  great 
improvements  have  been  made  in  this  direction,  as  a  result  of  scientific 
study  and  experiments  devoted  in  recent  years  to  the  manufacture  of  cast 
iron. 

Much  of  the  matter  here  given  on  this  subject  has  been  quoted  directly 
from  the  Metallurgy  of  Iron  by  Thomas  Turner,  Associate  of  the  Royal 
School  of  Mines,  England.  This  work  was  published  in  1895  and  contains 
the  latest  results  of  scientific  research  on  the  subject  there  treated.* 

62.  General  Properties.—"  Cast  iron  consists  of  metallic  iron,  together 
with  at  least  1.5  per  cent  of  carbon.     It  also  contains  silicon,  sulphur,  phos- 
phorus, manganese,  and  other  elements  in  greater  or  less  proportion,  but 
these  may  be  regarded  as  impurities,  though  their  presence  is  often  useful 
or  even  necessary  for  the  purposes  for  which  cast  iron  is  applied.     The  pro- 

*  When  not  otherwise  credited  the  quoted  paragraphs  are  from  this  work.  (Chas, 
Griffin  &  Co.,  London,  and  Lippincott,  Philadelphia.) 


CAST  IRON.  91 

portion  of  elements  other  than  iron  is  usually  about  7  per  cent  of  the  total 
weight,  though  this  varies  considerably  and  is  sometimes  very  much  more. 
Cast  iron  is  fusible  at  a  temperature  of  about  1200°  C.  (2200°  F.);  when  cold 
it  is  hard  and  brittle,  some  varieties  being  much  more  so  than  others; 
it  is  not  malleable  or  ductile,  like  wrought  iron  or  mild  steel,  nor  can  it  be 
hardened  and  tempered  like  ordinary  carbon  steel,  f^he  iron-founder  distin- 
guishes between  pig  iron,  or  the  form  in  which  the  metal  is  obtained  from 
the  blast-furnace,  and  cast  iron,  or  the  form  it  assumes  after  it  has  been 
again  melted;  but  no  such  difference  is  recognized  by  the  chemist,  and  pjer 
iron  is  merely  a  variety  of  cast  iron  which  is  produced  in  a  particular  formTN 

63.  Carbon  in  Cast  Iron. — "  Cast  iron,  when  fused,  consists  of  a  saturatecTf 
or  nearly  saturated,  solution  of  carbon  in  iron.  The  amount  of  carbon 
which  molten  iron  can  thus  dissolve  is  about  3J  per  cent  of  its  own  weight, 
though  the  solubility  is  largely  influenced  by  the  presence  of  other  elements. 
With  much  chromium  the  maximum  solubility  of  about  12  per  cent  of  car- 
bon is  reached;  with  much  manganese  up  to  7  per  cent  of  carbon  may  be 
dissolved;  while  with  about  20  per  cent  of  silicon  the  minimum  solubility 
of  carbon  is  obtained,  and  only  about  1  per  cent  of  carbon  then  dissolves. 
Apart  from  special  alloys,  such  as  those  mentioned,  it  is  very  unusual  to 
meet  with  less  than  2  per  cent  or  more  than  4.5  per  cent  of  carbon  in  cast 
iron. 

"  So  long  as  iron  containing  some  3  per  cent  of  carbon  remains  in  the 
fluid  condition  the  composition  is  uniform  throughout,  and  the  carbon  has 
no  tendency  to  separate  from  the  metal,  except  with  very  gray  iron;  in  this 
case  a  layer  of  graphite,  which  often  occurs  in  beautiful  plates  and  is  known 
as  kish,  may  be  formed.  But  when  the  molten  cast  iron  is  cooled  to  a  tem- 
perature at  which  it  begins  to  solidify,  it  may  either  retain  tke  carbon  and 
solidify  in  a  relatively  homogeneous  form,  called  white  iron;  or  it  may,  in 
solidifying,  precipitate  the  greater  part  of  the  carbon  in  the  form  of  small 
scales  of  graphite,  which,  being  entangled  by,  and  uniformly  distributed 
through,  the  iron,  impart  to  it  a  somewhat  spongy  nature,  and  produce  the 
dark  color  and  soft  character  met  with  in  gray  iron.  When  about  half  of 
the  carbon  is  precipitated  as  graphite,  and  the  rest  retained  in  combination, 
the  result  is  the  production  of  dark  gray  portions  in  a  matrix  of  white,  and 
the  iron  is  then  said  to  be  mottled. 

"  The  condition  which  the  carbon  assumes  on  the  solidification  of  the 
mass  is  dependent  partly  on  the  rate  of  cooling,  and  still  more  on  the 
nature  and  quantity  of  the  associated  elements.  In  connection  with  the 
influence  of  cooling,  cast  iron  obeys  the  laws  which  govern  other  solu- 
tions, for  it  is  well  known  that  slow  cooling  assists  the  production  of 
crystals,  and  leads  to  the  formation  of  crystals  of  larger  size,  -while  with 
rapid  cooling  both  solvent  and  the  substance  dissolved  may  solidify  together. 
In  a  similar  manner  slow  cooling  tends  to  produce  graphitic  carbon,  and 
the  slower  the  cooling  the  larger  are  the  flakes  of  graphite  which  sepa- 


92  THE  MATERIALS  OF  CONSTRUCTION. 

rate.  Some  kinds  of  white  iron  may  thus  be  rendered  *  gray  by  slow  cool- 
ing, while  some  kinds  of  gray  iron  may  be  made  perfectly  white  by  rapid 
cooling  or  'chilling/  It  is,  however,  only  with  intermediate  irons  that 
the  rate  of  cooling  produces  a  marked  effect,  for  irons  which  are  either 
very  white  or  very  gray  cannot  be  changed  in  this  manner.  The  influence 
exerted  on  the  condition  of  the  carbon  by  the  other  elements  present  in 
cast  iron  is  of  the  greatest  importance;  thus  manganese  and  chromium, 
which  increase  the  solubility  of  carbon  in  iron,  lead  to  a  greater  percentage 
of  total  carbon  in  the  fluid  metal,  and  when  the  iron  solidifies  this  carbon  is 
retained  in  solution,  so  that  irons  rich  in  manganese  and  chromium  are  white 
and  no  amount  of  slow  cooling  will  alter  this  character.  On  the  other  hand,  v 
silicon  and  aluminum  diminish  the  solubility  of  carbon  in  iron;  if  much  of 
either  of  these  elements  be  present  in  the  fluid  metal,  it  is  capable  of  dis- 
solving less  carbon,  and  retains  it  with  less  energy  when  it  solidifies;  as  a 
result  the  carbon  is  precipitated  as  graphite,  and  gray  iron  is  produced. 
Just  as  irons  which  contain  much  manganese  or  chromium  are  permanently 
white,  so  metal  rich  in  silicon  or  aluminum  is  permanently  gray. 

"  The  proportion  of  total  carbon  in  iron  to  be  employed  for  a  given  pur- 
pose is  often  of  secondary  importance;  it  is  governed  by  furnace  conditions, 
and  by  the  proportion  of  other  elements.  A  moderate  alteration  in  total  car- 
bon, or  in  the  graphite,  will  frequently  have  little  effect  on  the  physical 
properties  of  the  product,  while  a  small  change  in  the  combined  carbon 
will  profoundly  alter  the  strength  and  hardness  of  the  casting.  Probably 
no  other  constituent  in  cast  iron  is  of  importance  equal  to  that  of  combined 
carbon,  and  the  influence  of  the  other  elements  is  largely  due  to  the  effect  they 
produce  in  increasing  or  diminishing  the  combined  carbon.  The  following 
percentages  of  combined  carbon  will  usually  be  found  suitable  for  the  pur- 
poses specified: 

*  Combined  Carbon  in 
parts  of  one  per  cent. 

Extra  soft  siliceous  gray  iron 0.08 

Soft  cast  iron 0.15 

Maximum  tensile  strength 0.47 

Maximum  transverse  strength 0.70 

Maximum  crushing  strength over  1.00 

These  figures  are,  however  subject  to  some  variation  according  to  the 
size  of  the  casting  and  the  proportion  of  other  elements.  The  hardness  of 
the  metal  increases  regularly  with  the  increase  of  combined  carbon." 

64.  Silicon  in  Cast  Iron. — "All  cast  iron  contains  silicon,  in  quantities 

*  Chemical  ingredients  of  iron  and  steel  are  always  given  in  hundredths  of  one  per 
cent.  Thus  "  twenty  carbon  "  and  "  eight  phosphorus  "  signifies  0.20  and  0.08  of  one  per 
cent  of  each,  respectively.  Even  the  common  workmen  use  these  terms,  though  they 
may  not  always  understand  them.  The  word  point  is  often  added,  as  "  twenty-point 
carbon." — J.  B.  J. 


CAST  IRON.  93 

varying  in  ordinary  cases  from  under  0.5  to  over  4  per  cent;  while  'silicon 
pig '  is  made  in  the  blast-furnace  with  from  10  to  18  per  cent  of  silicon. 
No  factor  is  of  greater  importance  in  determining  the  suitability  of  a  sample 
of  cast  iron  for  any  purpose  in  the  foundry  than  its  content  of  silicon,  as 
this  element  is  so  constantly  present,  and  its  proportion  is  so.  variable,  while 
the  influence  it  exerts  on  the  condition  of  the  carbon  present,  and  conse- 
quently on  the  hardness  and  fluidity  of  the  rnetal,  is  so  marked.  It  was 
formerly  very  generally  held  that  silicon  was  injurious  in  all  proportions, 
and  the  less  there  was  present  in  iron  for  foundry  purposes  the  better.  It 
is  true  that  Sefstrom  had  observed,  long  ago,  '  that  the  carbon  in  gray  iron 
in  which  much  silicon  exists,  say  from  2  per  cent  to  3  per  cent,  is  wholly, 
or  nearly  so,  in  the  graphitic  state/  *  A  similar  observation  was  made  by 
Snelus  in  1870,  and  was  still  more  plainly  stated  by  Ledebur  in  1879.  It 
was  also  known  in  the  United  States  that  certain  irons  from  Ohio  which 
were  rich  in  silicon  could  be  used  as  '  softeners '  in  foundry  practice,  and 
certain  Scotch  irons -were  in  favor  for  similar  purposes,  though  the  reason 
of  this  was  not  understood.  It  may,  however,  be  claimed  that  no  general  ap- 
plication of  these  facts,  or  accurate  knowledge  of  the  principles  underlying  ' 
them,  existed  before  the  researches  of  the  author,  on  the  '  Influence  of  Sil- 
icon on  the  Properties  of  Cast  Iron/  published  in  1885. f  For  the  purpose 
of  these  experiments  cast  iron  as  free  as  possible  from  silicon  was  specially 
prepared  by  heating  wrought  iron  with  charcoal  to  a  high  temperature  in 
closed  crucibles.  This  was  then  remelted  with  a  silicon  pig  containing 
about  10  per  cent  of  silicon  in  proportions  necessary  to  yield  any  desired 
composition.  The  trials  were  made  with  sufficient  material  to  allow  of 
proper  mechanical  tests  being  performed,  and  a  graduated  series  of  mixtures 
was  prepared.  The  tension,  compression,  and  ductility  tests  were  performed 
by  Professor  A.  B.  W.  Kennedy  with  the  testing-machine  at  University  Col- 
lege, London,  while  the  hardness  determinations  were  performed  by  the 
author  with  a  weighted  diamond  point  (see  Chapter  XVIII)  as  described 
in  his  paper  on  the  '  Hardness  of  Metals/  J  The  chemical  analyses  were 
checked  by  J.  P.  Walton,  at  that  time  chemist  to  the  Glasgow  Iron  Com- 
pany, Wishaw." 

"The  original  pure  cast  iron  was  white,  hard,  and  brittle;  on  adding 
silicon  this  became  gray,  soft,  and  strong;  but  with  a  large  excess  of  silicon 
it  once  more  became  weak  and  hard.  The  results  of  the  mechanical  and 
chemical  tests  are  shown  graphically  in  Fig.  55,  and  it  will  be  observed  that 
the  proportions  of  silicon  corresponding  to  the  various  properties  were  as 
follows: 


*  Percy,  p.  131. 

f  Journ.  Chem.  Soc.,  1885,  pp.  577,  902. 

\  Birm.  Phil.  Soc.,  Dec.  1886. 


94 


THE  MATERIALS  OF  CONSTRUCTION. 


Maximum  hardness under  0.80  per  cent* 

"          crushing  strength about  0.80  " 

"          modulus  of  elasticity "       1.00  " 

"          combined    crushing  and   tensile  strength;    trans- 
verse strength about  1.40  " 

"          tensile  strength ,    "       1.80  " 

"          softness  and  working  qualities, "       2.50  " 

<e         lowest  combined  carbon. .                 under  5.00  " 


2200W 


200000 


/S0000 


\34,00q000\  \ff#,000 

KEYTD  SYMBOLS: 

T£ST0f£0M/>/?/SS/0M  . 

"     »    7FA/3/0M  o    

'  ,  &M$l$ffff£XMM0  x 
*  ,,  Wff.ffffMST.  a 
„  ,,  //JffffA/f?£  m 


44000 


35000 


0 

02  40  8/0 

FIG.  55. — Showing  the  Influence  of  Silicon  on  the  Strength  and  Hardness  of  Cast  Iron, 

(From  Turner's  Iron.) 

"  It  must  be  borne  in  mind  that  these  values  are  only  true  for  the  author's 
experiments.  Experience  has  since  proved  that  these  are  approximately  cor- 
rect in  other  cases,  and  that  the  order  is  as  above  given;  but  in  practice  the* 
size  of  the  casting  and  the  proportion  of  other  elements  will  have  an  impor- 
tant influence."* 

The  influence  of  silicon  on  the  shrinkage  of  cast  iron,  in  various  sizes  tip 
to  4  inches  square,  is  well  shown  in  Fig.  56.  These  results  have  been  well 


*  See  also  Arts.  76  and  79. 


CAST  IRON. 


95 


established  by  Mr.  W.  J-  Keep  of  Detroit.     His  results  of  transverse  tests  of 
strength  and  deflection,  for  varying  proportions  of  silicon,  are  given  iniigs.. 

57  and  58. 


4/40 


a/00 


M70 


0.0S0 


\\ 


& 


m 


.M  .2$  \.30  .4$  .W  & 
1  2"* 


W// 


.30  /.W 


FIG.  56.— Showing  the  Influence  of  Silicon  on  the  Shrinkage  of  Cast-iron  Specimens 
of  Various  Areas  of  Cross-section.     (Keep.) 

"  A  small  addition  of  silicon  eliminates  blowholes  and  produces  sound 
castings.  As  soon  as  the  metal  is  sound,  with  the  least  graphite,  tJie  great- 
est crushing  strength  is  obtained;  this  condition  also  gives  th'e  maximum 
density,  Further  addition  of  silicon  leads  to  the  formation  of  graphite,  di- 
minishes the  brittleness,  and  gives  the  greatest  transverse  and  tensile 
strength.  When  the  graphite  increases  beyond  this  point,  the  metal  is  di- 
vided by  the  interspersed  graphitic  material,  and  the  strength  and  hardness 
decrease.  The  deflection  also  increases  with  the  increase  of  graphite,  but 
when  the  maximum  separation  of  graphite  has  taken  place  any  further  addi- 
tion of  silicon  causes  stiffness  or  brittleness,  and  so  diminishes  the  deflection. 
White  iron  shrinks  during  solidifying  more  than  gray  iron,  while  highly 


96 


THE  MATERIALS  OF  CONSTRUCTION. 


siliceous  iron  shrinks  still  more  than  white.  Hence  on  adding  silicon  to 
white  iron  the  shrinkage  is  diminished,  but  an  excess  of  silicon,  on  the  other 
hand,  leads  to  increased  shrinkage.  Shrinkage  appears  to  closely  follow  the 
hardness  of  cast  iron,  hard  irons  almost  invariably  shrinking  most;  and  as 


<gzw§f 


24000 


II 


2"* 


i0ftW0$6-J£C 


-^" 


0 


FIG.  57.— Showing  Variation  in  Cross-breaking  Modulus  of  Rupture  of  Cast  iron  for 
Different  Sizes  of  Bars  and  for  Varying  Percentages  of  Silicon.     (Keep.) 

both  hardness  and  shrinkage  depend  upon  the  proportion  of  combined  car- 
bon, they  may  be  regulated  by  a  suitable  addition  of  silicon."* 

It  has  been  shown  by  Mr.  Keep  that  the  influence  of  aluminum  on 
cast  iron  is  practically  the  same  as  that  of  silicon,  equivalent  effects 
being  produced,  however,  with  much  smaller  proportions  of  aluminum, 
as  little  as  0.1  per  cent  of  aluminum  causing  the  iron  to  become  soft 
and  graphitic.  Since  the  same  effect  can  be  obtained  by  the  use  of  silicon, 


*  Trans.  Amer.  Inst.  Min.  Eng.,  1888. 


CAST  IRON. 


97 


which  is  much  cheaper,  and  since  the  action  of  the  silicon  is  more  uniform, 
because  of  the  difficulty  of  controlling  the  effects  of  such  small  proportions 
of  aluminum,  the  use  of  aluminum  for  this  purpose  is  not  likely  to  come 
into  general  use. 


70006 


J0000 


3£0W 


•M 


\ 


. 


/- 


^ 


.63 


OF 


2$000 
20000 


FIG.  58.— Showing  the  Variation  in  Transverse  Strength  of  Cast  Iron  in  Various  Sizes- 
of  Cross-section,  up  to  4  in.  square,  due  to  a  Variation  in  Percentage  of  Silicon. 
(Keep,  Tr.  Am.  Soc.  Mech.  Engrs.,  vol.  xvi.i  1895.) 

65.  Sulphur  in  Cast  Iron. — "  The  presence  of  sulphur  in  cast  iron  tends 
to  cause  the  carbon  to  assume  the  combined  form,  and  thus  to  produce  hard, 
weak,  and  brittle  metal.     Such  iron  is  also  unsuitable  for  puddling  and  for 
steel-making,    so  that  hitherto  sulphur   has  been  regarded  as  a  specially 
objectionable  element.     Foundry  iron  of  good  quality  should  not  contain 
more  than  0.15  per  cent  of  sulphur." 

66.  Phosphorus  in  Cast  Iron. — "  The  phosphorus  which  is  present  in 
cast  iron  exists  in  the  form  of  phosphide,  and  is  in  great  part  eliminated 
with -the  excess  of  hydrogen  as  phosphoretted  hydrogen,  when  the  metal  is 
treated  with  dilute  sulphuric  or  hydrochloric  acid.     For  many  purposes, 
such  as  the  manufacture  of  steel  by  either  of  the  acid  processes,  or  the  pro- 
duction of  wrought  iron  for  conversion  into  tool  steel,  it  is  of  prime  impor- 
tance that  the  proportion  of  phosphorus  should  be  as  low  as  possible,  and  the 


98  THE  MATERIALS  OF  CONSTRUCTION. 

maximum  limit  for  such  purposes  is  0.06  per  cent.  It  was  formerly  held 
that  foundry  iron  should  also  be  free  from  phosphorus,  but  the  author  has 
shown  that  cast  irons  of  special  strength  always  contain  a  moderate  propor- 
tion of  this  element.  If  a  large  proportion  of  phosphorus  be  present,  such 
as  from  2  to  5  per  cent,  the  metal  is  very  fluid  when  melted,  and  takes  an 
excellent  impression  of  the  mould.  On  this  account  such  iron  is  sometimes 
employed  for  the  production  of  very  fine  thin  castings,  but  it  cannot  be  used 
for  any  purpose  where  strength  is  required,  as  the  presence  of  so  much 
phosphorus  induces  great  brittleness.  The  brittleness  caused  by  phos- 
phorus is  so  marked  that  a  practical  man  can  often  approximately  tell  the 
percentage  of  phosphorus  by  the  readiness  with  which  the  pig  iron  fractures 
when  dropped  on  the  pig-breaker.  On  the  other  hand,  gray  pig  iron  con- 
taining merely  a  trace  of  phosphorus,  such  as  that  from  the  best  hematite  or 
magnetite  ores,  is  so  soft  and  malleable  as  to  be  somewhat  wanting  int 
strength  and  soundness,  and  hence  gives  inferior  results  for  rolls,  columns, 
girders,  and  other  purposes  for  which  strength  is  necessary.  In  exceptional 
cases  it  is  advantageous  to  have  the  phosphorus  as  low  as  0.20  per  cent  im 
cast  iron,  but  it  is  doubtful  whether  there  is  any  advantage  in  going  below 
this  limit.  For  ordinary  strong  castings  of  good  quality  about  0.55  per  cent 
of  phosphorus  gives  excellent  results.  For  the  general  run  of  foundry 
practice,  where  fluidity  and  softness  is  of  more  importance  than  strength, 
from  1  to  1.5  per  cent  of  phosphorus  may  be  allowed,  but  beyond  this  higher 
limit  the  further  addition/of  phosphorus  causes  such  brittleness  as  to  lead  to« 
marked  deterioration." 

67.  Manganese  in  Cast  Iron. — "  The  proportion  of  manganese  which  is 
met  with  in  iron  produced  in  the  blast-furnace  ranges  from  a  mere  trace  to* 
upwards  of  86  per  cent,  and,  speaking  generally,  the  higher  the  percentage 
of  manganese  the  more  valuable  is  the  product,  on  account  of  the  use  of  this 
element  by  the  steel-maker.  The  physical  properties  of  cast  iron  are  not 
greatly  altered  so  long  as  the  mafr^anese  present  does  not  much  exceed  1  per 
cent,  and  larger  proportions  maj'  6e  present  in  siliceous  iron  without  pro- 
ducing the  appearance  in  the  fracture  which  is  so  characteristic  of  man- 
ganese. When  about  1.5  per  cent  of  manganese  is  present  the  iron  is  very; 
appreciably  harder  to  the  tool,  and  is  more  'suitable  for  smooth  or  polished 
surfaces.  But  when  the  amount  of  ^ilicon  is  relatively  small,  and  the- 
manganese  exceeds  1.5  per  cent,  a  white  iron  is  obtained  with  a  glistening 
fracture  showing  flat  crystalline  plates,  which,  when  very  marked,  leads  to 
the  application  of  the  name  *  spiegeleisen  '  or  mirror  iron,  and  which  is  too- 
hard  to  be  cut  by  cast-steel  tools.  Speigeleisen  contains  up  to  20  per  cent 
of  manganese,  but  with  higher  proportions  the  grain  becomes  once  again 
uniformly  close  and  granular,  and  a  material  is  obtained  which  exhibits  a 
characteristic  light-gray  color,  and  which  is  so  brittle  that  it  may  be  readily 
pounded  in  an  iron  mortar.  To  these  varieties  the  term  *  f erro-manganese ' 
is  applied ;  while  for  some  purposes  an  iron  rich  in  both  silicon  and  man- 
ganese, containing,  for  example,  10  per  cent  of  silicon  and  20  per  cent  of  | 


OAST  IRON.  99 

manganese,  is  produced,  and  is  known  as  *  silicon-spiegel '  or  '  silicon  ferro- 
manganese. ' 

"  From  the  examination  of  the  tests  conducted  at  Woolwich  in  1858,* 
and  numerous  analyses  of  selected  samples  of  cast  iron  of  special  strength, 
the  author  concluded  that  the  presence  of  some  manganese  was  rather  bene- 
ficial than  otherwise  in  foundry  practice,  though  probably  any  benefit  ceases 
when  the  proportion  of  manganese  is  much  greater  than  1  per  cent.f  The 
good  effect  of  manganese  appears  to  be  twofold ;  by  its  own  action  it  leads 
directly  to  a  measure  of  hardness  and  closeness  of  grain  which  is  beneficial, 
while  indirectly  it  is  useful  in  preventing  the  absorption  of  sulphur  during 
remelting. 

"  The  effect  of  manganese  when  alone  is  always  to  harden  cast  iron,  and 
yet  cases  have  come  under  the  author's  notice  in  which  in  actual  practice 
ferro-manganese  has  been  added  in  small  quantity  to  molten  metal  in  a 
foundry  ladle,  with  the  result  that  the  iron  has  been  very  much  softened  and 
improved.  The  reason  for  this  doubtless  lies  in  the  fact  that  manganese 
counteracts  the  effect  of  sulphur  and  silicon,  tending  to  eliminate  the  former 
and  iieutraj^e  the  latter,  and  so,  where  common  iron  is  employed,  it  some- 
times happens  that  ferro-manganese  may  be  used  as  a  softener.  The  hard- 
ness, however,  generally  returns  if  the  iron  be  rernelted,  as  the  manganese  is 
oxidized  and  more  sulphur  absorbed. 

"  Manganese  has  in  this  way  been  employed  as  a  softener^  A  remark- 
able effect  is  produced  on  the  properties  of  hard  cast  iron  by  adding  to  the 
molten  metal,  a  moment  before  pouring  it  into  the  mould,  a  small  quantity 
of  powdered  ferro-manganese,  say  1  Ib.  of  the  latter  to  600  Ibs.  of  cast  iron. 
As  a  result  of  several  hundred  carefully  conducted  experiments  the  trans- 
verse strength  was  increased  30  per  cent,  the  shrinkage  and  depth  of  chill 
decreased  about  25  per  cent,  while  the  combined  carbon  was  diminished  by 
about  one  half.  J  These  observations  accord  with  those  made  by  the  author, 
though  in  all  probability  their  success  defends,  as  above  explained,  on  the 
peculiar  composition  of  the  cast  iron  use 

68.  Grading  of  Pig  Iron. — "  For  commercial  purposes  pig  iron  is  classi- 
fied or  '  graded  '  according  to  the  appearance  of  the  fractured  surface,  the 
first  member  of  the  series  being  taken  as  the  most  open-grained  gray  iron, 
while  white  iron  is  taken  at  the  other  extremity." 

"  In  the  southern  parts  of  the  United  States  the  following  method  of 
grading  pig  iron  into  nine  numbers  was  adopted  in  1889  :§ 


1.  No.  1  Foundry. 
2.  No.  2  Foundry. 
3.  No.  3  Foundry. 

4.  No.  1  Soft. 
5.  No.  2  Soft. 
6.  Silver-gray. 

7.  Gray  Forge. 
8.  Mottled. 
9.  White. 

*  Report,  Cast-iron  Experiments,  1858. 
f  Inst.  Journ.,  1886,  vol.  i.  p.  185, 
t  Jour.  Franklin  Inst.,  Feb.  1888. 
§  Iron  Age,  vol.  XLII.  p.  498. 


100 


TEE  MATERIALS  OF  CONSTRUCTION. 


"  The  following  analyses,  published  by  G-.  L.  Luetscher,  of  the  pig  iron 
made  from  the  ore  of  Red  Mountain,  Alabama,  will  serve  to  illustrate  the 
composition  of  the  different  grades  of  Southern  iron :  * 


Silver 
Gray. 

No  2 

Soft. 

No.  1 
Soft. 

No.  1 
Foun 
dry. 

No.  2 
Foun- 
dry. 

No.  3 
Foun- 
dry. 

Gray 
Forge. 

Mot- 
tled. 

White. 

Graphitic  carbon  
Combined  carbon  
Silicon 

3.13 
.02 
5  5 

3.48 
.03 
3  5 

3'.  53 
.03 

3  75 

3.49 
.07 
3  15 

3.55 

.07 
2  40 

3.48 
.10 

2  20 

3.00 

.57 
1  50 

2.11 
1.22 
1  35 

.10 
292 
95 

Sul  pliur  .  .  ... 

trace 

004 

005 

005 

0°4 

025 

06 

125 

30 

Phosphorus  
Manganese  

.68 
.25 

.68 
.26 

.68 

27 

.68 
25 

.68 
22 

.64 
21    ' 

.64 
19 

.64 

14 

.64 

10 

"  It  will  be  observed  that  the  silicon  regularly  decreases,  with  one  slight 
exception,  from  5.5  per  cent  with  silver  gray,  to  0.95  per  cent  with  white 
iron.  At  the  same  time  the  sulphur  and  combined  carbon  increase  together! 
from  mere  traces  in  silver-gray  iron  to  0.3  per  cent  of  sulphur,  and  nearly  3 
per  cent  of  combined  carbon  in  'white  iron.  The  phosphorus  is  slightly 
lower  with  the  closer  grades.  These  differences  are  exactly  such  as  are 
noticed  with  similar  grades  in  the  United  Kingdom,  the  most  noticeable 
difference  being  the  remarkably  small  quantities  of  sulphur  met  with  in  the 
open-grade  American  iron.  That  American  foundry  irons  have  an  unusually 
low  percentage  of  sulphur  is  a  fact  which  is  supported  by  the  results  of 
numerous  analysts,  and  which  has  not  yet  been  satisfactorily  explained." 

FOUNDRY   PRACTICE. 

69.  "  The  Cupola  is  in  by  far  the  most  general  use  for  remelting  iron.    A* 
cupola  is  a  small  blast-f  nrnace,  of  which  there  £re  many  varieties  employed ; 
they  are  generally  circular  in  section,  and  are  driven  with  low-pressure 
blast  at  or  near  the  atmospheric  temperature.     The  fuel  used  is  generally. 
hard   coke,    though    occasionally   gaseous   fuel    or   charcoal    is   employed. 
Usually  the  melted  metal  collects  at  the  bottom  of  the  cupola,  and  is  tapped 
off  at  intervals;  in  some  cases  separate  receivers  are  adopted. 

"  When  coke  is  used  the  fuel  consumption,  varies  from  about  1£  to  2£ 
cwts.  per  ton  of  iron  melted,  being  greater  with  small  outputs  on  account  off 
the  loss  due  to  heating  the  cupola  with  each  charge.     A  small  quantity  off 
limestone  is  usually  added,  as  it  fluxes  off  the  silica  added  in  the  form  off 
sand  adhering  to  the  pigs,  or  produced  by  the  partial  oxidation  of  the  silicon 
in  the  iron;  it  combines  with  the  ash  of  the  coke,  and  also  diminishes  the 
amount  of  sulphur  which  is  absorbed  from  the  coke  by  the  iron. 

"  The  blast,  which  is  not  heated,  is  driven  by  means  of  a  fan,  or  mor,e 
usually  by  a  blower,  the  pressure  being  only  a  few  ounces  per  square  inch. 
In  the  ordinary  form  of  cupola  the  blast  is  introduced  through  one  or  more' 
tuyeres  in  a  single  row  around  the  zone  of  fusion.     In  Ireland's  cupola, 

*  Inst.  Journ.,  1891,  vol.  n.  p.  245. 


CAST  IRON. 


101 


which  was  introduced  about  1860,  two  rows  of  tuyeres  are  employed,  and  the 
cupola  is  provided  with  boshes  like  a  blast-furnace.  The  object  of  the 
upper  row  of  tuyeres  is  to  insure  more  complete  combustion  of  the  carbonic 
oxide,  which  otherwise  passes  through  the  charge  unburned." 

70.  Influence  of  Remelting. — "  It  is  observed  that  when  cast  iron  is 
remelted  it  becomes  harder  and  more  close  in  texture;  if  the  metal  operated 
be  soft,  the  casting  is  stronger  than  the  original  iron;  but  when  hard  iron  is 
used,  it  becomes  still  harder,  and  weak,  like  ordinary  foundry  scrap.  There 
has  long  been  an  impression  that  remelting  improves  cast  iron,  but  that  this 
is  not  so  is  proved  by  melting  the  metal  in  a  carefully  covered  crucible, 
where  no  change  in  composition  takes  place,  and  the  properties  of  the  iron 
are  unaltered.  In  some  experiments  by  Sir  W.  Fairbairn,*  a  sample  of 
No.  3  Eglinton  gray  iron  was  remelted  in  an  air-furnace  18  times,  test-bars 
being  cast  at  each  melting,  and  it  was  found  that  the  iron  improved  up  to 
the  twelfth  melting,  and  afterwards  rapidly  deteriorated.  -  Other  experi- 
ments were  performed  shortly  afterwards,  in  connection  with  the  manufac- 
ture of  cast-iron  ordnance,  in  which  marked  improvement  was  noticed  on 
remelting  cast  iron,  and  keeping  it  for  a  longer  or  shorter  period  in  a  state 
of  fusion.  No  explanation  of  these  effects  was  given,  but  the  experiments 
were  referred  to  in  numerous  text-books,  and  led  to  the  belief  that  remelting 
per  se  was  beneficial,  though  it  was  observed  that  the  number  of  remel tings 
required  to  produce  the  best  effect  varied  largely  with  different  samples. 

"  By  the  kindness  of  Professor  Unwin,  who  assisted  in  Sir  W.  Fairbairn's 
experiments,  the  author  was  supplied,  more  than  thirty  years  after  the  tests 
were  made,  with  samples  of  the  test-bars,  and  was  enabled  by  their  analysis 
to  clear  up  some  of  the  difficulties  which  had  surrounded  the  subject. f 
The  results  of  the  author's  analyses  were  as  follows: 


No.  of  Melting. 

Total  Carbon. 

Combined. 

Silicon. 

Sulphur. 

Manganese. 

Phosphorus. 

1 

2.67 

0.25 

4.22 

0  03 

1.75 

0.47 

8 

2.97 

0.08 

3.21 

0.05 

0.58 

0.53 

12 

2  94 

0.85 

2.52 

0.11 

0.33 

0.55 

14 

2  98 

1.31 

2.18 

0.13 

0.23 

0.56 

15 

2.87 

1.75 

1.95 

0.16 

0.17 

0.58 

16 

2.88 

1.88 

0.20 

0.12 

0.61 

18 



2  20 





"  It  will  be  noticed  that,  owing  to  the  oxidizing  effect  of  remelting,  the 
proportion  of  silicon  steadily  diminished,  while  sulphur  was  at  the  same 
time  absorbed  from  the  furnace  gases.  The  natural  effect  due  to  these 
changes  was  produced  upon  the  condition  of  the  carbon,  which,  instead  of 
being  almost  wholly  graphitic,  became  nearly  all  combined,  thus  producing 
a  hard,  white  iron,  which  was  deficient  in  tenacity,  and  brittle.  The 

*  B.  A.  Report,  1853,  p.  87. 

f  Journ.  Chem.  Soc.,  vol.  XLTV,  1886,  p.  493. 


102 


THE  MATERIALS  OF  CONSTRUCTION. 


elimination  of  manganese  with  the  silicon,  the  increase  in  the  percentage  of 
phosphorus  due  to  its  concentration  in  a  smaller  quantity  of  metal,  and  the 
initial  increase  of  total  carbon  for  a  similar  reason,  are  all  in  accordance  with 
what  is  observed  whenever  iron  is  melted  in  the  air,  and  when  the  resulting 
slag  is  not  strongly  basic. 

"  The  physical  effects  produced  when  cast  iron  is  remelted  are  thus 
merely  indications  of  chemical  changes  which  have  taken  place  in  the 
material,  while  the  nature  of  these  changes,  and  hence  the  effect  produced 
by  remelting,  will  vary  with  the  composition  of  the  iron  employed  and  the . 
oxidation  to  which  it  is  subjected. 

"  In  Sir  W.  Fairbairn's  experiments  the  metal  was  melted  in  an  air- 
furnace,  but  in  ordinary  practice  a  cupola  is  employed.  Here  the  oxidation 
is  greater,  while  as  the  iron  melts  in  contact  With  the  fuel  it  more  readily 
absorbs  sulphur.  As  a  consequence,  though  the  changes  which  take  place 
are  of  the  same  kind,  and  follow  the  same  order  as  that  previously  given, 
the  effect  of  each  melting  is  more  marked.  This  is  illustrated  by  the  follow- 
ing analyses,*  from  experiments  conducted  by  Jiingst  in  the  Imperial 
Foundry  at  Gleiwitz : 


1st  Melting. 

2d  Melting. 

3d  Melting. 

Carbon,  graphitic  

2  73 

2  54 

2  08 

Carbon,  combined  

66 

80 

1  98 

Silicon  

2  42 

1   88 

1    1fi 

Sulphur     

04 

10 

20 

Phosphorus  

31 

30 

28 

Manganese  

1  09 

44 

36 

71.  Moulds. — "  The  size,  shape,  and  character  of  the  moulds  employee 
in  an  iron  foundry  depend  upon  the  class  of  work  in  hand;  they  may  be 
conveniently  divided  into  the  following  four  classes: 

1.  Green-sand; 

2.  Dry-sand; 

3.  Loam; 

4.  Chills. 

1.  "  Green-sand  moulds  are  made  of  moulding-sand,  which  is  firs 
uniformly  damped,  so  as  to  make  it  adherent,  and  is  lightly  rammed  arounc 
a  pattern  to  obtain  the  required  shape.  For  common  castings,  especially 
when  of  large  size,  open  sand  is  often  used;  but  for  the  majority  of  purpose 
the  sand  is  contained  in  boxes,  which  in  the  United  Kingdom  are  usually  o 
cast  iron,  though  wooden  moulding-boxes  are  generally  used  in  the  Unite* 
States.  Usually  there  are  two  boxes,  upper  and  lower,  the  pattern  o 
patterns  being  placed  partly  in  each  box,  and  the  '  gate  '  or  opening  for  th 
entry  of  the  metal  being  commonly  in  connection  with  the  middle  of  th 

*  List.  Journ.,  1885,  vol.  n.  p.  645. 


CAST  IRON.  103 

castings.  Where  a  hole  or  passage  is  required  in  the  casting,  a  '  core  '  is 
employed;  this  generally  consists  of  sand,  moulded  into  the  necessary  shape, 
and  supported  by  iron  wire  or  other  suitable  means.  The  patterns  are 
generally  of  wood,  and  if  of  intricate  forms,  are  made  in  parts  designed  to 
allow  of  their  removal  from  the  mould;  the  several  parts  are  kept  in  position 
by  suitable  pins.  Green-sand  moulding  is  the  process  most  generally 
adopted,  as  it  is  rapid  and  cheap;  it  involves  the  use  of  no  expensive  plant, 
and  is  specially  suitable  for  the  production  of  a  large  number  of  articles  of 
similar  form.  Machine  moulding  is  employed  by  manufacturers  who  have 
a  considerable  demand  for  one  class  of  work,  and  in  such  cases  sand-mould- 
ing machines  are  coming  steadily  into  favor,  though  they  can  never  replace 
hand  work  in  a  general  foundry. 

2.  "  Dry-sand  moulds  are  made  of  a  loamy  sand  which,  after  being 
roughly  moulded  into  shape,  is  dried  by  heat,  and  then  carefully  finished 
with  the  tool.     The  mould  is  sufficiently  soft  to  be  readily  cut,  though  rigid 
•enough  to  retain  its  shape  when  the  molten  metal  is  poured  into  it.     Such 
moulds  have  the  advantage  of  giving  sounder  castings,  as  they  evolve  less 
gas,  while  where  a  single  casting  is  needed  they  save  money,  as  no  pattern  is 
required.     When,  however,  a  pattern  has  once  been  prepared,  green-sand 
moulds  are  much  cheaper. 

3.  "  Loam-moulds  are  more  particularly  employed  for  curved  or  spiral 
surfaces  of  large  size,  such  as  sugar-pans,  '  copper  '  boilers,  soda-pans,  water- 
pipes,  etc.     The  outer  part  of  the  mould  is  either  built  up  of  brickwork, 
held  in  place  with  iron  ties;    or  where   a   number  of  similar  articles  is 
required,  an  iron  casing  is  employed.     The  inner  surface  of  the  mould  is 
made  of  loam,  which  is  laid  on  by  the  trowel,  and  worked  by  the  hand,  and 
usually  faced  with  some  carbonaceous  blacking.    The  whole  is  then  carefully 
dried  before  use,  one  of  the  most  general  methods  being  by  the.introduction 
of  a  flame  of  gas  into  the  interior.     Such  moulds  can,  of  course,  only  be 
employed  for  one  casting,  and  the  labor  and  cost  of  loam-moulding  is  much 
greater  than  that  of  green-sand. 

4.  "  Chills  are  used  when  it  is  desired  to  produce  a  casting  the  outside 
of  which  is  unusually  hard.     The  iron  used  is  generally  a  close-grained 
gray,  and  this  is  converted  into  white  iron  where  it  comes  in  contact  with 
the  cold  side  of  the  mould  during  solidification.     A  familiar  example  of  the 
use  of  chills  is  met  with  in  the  production  of  chilled  rolls  and  car-wheels. 
Rolls  are  cast  on  end,  with  a  good  head  of  metal,  so  as  to  give  soundness, 
while  as  the  shanks  of  the  roll  are  required  to  be  turned  to  size,  these  are 
cast  in  sand,  and  are,  therefore,  relatively  soft.     The  intermediate  part  of 
the  mould,  in  which  the  barrel  of  the  roll  is  cast,  is  made  up  of  a  number  of 
large  annular  rings  of  cast  iron  resting  one  upon  another.     These  are  not 
used  cold,  or  a  violent  explosion  would  take  place  when  the  hot  metal  came 
in  contact  with  the  cold,  and   therefore  probably  slightly  clamp,  chilling 
surface.     The  mould  is,  on  this  account,  heated  to  a  temperature  of  about 
150°  to  200°  C.  before  the  metal  is  introduced,  and  the  iron  is  caused  to  enter 


104  THE  MATERIALS  OF  CONSTRUCTION. 

from  the  bottom,  and  in  an  oblique  direction.  By  this  means  a  circular 
motion  is  imparted  to  the  metal,  and  thus,  as  it  rises,  it  collects  all  dirt 
and  impurities  on  its  surface,  and  so  fills  every  crevice  of  the  mould." 

72.   Moulding-sand. — "  The  proper  selection  and  preparation  of  mould- 
ing-sand has  an  important  influence  on  the  appearance  and  quality  of  the 
castings  produced  in  the  foundry.     The  mould  must  be  capable  of  retaining 
the  fluid  metal  in  every  direction,  but  at  the  same  time  it  must  allow  of  the 
free  passage  of  the  air  which  is  collected,  and  the  gases  which  are  generated 
when  the  mould  is  filled  with  hot  iron.     It  must  give  to  the  casting  a 
smooth,  clean  surface,  and  hence  must  neither  act  upon,  nor  be  affected  by,  j 
the  fluid  metal  at  the  high  temperature  at  which  they  are  brought  in  con- 
tact ;  the  higher  the  temperature  is  that  is  necessary  to  retain  the  metal  in  \ 
the  perfectly  fluid  condition,  the  greater  is  the  difficulty  of  complying  with 
this  condition.     Thus  moulds  for  cast  iron  require  more  careful  preparation 
than  those  for  brass,  while  those  to  be  employed  for  steel  castings  require 
still   more   careful   attention.       Moulding-sands    consist    chiefly   of    silica, 
together  with  variable  proportions  of  alumina,  magnesia,  lime,  and  other ? 
metallic  oxides;  coal-dust  is  also  frequently  added  in  small  quantity.     The 
higher  the  proportion  of  silica  the  more  refractory  the  sand  becomes;  but' 
it  is  then  apt  to  be  wanting  in  cohesion,  and  to  be  difficult  to  mould,  while* 
the  moulds  crack  in  drying,  or  are  injured  by  the  flow  of  metal.     Alumina 
and  magnesia  impart  cohesion  and  plasticity,  though  excess,  especially  0$ 
alumina,  causes  it  to  be  less  refractory.     Magnesia  is  refractory,  forming  a 
good  cement  for  siliceous  sand,  but  when  present  in  quantity  it  renders  the* 
mould  less  porous.     Lime  and  other  metallic  oxides  render  sand  less  refrac- 
tory, and  should  be  avoided  as  far  as  possible.     If  the  lime  be  present  as 
carbonate,  gas  will  be  given  off  at  high  temperatures,  and  will  produce  rough 
surfaces  in  the  casting;  while  if  it  be  present  as  silicate,  it  will  cause  thai 
sand  to  adhere  to  the  surface  of  the  hot  metal.     According  to  Kohn,*  at 
suitable  composition  for  green-sand  moulding  is  approximately  as  follows: 
Silica,  92  per  cent;  alumina,  6  per  cent;  oxide  of  iron,  1.5  per  cent;  ancfci 
lime  0.5  per  cent;  while  sand  for  stove-dried  moulds  is  usually  richer  im 
alumina  and  oxide  of  iron.     According  to  the  same  author,  a  composition! 
largely  used  in  steel-works  for  moulding  purposes  is 'prepared  from  Sheffield) 
ganister,  which  is  mixed  with  sufficient  magnesia  and  alumina  to  give  a; 
product  containing  about  85  parts  of  silica,  5  to  10  of  alumina,  and  5  to  10 
of  magnesia. 

"  In  addition  to  the  sand  being  of  the  right  chemical  composition,  which 
condition  affects  its  plasticity  and  refractory  nature  as  above  indicated,  it  is 
also  necessary  that  it  should  be  of  proper  degree  of  fineness,  as  when  the 
particles  are  too  coarse  the  surface  of  the  castings  is  inferior,  and  the  sand  is 
wanting  in  cohesion,  while  when  the  sand  is  unusually  fine  it  is  unsuitable 
for  large  castings,  as  the  gases  cannot  so  readily  escape." 


*  Iron  Manufacture,  p.  55. 


PLATE  III. 


«t 


HIDDEN  DEFECTS  IN  A  CAST-IKON  COLUMN  DISCOVERED  AFTER  THE  BUILDING  HAD 

BEEN  ERECTED. 


•^^'S^^^^^";-V'':^PKHHHHI  I 

AILURE  OF  A  STEEL  STAND  PIPE  DUE  TO  BRITTLE  BESSEMER-STEEL  PLATES  IN  TIIK 
Two  LOWER  COURSES,  THE  INITIAL  RUPTURE  SHOWN  IN  THE  FOREGROUND. 
The  tensile  stress  on  the  net  section  at  time  of  failure  was  only  one  fifth  the  ultimate 
strength  of  the  metal.     (Examined  and  photographed  by  the  author.) 


CAST  IRON.  105 

73.  Effect  of  Size  and  Shape. — "  The  strength  and  solidity  of  a  casting  are 
affected  by  the  bulk  of  metal  employed,  and  by  the  form  of  casting  made. 
Thus  if  a  sample  of  pig  iron  which  would  be  suitable  for  a  casting  of  small 
size  be  employed  for  making  very  heavy  work,  it  will  be  found  that  owing 
to  the  slower  cooling  in  the  latter  case  the  grain  of  the  metal  becomes  much 
more  open,   and  the  strength  is  proportionally  diminished;  on  the  other 
hand,  if  the  same  metal  were  used  for  very  small  castings,  the  chilling  m  the 
mould  would  tend  to  make  the  product  close  and  hard,  and  in  many  cases 
this  would  be  so  marked  as  to  make  the  castings  quite  brittle.     The  grade  of 
the  iron  used  must  therefore  depend  upon  the  size  of  the  casting  to  be  made, 
the  general  rule  being  that  a  closer-grained  or  less  siliceous  iron  must  be  used 
for  krge  than  for  small  castings.     At  the  same  time  it  is  generally  found 
that\he  strength  of  a  large  casting  per  unit  of  area  is  somewhat  less  than 
that  oj:  a  smaller  one,  since  the  closeness  of  grain  is  usually,  though  not 
always,  associated  with  increased  tenacity. 

"It  is  also  very  important  that  in  large  castings,  where  strength  is 
required,  no  .sharp  or  re-entering  augles  should  occur,  as  these  in  all  cases 
lead  to  the  formation  of  planes  of  weakness  in  the  casting.  When  the  metal 
cools  in  the  mould  a  crystalline  structure  is  developed,  the  crystals  forming 
at  right  angles  to  the  cooling  surface.  If  this  cooling  surface  be  curved,  the 
crystals  interlace  so  as  to  yield  a  strong- casting  of  uniform  structure,  while, 
on  the  other  hand,  whenever  a  sharp  angle  of  curvature  takes  place  a  plane 
of  weakness  is  the  result. ' ' 

Cast-iron  columns,  used  in  architectural  construction,  are  commonly  cast 
in  a  horizontal  position,  thus  offering  a  very  poor  means  of  escape  for 
loosened  sand,  cinder,  etc.,  which  foreign  matter  often  collects  on  the  upper 
side  and  greatly  weakens  the  column.  Furthermore,  these  are  often 
covered  by  a  thin  coating  of  iron.  Such  faults,  found  in  many  columns 
which  had  been  accepted  and  used  *  in  a  public  building  in  St.  Louis,  are 
shown  in  Plate  III. 

74.  Shrinkage  of  Cast  Iron. — "  Although  cast  iron,  especially  when  very 
gray,  expands  at  the  moment  of  solidification,  and  thus  gives  a  sharp  im- 
pression of  the  mould,  the  subsequent  cooling  from  a  red  heat  to  the  ordinary 
temperature  leads  to  a  still  greater  contraction,  and  the  net  result  is  that  the 
casting  is  always  smaller  than  the  pattern  from  which  it  is  made.     For  this 
reason  it  is  usual  in  pattern-making  to  allow  about  ^  of  an  inch  per  foot  for 
shrinkage,  and  if  the  casting  is  required  1  foot  long,  the  pattern  is  made  1 
foot  and  -J  of  an  inch  in  length.     The  shrinkage  in  castings  is,  however,  by 
no  means  a  constant  quantity,  but  varies  with  the  relative  dimensions  of  the 
castings  and  with  the  character  of  the  metal  used ;  as  much  as  y^  of  an  inch 
per  foot  being  allowed  when  casting  beams,  and  only  -fa  with  large  cylinders. 
Not  unfrequently  much  loss  and  inconvenience  is  occasioned  in  foundry 
work  by  variations  in  the  shrinkage,  caused  by  altering  the  shape  or  propor- 
tions of  a  pattern,  or  by  the  use  of  a  different  variety  of  iron. 

*  They  were  removed  after  the  faults  were  discovered. 


106  THE  MATERIALS  OF  CONSTRUCTION. 

"  In  the  author's  experiments  on  cast  iron  it  was  noticed  that  silicon  pig 
shrank  most  in  the  mould,  though  no  accurate  determinations  of  shrinkage 
were  made.  The  subject  has  since  been  carefully  investigated  by  W.  J. 
Keep,  of  Detroit,  whose  experiments  embody  the  whole  of  the  trustworthy 
data  available,  and  who  measures  shrinkage  by  casting  bars  in  sand  between 
iron  chills  12£  inches  apart.  The  contraction  is  carefully  measured  by 
means  of  graduated  wedges  which  are  inserted  between  the  ends  of  the  cold 
bar  and  the  iron  chill  in  which  the  bar  was  cast.  Mr.  Keep  concludes  that 
when  silicon  varies,  and  other  elements  do  not  vary  materially,  castings  with 
low  shrinkage  are  soft,  and  that  as  shrinkage  increases,  hardness  increases  in 
almost,  if  not  exactly,  the  same  proportion.  For  ordinary  foundry  practice 
the  scale  of  shrinkage  agrees  with  the  scale  of  hardness,  so  long  as  sulphur 
and  phosphorus  do  not  vary  over  wide  limits.  This  is  an  important  fact; 
and  as  shrinkage  tests  are  very  easily  performed  by  an  ordinary  workman, 
the  subject  is  worthy  of  more  attention  than  it  has  hitherto  received."  * 

-  "It  is  stated  that  charcoal  iron  has  usually  a  melting-point  which  is 
considerably  higher  than  that  of  less  pure  iron  made  with  coke.  Charcoal 
iron,  therefore,  sets  more  quickly  in  the  mould,  and  contracts  more,  so  that 
an  extra  allowance  for  shrinkage  must  be  made  in  the  patterns  employed."  f 

THE    MECHANICAL   PROPERTIES   OF   CAST   IRON. 

75.  "  Hardness  of  Cast  Iron. — The  hardness  or  softness  of  cast  iron  is  in 
many  instances  of  the  greatest  importance,  as  the  metal  has  to  be  turned, 
planed,  filed,  or  otherwise  worked  with  tools;  hence  a  number  of  methods 
have  been  devised  at  various  times,  with  the  object  of  determining  relative 
hardness.  In  the  older  form  of  apparatus,  such  as  was  used  by  the  American 
Ordnance  Commissioners  in  1856,  an  indentation  was  made  in  the  surface  of 
the  metal  to  be  tested.  By  determining  either  the  force  required  to  make 
a  hole  of  a  given  size,  or,  on  the  other  hand,  the  size  of  the  indentation 
produced  by  a  given  force,  a  measure  of  hardness  was  sought  to  be  obtained. 
Such  a  method  is,  however,  erroneous  unless  the  tenacity  of  all  the  specimens 
to  be  examined  is  the  same,  as  otherwise  a  deeper  hole  will  be  produced  ia 
the  weaker  metal,  irrespectively  of  hardness.  J  In  the  author's  researches  &j 
weighted  diamond  was  employed  for  determining  the  hardness  of  cast  iron, , 
and  the  results  obtained  with  increasing  proportions  of  silicon  are  graphically 
represented  in  Fig.  55.  When  very  little  silicon  was  present  the  metal  was  < 
extremely  hard  owing  to  the  large  proportion  of  combined,  carbon,  while 
when  sufficient  silicon  had  been  added  to  convert  the  greater  part  of  the  •> 
carbon  into  the  graphitic  form  the  maximum  softness  was  obtained.  With 
further  additions  of  silicon  the  metal  became  harder  owing  to  the  hardening 
effect  of  silicon  itself,  and  for  this  reason  an  excess  of  silicon,  beyond  about 
3  per  cent,  is  injurious  to  the  working  qualities  of  the  metal." 

*  W.  J.  Keep,  Silicon  in  Cast  Iron,  p.  22.          \  Kohn,  Iron  Manufacture,  p.  57. 
\  The  French  Commission  recommend  this  tesc  for  hardness,  using  impacts  of  known 
value  in  place  of  static  pressure.     See  Chap.  XVIII.  —  J.  B.  J. 


CAST  IRON. 


107 


76.  Hardness  and  Strength  of  Cast  Iron. — "  When  cast  iron  has  to  be 
turned  or  otherwise  worked  the  hardness  is  of  considerable  importance, 
while  in  some  cases  smoothness  of  surface  and  general  perfection  of  the  cast- 
ing are  of  the  utmost  moment.  Hard  cast  iron  is  brittle,  deficient  alike  in 
crushing,  transverse,  and  tensile  strength,  and  seldom  gives  smooth  clean 
castings.  With  metal  which  is  a  little  less  hard  the  maximum  crushing 
strength  is  obtained;  while  on  rendering  it  a  little  softer,  or,  as  the  workman 
would  call  it,  '  moderately  hard,'  the  maximum  transverse  strength  is 
observed.  With  slightly  softer  cast  iron  the  highest  tensile  tests  are 
obtained,  while  still  softer  metal  works  with  the  utmost  facility,  though  it  is 
deficient  in  strength.  It  will  be  seen,  therefore,  that  when  the  general 
connection  between  hardness  and  strength  has  been  fully  grasped,  the  iron- 
founder  requires  only  the  information  how  to  harden  or  soften  his. metal  at 
will,  by  the  use  of  silicon  or  other  agents,  to  be  able  to  produce  castings  in 
which  crushing,  transverse,  or  tensile  strength  shall  predominate  as  desired, 
or  in  which  softness  and  fine  surfaces  shall  be  the  most  characteristic  feature. 

"  There  is  a  somewhat  prevalent  idea  among  founders  that  if  considerable 
strength  is  required  a  hard  iron  must  be  employed.  Doubtless  this  is  to  some 
extent  true  in  connection  with  crushing  and  transverse  tests,  but  is  certainly 
not  correct  with  tensile  strength.  In  all  specimens  of  exceptionally  high 
tensile  strength  examined  by  the  author  the  metal  was  a  soft  good  working 
iron,  specially  suited  for  engineers'  purposes.  In  the  accompanying  table 
is  a  summary  of  the  author's  results  on  the  tenacity  and  hardness .  of  cast 
iron,  as  affected  by  alterations  in  the  proportion  of  silicon.*  The  working 
qualities  of  the  specimens  are  also  given,  and  it  will  be  seen  that  the  hard- 
ness as  determined  by  the  sclerometer  agrees  very  closely  with  the  observa- 
tions of  the  workman.  It  will  be  noticed,  however,  that  hardness  and 
tensile  strength  do  not  vary  together,  but  on  the  contrary  high  tensile 
strength  is  met  with  in  the  softer  irons." 


TABLE     I. — INFLUENCE    OF    SILICON    ON    THE 

OF   CAST   IRON. 


HAEDNESS    AND    TENACITY 


Tensile 

Hardness 

No. 

Silicon 
per  cent. 

Strength 
in  Lbs.  per 

by 
Sclerom- 

Working Qualities,  as  determined  by  the  Workman. 

Sq.  In. 

eter. 

• 

1 

0.19 

22,700 

72 

Very  bard  indeed. 

2 

0.45 

27,600 

52 

Very  hard,  though  not  so  hard  as  No.  1. 

3 

0.96 

28,500 

42 

Hard,  though  softer  than  No.  2. 

4 

1.96 

35,200 

22 

Good,  sound,  ordinary,  soft-cutting  iron,  of  ex- 

cellent quality. 

5 

2.51 

32,800 

22 

Rather  harder  than  No.  4. 

6 

2,96 

27,400 

22 

Like  No.  4. 

7 

3.92 

25,300 

27 

Like  No.  6,  but  rather  harder. 

8 

4.75 

22,700 

32 

Rather  harder  than  No.  7,  though  not  unusually 

hard. 

9 

7.37 

12,000 

42 

Still  harder,  cutting  very  like  No.  10. 

10 

9.80 

10,600 

57 

Hard-cutting  iron,  though  still  softer  than  No.  1. 

*  Journ.  Cliem.  Soc.,  1885^ 


108 


THE  MATERIALS  OF  CONSTRUCTION. 


77.  Crushing  Strength. — "  Cast  iron  possesses  an  exceptionally  high 
crushing  strength,  and  for  the  majority  of  purposes  the  founder  relies  upon 
this,  and  does  not  perform  special  tests.  Usually  the  tensile  strength  is  not 
above  one  sixth  of  the  crushing  strength ;  hence  if  power  to  resist  a  tensile 
force  is  assured,  the  crushing  strength  is  usually  sufficient  for  ordinary  work, 
In  performing  compressive  tests  it  is  necessary  to  have  perfectly  parallel  sur- 
faces, and  to  bed  the  specimen  as  true  as  possible,  otherwise  the  results  will 
be  low." 

As  shown  in  Articles  19  and  22,  the  height  of  a  crushing-test  specimen 
of  such  a  material  as  cast  iron  should  be  not  less  than  about  twice  its 
least  lateral  dimension.  Test  specimens  of  cast  iron  are  usually  cylinders 
which  have  been  turned  up  in  the  lathe,  and  hence  the  length  of  such  a 
specimen  should  be  not  less  than  twice  the  diameter."  The  following  table 
of  values  contains  the  results  of  a  great  many  tests  of  cast  iron  in  compression 
on  short  cylinders,  the  dimensions  being  usually  one  inch  in  diameter  and 
from  two  and  one-half  to  three  inches  high. 

TABLE   II. — CRUSHING    STRENGTH   OF   CAST   IRON. 


Experimenters. 

Pounds  per  Square  Inch. 

Authorities. 

Max. 

Min. 

Mean. 

Hod°"kinson 

146,000 
121,000 
140,000 
215,000 
207,000 

82,000 
55,000 
44,500 
92,000 
77,000 

107,000 
86,000 
91,000 

Pairbairn,  Iron,  1869,  p.  218. 
Pole,  Iron  Construction,  p.  84. 
Report,  1858,  p.  2. 
B.  A.  Report,  1853,  p.  87. 
J.  Chem.  Soc.,  1885,  p.  907. 

Hodgkiiison  (1849)  
Woolwich  (1858)  
Fairbairn  
Turner 

"  The  average  crushing  strength  of  British  cast  iron  is  thus  about  90,000 
Ibs.  per  square  inch;  exceptionally,  results  so  low  as  45,000  Ibs.  have  been 
observed,  while,  on  the  other  hand,  a  strength  of  upwards  of  200,000  Ibs. 
has  been  produced  in  some  instances.  In  the  above  experiments  no  special 
pains  were  taken  to  produce  an  iron  possessing  a  high  crushing  strength;  on 
the  contrary,  only  such  irons  were  taken  as  were  met  with  in  commerce. 
In  the  light  of  modern  researches,  iron  could  doubtless  be  produced  with  a 
crushing  strength  of  225,000  Ibs.  to  the  square  inch,  while  a  strength  of 
150,000  Ibs.  could,  if  necessary,  be  regularly  assured.  A  series  of  sketches 
illustrating  the  fractures  of  test-pieces  with  different  proportions  of  silicon, 
when  subject  to  a  compressive  force,  are  given  in  the  author's  paper  on 
'  Silicon  in  Cast  Iron.'  *  The  samples  were  prepared  by  the  author,  and  the 
mechanical  tests  performed  by  Professor  Kennedy  at  University  College. 
From  these  experiments  it  is  probable  that  the  maximum  crushing  strength 
would  be  obtained  with  about  0.75  per  cent  of  silicon  and  2  percent  of 
combined  carbon." 


*  Journ.  Chem.  Soc.,  1885,  p.  909. 


<3- 


CAST  IRON. 


109 


78.  Transverse  Strength. — "  As  before  stated,  the  maximum  transverse 
strength  is  obtained  with  metal  a  little  softer  than  that  which  possesses  the 
highest  crushing  strength.  Transverse  strength  depends,  at  least  in  part, 
on  the  power  to  resist  both  a  crushing  and  a  tensile  force;  hence  transverse 
strength  is  intermediate  between  crushing  and  tensile  so  far  as  the  charactei 
of  the  iron  is  concerned.  This  combination  of  properties  imparts  to  the 
metal  characters  which  are  most  valuable  in  certain  cases.  For  transverse 
tests  many  shapes  and  sizes  of  test-bar  have  been  adopted,  and,  for  scientific 
purposes,  the  results  so  obtained  are  converted  by  calculation  into  breaking- 
stress  on  the  extreme  fibres  in  pounds  per  square  inch,  which  is  called 
the  modulus  of  rupture.  See  Art.  33.  For  a  load  in  the  centre  of  a 

3   PI 

rectangular  bar  we  have/  =  -  c-y^,  where 

/v   bli 

f  —  modulus  of  rapture  in  cross-breaking; 
P  =  breaking  load,  at  centre ; 
I  —  length  of  bar  in  inches ; 
1)  =  breadth  of  bar  in  inches; 
li  —  height  of  bar  in  inches. 

^ 

TABLE  III. — MODULUS  OF  RUPTURE  OF  CAST  IRON. 


Modulus  of  Rup- 

ture in  Pounds 

Experimenters. 

per  Square  Inch. 

f  =  llL. 

Authorities. 

Robert  Stephenson,  1847.  .  . 

(  Max. 
/  Min  . 

58,000 
37,000 

Pole,  Iron  for  Construction,  p. 

88. 

(  Max. 

47,500 

Hodgkinson  and  Fairbairn. 

•j  Min 

29,500 

Box,  Strength  of  Materials,  p. 

186. 

(  Mean 

37,000 

* 

(  Max. 

42,500 

Woolwich   1858  

•j  Miu  . 

9,700 

Report,  p.  2. 

(  Mean 

20,700 

Fairbairn    1853           .... 

.     Max. 

50  000 

B.  A.  Report  1853,  p.  87. 

Turner   1885  

.  .  .  Max. 

03,500 

Inst.  Journ.,  1886,  p.  1. 

"  It  will  be  noticed  that  the  modulus  of  rupture  varies  from  the  excep- 
tionally low  value  of  9700  Ibs.  to  63,500  Ibs.  The  average  for  common  iron 
is  about  30,000,  while  45,000  is  required  for  better-class  castings.  Foi 
specially  good  work  some  South  Staffordshire  founders  can  produce  u 
strength  of  60,000  with  tolerable  regularity.  In  performing  transverse  tests. 
care  should  be  taken  to  avoid  even  the  slightest  twist  on  the  specimen,  and 
the  weights  used  should  be  added  very  gradually,  otherwise  low  and  irregular 
results  are  obtained.  The  size  of  bar  used  has  also  an  influence  on  the 
strength  (as  shown  in  Figs.  57  and  58),  the  smaller  sectional  areas  giving 
much  higher  values.  It  should  be  remembered  that  the  strength  of  a  test- 
bar  does  not  accurately  represent  the  strength  to  be  expected  in  the  casting, 
if  the  size  of  the  latter,  and  the  circumstances  of  pouring,  do  not  pretty 
closely  agree  with  those  of  the  test-bar  itself." 


110 


THE  MATERIALS  OF  CONSTRUCTION. 


79.  Tensile  Strength. — "  In  many  of  the  less  important  foundries  tensile 
tests  are  omitted,  but  in  the  better  works  such  tests  are  generally  performed, 
and  appear  to  be  growing  in  favor.  It  was  shown  by  the  American  Ordnance 
Experiments  (1856)  that  the  tenacity  of  cast  iron  usually  serves  as  a  guide 
to  its  mechanical  value,  and  practical  experience  quite  confirms  this  view. 
Tensile  test-pieces  are  of  various  forms:  they  are  sometimes  used  with  the 
skin  on,  at  others  the  surface  is  carefully  turned ;  sometimes  small  pieces  are  • 
cast  separately,  while  other  founders  cast  the  pieces  on  to  the  object  which 
is  being  made.  At  Rosebank  Foundry,  Edinburgh,  the  practice  is  to  cast  a 
test-piece-on  to  the  top  and  bottom  of  each  important  article;  these  pieces 
are  afterwards  broken  off,  and  carefully  turned  down  to  a  suitable  size  before 
breaking.  Such  a  method  is  calculated  to  give  a  result  very  nearly  approach- 
ing what  may  be  expected  in  the  casting  itself;  for  not  only  is  the  test-piece 
of  the  same  composition  as  the  casting,  but  it  is  also  cast  under  as  nearly  as 
possible  the  same  conditions  as  to  temperature,  pressure  of  metal,  and  rate 
of  cooling,  all  of  which  have  a  considerable  effect  on  the  strength  of  the 
product. 

"  The  follbwing  table  condensed  from  a  paper  by  the  author  will  serve 
to  illustrate  the  results  obtained  by  different  observers :  * 

TABLE   IV. — TENSILE   STRENGTH    OF    CAST   IRON. 


Experimenters. 

Pounds  per  Square  Inch. 

Authorities 

Max. 

Min. 

Mean. 

Minard  and  Desnormes,  1815  .... 
Hodgkinson  and  Fairbairn,  1837. 
"      ,  1849. 
Woolwich   1858  

20,300 
22,000 
23,500 
34,300 
35,200 
40,800 

12,200 
13,400 

9,200 
10,600 

16,000 
16,800 
15,300 
23,300 

Tredgold,  4th  Ed.,  p.  230. 
B.  A.  Report,  1837,  p.  339. 
Pole,  Iron  Construction,  p.  79. 
Report,  1858,  p.  2. 
J.  Chem.  Soc.  ,  1885,  p.  580. 

Turner,  1885  

Rosebank   1886        

"  It  will  be  seen  that  the  highest  tensile  strength  of  British  iron  above 
recorded  (40,800  Ibs.)  was  obtained  in  the  experiments  at  Rosebank  Foundry 
in  1886.  The  average  tensile  strength  obtained  by  earlier  experimenters 
was  about  16,000  Ibs.,  while  in  1858  the  mean  was  raised  to  23,000  Ibs. 
This  increase  represents  a  real  improvement  in  the  metal  tested,  and  was  due 
to  a  selection  of  the  more  suitable  irons  as  a  result  of  increased  knowledge. 
Foundry  practice  has  since  improved,  and  some  engineers  now  stipulate  that. 
a  bar  one  inch  in  section  shall  be  capable  of  bearing  a  weight  of  22,400  Ibs. 
for  twenty-four  hours  without  fracture,  and  this  apparently  severe  test  has. 
been  complied  with.  Contracts  are  now  satisfactorily  executed  in  which  a 
minimum  strength  of  27,000  Ibs.  per  square  inch  is  required,  and  to  produce 
this  nothing  but  Cleveland  iron  is  employed.  The  author  has  also  succeeded 
in  regularly  producing  an  iron  of  excellent  working  qualities,  with  a  tensile 


*/.  S.  C.  I.,  vol.  v.  p.  289. 


CAST  IRON. 


Ill 


strength  of  29,000  Ibs.  per  square  inch,  from  a  mixture  costing  under  two 
pounds  (ten  dollars)  per  ton,  and*  consisting  of  cast-iron  scrap  and  siliceous, 
iron.  This  is  a  striking  instance  of  the  value  of  combined  chemical  arid 
mechanical  knowledge  to  the  iron-founder. 

"  In  foreign  cast  iron  some  tensile  strengths  .have  been  recorded  which 
have  not  yet  been  equalled  in  Britain,  though  probably  these  results  are  to 
be  regarded  as  quite  exceptional.  Thus  Professor  Ledebur  records  a  tensile 
strength  of  42,700  Ibs.  per  square  inch  with  German  iron,*  while  the  Ameri- 
can Commission  on  Metal  for  Cannon,  in  1856,  obtained  a  maximum  of 
46,000  Ibs.,  and  at  the  Wassiac  furnaces,  New  York,  47,500  Ibs.  have  been 
obtained. f  Much  difference  of  opinion  has  been  expressed  as  to  the  value 
of  tensile  tests  for  cast  iron,  as  the  metal  is  now  never  used  in  tension. 
Professor  Ledebur,  who  is  probably  the  best  authority  on  this  subject  in 
Germany,  states  that  tensile  tests  should  always  be  made ;  and  the  author's 
experience  leads  to  the  conclusion  that  where  a  complete  system  of  tests, 
such  as  that  of  "VV.  J.  Keep,  cannot  be  adopted,  no  other  test  affords  so  good 
an  indication  of  the  value  of  the  metal,  as  cast  iron  with  high  tensile  strength 
is  almost  invariably  soft,  sound,  and  fluid.  In  the  following  table  seven 
analyses  by  the  author  of  samples  of  cast  iron  of  unusually  high  tensile 
strength  are  given,  together  with  the  results  obtained  at  Woolwich  in  1856, 
and  at  Wassiac.  Full  details  of  the  preparation  of  these  samples  are  given 
in  the  original  paper."  J 

,    TABLE     V. — COMPOSITION     OF     CAST     IRON     HAVING     A     HIGH    TENSILE 

STRENGTH. 


0,  ^ 

$£ 

d 

ifc 

B 

Rosebank  Irons,  1886. 

Dumbarton 
Irons. 

| 

o> 

l&* 

ll 

1 

1 

Tensile  Strength 
Pounds  per  sq.  in. 

>.... 

35,000 

40,700 

38,200 

37,200 

36,700 

37,000 

34,000 

41,200 

37,500 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent 

Per  Cent  Per  Cent 

Per  Cent 

Graphitic  Carbon 

2  59 

1  62 

2.90 

2.60 

2  31 

Combined  Carbon 

0.56 

0.36 

0.58 

0.52 

0.40 

0.32 

0.30 

0.78 

0.475 

Silicon  

1  42 

1  96 

1  29 

1  50 

1  13 

1  33 

1.34 

1  63 

1  31 

1  434 

Phosphorus  

0  39 

0  28 

0  56 

047 

0.41 

0  70 

1.09 

1.10 

0  29 

0  587 

Sulphur 

0  06 

0  03 

0  06 

0  07 

0  06 

0  05 

0  14 

0  12 

0  08 

0  074 

Manganese  .  .  . 

0.58 

0.60 

1.00 

1.00 

1.33 

0.65 

1.38 

1.29 

1.51 

1.037 

"  The  average  composition  shown  in  the  above  table  may  be  regarded  as 
typical  for  good  cast  iron  when  the  maximum  strength  is  desired,  together 
with  soundness  and  good  working  qualities.  By  increasing  the-  silicon  the 

*  Inst.  Journ.,  1891.  vol.  n.  p.  252. 
f  Inst.  C.  E.,  vol.  LXXIV.  p.  373. 
\J.  8.  C.  I.,  vol.  vii.  p.  200 


112  THE  MATERIALS  OF  CONSTRUCTION. 

metal  becomes  more  soft  and  fluid,  while  by  diminishing  the  silicon  the 
transverse  and  crushing  strength,  together  with  the  tendency  to  chill,  are 
increased." 

MALLEABLE    CAST    IRON. 

80.  The  Product  Denned. — White  cast  iron,  or  that  which  has  its  carbon 
all  in  the  combined  form,  can  be  made  "  malleable,"  or  somewhat  ductile, 
and  nearly  doubled  in  strength,  by  a  process  of  annealing,  by  which  the  carbon 
separates  from  the  iron  without  forming  a  mesh  or  matrix  in  which  the 
remaining  iron  crystals  are  imbedded  and  surrounded,  as  is  the  case  in 
ordinary  gray  cast  iron.  It  has  hitherto  commonly  been  assumed  that  this 
change  in  the  iron  was  effected  by  means  of  a  decarbonizing  agent  (oxide  of 
manganese,  or  iron  oxide  scale),  which  caused  the  carbon  to  leave  the  iron 
and  enter  into  combination  with  the  surrounding  materials,  thus  making  the 
iron  malleable.  But  Mr.  II.  B.  Stanford  has  shown,*  confirming  the  results 
of  Led  e bur — 

1.  That  only  about  10  or  20  per  cent  of  the  total  carbon  is  lost  in  the 
process;  and, 

2.  That  the  same  results  are  effected  when  the  castings  are  packed  in' 
clean  river  sand — at  least  so  far  as  the  interior  portion  of  the  cross-section  is 
concerned.     It  further  appears  from  his  investigations  that  the  carbon  of 
this  interior  portion  is  simply  changed  from  the  combined  to  the  graphitic 
form  (Ledebnr's  "  temper-carbon  ")  at  a  bright  cherry-red,  the  temperature 
not  being  high  enough  to  allow  the  excluded  carbon  to  unite  into  a  more  or 
less  continuous  mesh,  but  that  it  is  kept  in  very  minute,  separated  aggre- 
gates, thus  leaving  the  decarbonized  iron  crystals  in  immediate  contact,  as 
they  are  in  ingot  metal  (steel).     The  advantage-of  this  process  lies  in  getting 
the  final  forms  run  from  a  perfectly  fluid  iron,  at  a  comparatively  low  tem- 
perature   thus  obtaining  smooth,  full,  and  solid  castings,  which  can  then  be 
"  decarbonized  "  (chemically  speaking),  without  allowing  the  excluded  car- 

.Jwn  to  form  in  a  graphitic  matrix.  The  alternative  is  to  melt  and  cast 
direct  the  decarbonized  iron  (steel),  thus  making  what  are  known  as  steel 
castings.  This  requires  a  very  much  higher  melting  temperature,  and  thus 
the  metal  is  less  fluid,  and  it  is  apt  to  contain  gases,  or  to  generate  them  in 
the  mould  from  the  excessively  high  temperature  at  which  it  must  be  poured. 
The  effect  is  that  steel  castings  are  apt  to  be  rough  and  unsightly  on  the 
exterior  and  more  or  less  porous  on  the  interior. 

When  cast  iron  cools  slowly  from  the  melted  state  the  carbon,  which  is 
wholly  in  solution  or  in  chemical  combination,  passes  largely  into  the 
graphitic  form,  (as  shown  in  Fig.  72),  this  graphite  forming  a  complete 
matrix,  and  producing  the  dark,  leaden  appearance  of  gray  cast  iron.  In  all 
large  or  thick  castings  the  cooling  is  of  necessity  slow  (except  when  pur- 
posely chilled  at  the  surface),  and  hence  such  forms  are  not  radically  changed 

*  Trans.  Am.  Soc.  C.  E.,  vol.  XXXTV  (1895),  "Notes  on  Manufacture  and  Prop- 
erties of  Malleable  Cast  Iron,"  by  H.  B.  Stanford,  Assoc.  M.  Am.  Soc  C.  E. 


CAST  IRON. 

in  their  molecular  composition  by  the  annealing  which  constitutes  the  essen- 
tial feature  of  the  malleable  process.  Only  small  castings,  therefore,  are 
suited  to  this  process,  unless  a  very  hard  white  cast  iron  is  used,  which  does 
not  change  in  cooling  to  gray  iron  when  cast  in  thicker  or  heavier  masses. 
It  is  essential  to  the  successful  working  of  the  process  that  the  original  cast- 
ings shall  have  the  carbon  wholly,  or  nearly  so,  in  the  combined  form,  which 
then  changes  to  an  ununited  graphitic  form  when  kept  some  five  days  at  a 
bright  cherry-red  heat.  The  only  essential  characteristics  of  the  packing 
material  are,  according  to  Mr.  Stanford,  such  as  prevent  it  from  fusing  or 
adhering  to  the  castings,  or  from  caking  together  in  hard  lumps,  and  that 
it  should  not  be  too  expensive.  The  packing  serves  only  to  exclude  the  air 
and  to  hold  the  cast  forms  to  their  normal  shapes,  when  heated  and  softened, 
except  as  to  the  decarbonizing  action  of  iron-scale  packing  on  the  superficial 
portion  of  the  forms  so  treated,  as  described  below. 

81.  Method  of  Manufacture.— 7The  original  castings,  which  have  hitherto 
been  made  only  of  charcoal  pig  iron,  may  as  well  be  made  from  coke  pig 
iron,*  provided  the  sulphur  be  kept  low,  the  essential  requirement  being 
that  the  castings  shall  show  all  white  iron  (all  carbon  in  the  chemically 
combined  form).  These  are  then  packed  carefully  in  cast-iron  annealing- 
pots,  about  18  inches  by  24  inches  in  cross-section,  and  four  feet  high,  made 
in  three  sections  for  convenience  of  packing,  the  sections  fitting  together 
with  bell  and  spigot  ends.  The  castings  are  so  placed  in  the  pots  that  such 
settlement  as  occurs  in  the  oven  will  not  deform  them.  They  are  surrounded 
by  the  packing  material,  which  is  usually  a  decarbonizing  agent  for  their 
outside  portions,  but  which  serves  mainly  only  as  a  suitable  bedding  or  pack- 
ing for  large  cross-sections.  When  large  forms  are  to  be  treated,  they  are 
placed  and  covered  in  the  oven,  without  the  use  of  annealing-pots.  The  iron 
pots  waste  away  rapidly  by  oxidation,  being  able  to  serve  only  about  five 
heats,  of  five  days  each. 

The  annealing-oven  may  be  any  suitable  oven  in  which  the  temperature 
may  be  kept  nearly  constant,  and  uniform  over -its  entire  bed.  This  requires 
that  a  portion  of  the  combustion  shall  be  completed  in  the  oven  itself. 
About  five  days  are  required  to  fully  effect  the  change  in  the  condition  of 
the  carbon,  after  which  the  furnace  is  allowed  to  cool  down,  the  first  24 
hours  with  closed  doors.  The  cost  of  the  treatment  is  from  one-fourth  to 
one-half  cent  a  pound 

The  effect  of  sulphur  in  the  cast  iron  is  to  greatly  delay  the  change  in 
the  carbon  state,  thus  largely  preventing  it,  for  the  ordinary  periods  of  treat- 
ment or  requiring  a  greatly  extended  period  of  annealing  to  fully  accomplish 
it.  Thus  iron  .containing  0.04  per  cent  sulphur  will  anneal  in  three  and  one- 
half 'days,  while  iron  in  the  same  sizes  containing  0.20  per  cent  sulphur  re- 
quires about  nine  days.  Hence  if  coke  iron  is  used  the  sulphur  ingredient 
must  be  looked  to 

*  On  the  authority  of  Mr.  Stanford.     See  paper  quoted  above. 


114  THE  MATERIALS  OF  CONSTRUCTION. 

Clean,  heavy-forge  iron-scale  seems  to  be  the  best  material  to  use  for 
packing  the  castings  in  the  annealing-pots,  and  these,  being  composed  of 
iron  oxide,  having  a  strong  affinity  for  carbon,  do  extract  a  large  part  of  the 
carbon  from  the  exterior  y1^  inch  of  the  surface  of  all  castings  so  treated, 
leaving  a  bright-colored  envelope  (on  the  fracture),  containing  very  little 
graphitic  carbon.  This  skin  is  very  much  stronger  than  the  interior,  as 
shown  by  Fig.  59,  from  which  it  appears  that  the  removal  of  this  portion 
reduces  the  strength  per  square  inch  by  25  per  cent.  This  argues  that  the 
outer  skin  is  more  than  twice  as  strong  as  the  interior.*  It  is  necessary  to 
establish  this  fact  by  further  experiment  before  accepting  it  as  a  general 
truth. 

82.  Mechanical  Properties  of  Malleable  Iron. — From  what  has  been  said 
it  is  evident  that  "  malleable  iron  "  is  an  extremely  various  product,  depend- 
ing on  the  materials  used  in  the  cast,  and  also  on  the  treatment.  The 
following  table  is  taken  from  Mr.  Stanford's  paper,  which  shows  what  may 
be  accomplished  by  this  process.  The  test  specimens  were  j-f  inch  in. 
diameter,  and  were  tested  without  dressing  down  either  on  the  gripped  .endsf 
or  on  the  reduced  portion.  The  small  reduction  in  total  carbon  (which  all 
occurred  in  the  outer  portions)  and  the  change  from  combined  to  graphitic 
carbon  are  here  shown  conclusively.  The  average  tensile  strength  of  49,800 
Ibs.  per  square  inch  is  probably  about  twice  that  of  the  original  castings, 
while  the  average  elongation  of  6.6  per  cent  indicates  a  very  considerable 
ductility.  This  elongation  of  TV  inch  to  the  inch,  together  with  an  assumed 
corresponding  compression,  makes  it  apparent  that  small  sections  would 
submit  to  a  considerable  amount  of  bending  distortion  and  other  kinds  oi 
abuse  before  breaking.  In  other  words,  the  iron  is  now  twice  as  strong  to 
resist  a  static  load,  and  probably  many  hundred  times  as  strong  to  resist  the 
force  of  sJiocks  or  blows,  as  was  the  original  cast  iron. 

The  elastic  limit  in  compression  is  very  low,  but  the  compressive  defor- 
mation may  be  very  great. 

The  relative  strength  and  ductility  acquired  under  varying  periods  of 
annealing,  from  3  to  9  days,  is  shown  in  Fig.  59,  where  the  averages  of  all  the 
results  given  by  Mr.  Stanford  are  plotted,  after  being  reduced  to  a  common 
standard  of  reference.  The  few  tests  on  turned-down  specimens  are  also 
plotted,  but  these  are  too  few  to  give  either  very  accordant  or  very  trust- 
worthy results. 

In  Fig.  60  are  shown  the  results  of  tension  tests  on  malleable  cast  iron  of 
^  inch  and  T\  inch  in  thickness,  and  also  of  ^-inch  plates  which  had  been 
welded  together.  These  last  show  a  greater  strength  than  the  unwelded 
bars. 

*  Due  allowance  being  made  for  the  relative  portions  of  each. 

f  These  parts  should  have  been  dressed  iu  order  to  prevent  any  want  of  symmetry 
in  the  applied  forces,  or  forms  like  that  shown  for  cast  iron  in  Chapter  XV  could  have 
been  used.  Some  of  the  discrepancies  in  these  results  are  due  doubtless  to  the  rough, 
surfaces  in  the  grips. 


CAST  IRON. 


115 


TABLE    VI. MALLEABLE    CAST   IRON". 

CHEMICAL   COMPOSITION   (UNANNEALED   AND   ANNEALED)   AND   PHYSICAL   PROPERTIES. 


'  TESTS  OF  ANNEALED  SPECIMENS. 

fl 

o 

o 

6 

Unannealed  or 
Annealed. 

1 

|I 

•~5 

Mn. 

Si. 

P. 

S. 

Loss  of 
Carbon. 

||5 

•«'  2 

=*£ 

•~  oo  u 

c 

5 

W 

'2 

1 

llf 

!1 

!!§• 

"Pi 

ll 

& 

H 

O 

o 

O 

5  CG  Cu 

l« 

£K'Z 

go< 

K  = 

391 

j  Before  annealing 
I  After 

3.02 
2.95 

2.96 
0.15 

0.06 
2.80 

OA8 
0.19 

0.69 
0.69 

0.138 
0.140 

0.066 
0.064 

[-0.07 

55,100 

5.5 

5.2 

3 

1C8 

395 

j  Before 
\  After 

3.09 
2.98 

2.99 
0.53 

0.10 
2.45 

0.190.60 
0.190.62 

0.133 
0.130 

0.060 
0.061 

[0.11 

43,800 

6.1 

6.3 

3 

108 

400 

J  Before 
"1  After 

3.09 
2.56 

2.96 
0.31 

0.13 

2.25 

0.180.75 
0.19'0.74 

0.142 
0.142 

0.065 
0.061 

[-0.53 

44,900 

7.7 

10.3 

3 

108 

AnR     i  Before 
406    1  After 

3.07 
9.91 

2.77 
0.08 

0.30 
2.83 

0.190.65 
0.200.64 

0.163 
0.164 

0.064 
0.064 

j^O.16 

47,000 

7.2 

6.2 

3 

108 

,00  !  J  Before 
*"*  |  1  After 

3.26 
2.95 

2.65 
0.36 

0.61 
2.59 

0.17'0.69 
0.180.61 

0.156 
0.151 

0.071 
0.068 

j-0.31 

45,300 

9.1 

8.2 

3 

108 

.00     j  Before 
433    1  After 

2.85 
2.77 

2.72 

0.72 

0.13 
2.05 

0.180.74 
0.180.72 

0.161 
0.162 

0.073 
0.071 

|o.08 

64,500 

1.3 

2.8 

3 

108 

.,00    j  Before 
436    1  After 

2.88 
2.58 

2.73 

0.51 

0.15 
2.07 

0.18:0.90 

0.18'0.87 

0.196 
0.192 

0.069 
0.069 

[-0.30 

38,900 

4.3 

6.2 

3 

108 

44t-     j  Before 
'    1  After 

2.97 
2.66 

2.75 
0.31 

0.22 
2.35 

0.180.T7 
0.19,0.76 

0.148 
0.145 

0.073 
0.075 

[-0.31 

69,100 

2.6 

4.0 

2 

108 

451 

I  Before 
/  After 

3.  OS 
2.15 

2.85 
0.08 

0.23 
2.07 

0.18,0.96 
0.190.96 

0.123 
0.129 

0.033 
0.039 

[0.93 

45,400 

7  2 

8.0 

2 

108 

458 

j  Before 
1  After 

3.  OS 
2.03 

2.82 
0.28 

0.26 
1.75 

0.180.74 
0.180.71 

0.151 
0.150 

0.036 
0.037 

tl  05 

56,700 

8.4 

8  2 

2 

108 

459 

j  Before 
1  After 

3.03 
2.06 

2.81 
0.27 

0.22 
1.79 

0.19:0.70 
0.200.70 

0.195 
0.192 

0.038 
0.037 

j-0.97 

44,200 

2.1 

4.2 

3 

108 

j  Before 

3.09 

3.00 

0.09 

0.200.77 

0.127 

0.022 

'  n  oq 

n  f 

7  0 

"Iftft 

469 

I  After 

2.86 

0.32 

2.54 

0.19 

0.75 

0.129 

0.023 

J-0.23 

51,olHJ 

i  .  i 

<  .u 

lUo 

474 

J  Before 
|  After 

3.08 
2.67 

2.92 
0.09 

0.16 

2.58 

0.230.70 
0.220.70 

0.158 
0.156 

0.023 
0.023 

[-0.41 

46,600 

9.8 

8.5 

3 

108 

495 

j  Before 
1  After 

2.84 
2.58 

2.62 
0.06 

0.22 
2  52 

0.310.63 
0.320.66 

0.182 
0.178 

o.oi4j  I0  26 

0.018   f026 

48,100 

8.6 

8.7 

3 

108 

510 

j  Before 
1  After 

3.26 
3.12 

3.23 
0.53 

0.030.400.64 
2.590.400.67 

0.136    0.040 
0.1351  0  039 

[-0.14 

46,000 

5.9 

5.3 

3 

108 

Av. 

i  Before  annealing 
)  After 

3.04  2.85 
2  66  0.31 

0.190.21 
2.350.21 

0.73 
0.72 

0.154 
0.153 

0.050 
0.050 

|o.38~ 

49,810 

6.23 

6.61 

42 

108 

NOTE.— The  above  test -bars  were  all  cylindrical  in  section  and  {§  inch  in  diameter 


3  4  6  6  7  S 

FIG.  59.— Tensile  Strength  and  Per  Cent  of  Elongation  of  Cylindrical  Test-specimens  of 
Malleable  Cast  Iron  \\  in.  in  Diameter.  Figures  show  Number  of  Tests  averaged  for 
each  Point  Plotted.  (Stanford,  Tr.  Am.  Soc.  C.  E.,  vol.  xxxiv,  1895.) 


116 


THE  MATERIALS  OF  CONSTRUCTION. 


In  Plate  IV  the  plain  bar  represents  the  original  form  of  malleable  iron 
from  which  all  the  other  forms  on  the  plate  were  worked.     In  one  case  it  is 


FIG.  60.— Tension  Tests  of  Malleable  Cast  Iron.    Each  Curve  the  Mean  of  Two  or  Three 

Tests.     (Berlin  Testing  Laboratory,  1886.) 

folded  over  and  the  ends  are  welded  together,  while  in  another  it  has  been 
forged  like  wrought  iron.     All  the  other  forms  were  bent  cold. 


PLATE  IV. 


EXAMPLES  OP  COLD-BENDING,  FORGING,  AND  WELDING  OF  MALLEABLE  CAST-IKON 
SPECIMENS,  ALL  BEING  ORIGINALLY  LIKE  THE  UNDEFORMED  ONE  IN  THE 
CENTRE  OF  THE  PLATE. 

(Berlin  Testing  Laboratory  Communications,  vol.  iv,  PI.  III.) 


CHAPTER  VIII. 
WROUGHT    IRON. 

83.  Definition. — Wrought  iron  may  be  defined  as  nearly  pure  iron  inter- 
mingled with  more  or  less  slag.     As  will  appear  from  a  study  of  the  methods 
of  production  to  be  described,  the  iron  is  formed  in  a  bath  of  melted  slag 
(somewhat  as  butter  is  formed  in  churning),  and  when  it  aggregates  into  a 
pasty  mass  and  is  removed  from  the  furnace,  to  be  squeezed  and  rolled,  some 
of  this  slag  remains  intimately  associated   with  the   iron.     This  gives  to 
wrought  iron  a  fibrous  appearance  (see  Fig.  322)   not  found  in  any  other 
metal.*     In  the  most  carefully  made  iron  this  fibrous  appearance  is  uniform 
throughout  the  entire  cross-section.    It  is  not  uncommon,  however,  especially 
in  the  cheaper  grades  of  wrought  iron,  to  find  it  largely  and  coarsely  crystal- 
line.    Wrought  iron  melts  only  at  a  very  high  temperature,  and  assumes  a 
perfectly  plastic  state  through  a  considerable  range  of  temperature  below 
this  melting  heat,  in  which  condition  it  is  easily  and  perfectly  welded.     It 
is  more  or  less  ductile  when  cold,  and  will  not  harden  when  heated  and 
quenched  in  water. 

The  oldest  methods  of  production  of  wrought  iron  were  alj  direct  pro- 
cesses, obtaining  the  malleable  product  at  one  operation,  or  directly  from 
the  ore.  While  some  modern  processes  also  proceed  on  this  plan,  practically 
all  the  wrought  iron  of  to-day  is  made  from  pig  iron  and  various  kinds  of 
scrap  by  a  puddling  process. 

METHODS   OF   MANUFACTURE. 

84.  The  Puddling  Process  Briefly  Stated,  f— "  The  ordinary  puddling 
furnace,  is  a  single-bedded  reverberatory  of   simple  construction,  formed 
externally  of  cast-iron  plates,  tied  together  with  wrought-iron  rods,   and 
provided  with  suitable  openings  in  front  for  the  fire-hole  and  the  working- 
door,  and  lined  internally  with  refractory  fire-brick.     The  crown  of   the 
furnace  is  also  of  fire-brick,  and  is  open  to  the  air.     The  bottom  of  the 
furnace  is  composed  of-  three  cast-iron  plates,  which  rest  upon  an  iron  frame. 
The  grate  of  the  furnace  has  wrought-iron  fire-bars,  and  is  large  in  propor- 


*  To  develop  this  fibrous  appearance  nick  a  bar  of  wrought  iron  on  one  side  and 
bend  it  double,  and  if  possible  split  it  down  like  a  stick  of  timber.     See  Fig.  322. 

t  The  quoted  paragraphs  on  wrought  iron  have  mostly  been  taken  from  Turner's 
Metallurgy  of  Iron,  Lippincott  &  Co. ,  1895. 

117 


118 


THE  MATERIALS  OF  CONS2EUCTION. 


tion  to  the  bed  or  crucible  part  on  account  of  the  very  high  temperature 
required,  particularly  towards  the  end  of  the  process.  Each  puddling 
furnace  is  provided  with  a  separate  flue,  which  is  either  connected  to  a 
simple  rectangular  stack,  provided  with  an  iron  damper,  or  which  passes  into 
a  boiler-flue  so  as  to  economize  the  waste  heat  of  the  furnace.  A  sectional 
view  of  such  a  furnace  is  shown  in  Fig.  61. 


FIG.  61. — Plan  and  Section  of  a  Simple  Reverberutory  Furnace. 


"  Two  men  are  employed  at  each  furnace,  and  are  called  the  '  puddler* 
and  the  '  under-hand '  respectively.  The  work  is  very  laborious,  while  it 
entails  no  little  skill  if  good  results  are  to  be  obtained.  Usually  six  heats 
are  worked  in  a  turn  of  twelve  hours,  but  exceptionally  seven  heats  are 
obtained. 

"  The  furnace  is  first  charged  with  a  sufficiency  of  fluxing  cinder  or 
*  hammer  slag '  (oxide  of  iron)  which  has  been  squeezed  out  under  the 
hammer  from  previous  balls,  and  there  is  then  introduced  about  500  Ibs.  of 
good  gray  forge-iron.  The  door  is  closed  and  the  charge  is  then  heated  to 
melt  the  iron,  and  the  most  favorable  results  are  obtained  when  the  iron 
and  the  cinder,  charged  as  above  described,  become  pasty,  and  melt  down 
together.  When  the  iron  has  thoroughly  melted  down  and  has  become 
fluid,  it  is  carefully  watched  until  it  has  *  cleared,'  and  until  a  number  of 
small  blue  jets  of  flame  issue  from  the  surface  of  the  liquid.  The  damper  is 
now  '  put  down,'  or  closed,  so  as  to  fill  the  furnace  witfo  a  reducing  (non- 
oxidizing)  atmosphere,  and  to  lower  the  temperature  somewhat.  In  a  short 
time  the  jets  of  blue  flame  almost  cease,  and  the  mixture  of  iron  and  cinder 
rises  in  the  furnace  to  a  height  of  some  8  or  10  inches,  and  during  this  stage 
constant  stirring  or  '  rabbling '  is  necessary  to  prevent  the  iron  settling  on 


WROUGHT  IRON.  119 

the  bottom  of  the  furnace,  and  to  assist  the  decarburization  by  bringing  the 
(carburized)  iron  and  cinder  (iron  oxide)  into  uniform  and  intimate  contact. 
The  whole  mass  should  now  be  in  motion,  and  bubbles  of  gas  should  rise  and 
burn  with  a  blue  flame,  tinged  more  or  less  with  yellow,  at  the  surface. 
When  the  '  boil '  is  thus  in  full  progress,  or  '  well  on,'  the  damper  may  be 
raised  somewhat,  and  the  iron  will  soon  be  observed  to  '  come  to  nature  '  or 
to  separate  from  the  cinder.  The  first  sign  of  this  is  the  appearance  of 
small  bright  spots  on  the  surface  of  the  cinder,  which  alternately  appear  and 
disappear.  The  cinder  now  gradually  sinks,  and  leaves  the  iron  as  an  irreg- 
ular mass,  not  unlike  the  small  globules  or  grains  of  butter  produced  by  the 
churn;  and  as  in  good  butter-making  so  in  good  puddling,  the  grains  should 
be  small  and  uniform  throughout  the  mass.  The  temperature  should  now 
be  raised  to  the  highest  point  so  that  the  iron  may  be  at  a  welding  heat;  the 
puddler  after  first  lifting  the  metal  and  turning  it  over,  by  inserting  a  bar 
underneath  in  order  to  prevent  the  bottom  becoming  colder  than  the  top, 
and  breaking  it  up,  proceeds  to  collect  it  into  balls,  which  are  taken  to  the 
hammer." 

-9^5.  Oxidation  in  Puddling. — "  The  following  remarks  on  the  oxidation 
of  cast  iron  under  different  conditions,  will  explain  the  differences  between 
the  old  and  newer  processes  of  puddling. 

"  It  is  usual  to  speak  of  atmospheric  air  as  oxidizing  and  removing  the 
impurities  present  in  cast  iron,  but  if  a  globule  of  cast  iron  be  melted  in  the 
air,  and  then  exposed  to  a  blast  of  air  or  oxygen,  it  will  be  observed  that  the 
impurities  are  not  the  only  substances  that  are  oxidized.  It  is  true  that 
under  very  special  conditions  either  the  carbon  or  the  silicon  may  be 
separately  oxidized.  But  on  performing  the  experiment  above  indicated  it 
will  be  found  that  the  iron  itself  is  oxidized  in  about  the  same,  relative  pro- 
portion as  the  other  elements,  and  the  result  is  that  practically  a  layer  of 
impure  magnetic  oxide  of  iron  is  formed  outside  the  globule,  while  the  por- 
tion of  metal  that  is  left  is  of  nearly  the  same  composition  as  the  original 
iron.  If  the  cinder  be  allowed  to  run  away  as  rapidly  as  it  is  formed,  ulti- 
mately the  whole  of  the  iron  would  be  converted  into  magnetic  oxide,  and 
the  last  particles  of  cast  iron  so  removed  would  have  nearly  the  same  com- 
position as  the  original  metal.  In  this  case  oxidation  has  taken  place,  but 
no  purification  has  resulted. 

"  If,  now,  the  same  experiment  be  tried,  but  the  fluid  oxide  be  allowed 
to  remain,  and  to  cover  the  fused  metal,  the  oxidation  of  the  iron  will  pro- 
ceed very  little  further;  a  reducing  action  will  then  be  commenced  whereby 
the  silicon,  carbon,  and  other  easily  oxidizable  elements  will  be  removed, 
but  at  the  same  time  a  corresponding  weight  of  iron  will  be  returned  to  the 
globule  from  the  surrounding  slag. 

"  If,  thirdly,  a  globule  of  cast  iron  be  covered  with  magnetic  oxide  of 
iron  to  protect  it  from  the  air  and  to  supply  the  necessary  cinder,  and  it  be 
then  strongly  heated,  it  will  be  found  that  the  globule  has  not  lost  in  weight, 
but  has  become  distinctly  heavier  during  the  process.  It  is  scarcely  neces- 


120  TEE  MATERIALS  OF  CONSTRUCTION. 

sary  to  say  that  the  waste  which  takes  place  daring  reheating  or  remelting, 
corresponds  to  the  first  condition  above  given.  The  oxide  runs  away  as  it  is 
formed,  and  this  is  an  example  of  waste  of  iron  pure  and  simple.  The  only 
redeeming  feature  is  that  sometimes  the  oxide  produced  may  be  of  value  for 
other  purposes.  The  early  open-hearth  processes  for  producing  wrought 
iron  in  fineries,  and  the  original  method  of  puddling,  resemble  the  second 
case,  for  part  of  the  iron  is  wasted  to  produce  the  cinder  needed  to  remove 
the  impurities  from  the  remainder  of  the  metal.  The  larger  the  proportion 
of  these  impurities  the  greater  will  be  the  loss  of  iron  necessary  to  make  the 
required  cinder,  and  for  this  reason  a  comparatively  pure  iron  is  needed,  in 
order  to  obtain  the  least  waste,  while  at  best  the  waste  is  comparatively 
great.  A  deficiency  of  fluid  cinder  in  the  early  stages  of  ordinary  puddling, 
or  pig  '  boiling,'  has  an  exactly  similar  effect,  and  leads  to  waste  for  the 
same  reasons, 

"  In  the  modern  method  of  working,  on  the  other  hand,  the  object  is  to 
imitate  the  conditions  of  the  third  case  previously  supposed.  Oxide  of  iron 
can  be  bought  much  more  cheaply  than  it  can  be  made  from  pig  iron,  and 
besides  the  oxidation  of  pig  iron  requires  the  expenditure  of  time  and  fuel. 
Oxide  of  iron  is,  therefore,  supplied  in  its  cheapest  and  most  readily  available 
form,  and  as  much  of  this  oxide  as  possible  is  reduced  and  converted  into 
wrought  iron.  To  do  this  it  is  necessary  that  the  iron  and  fluid  oxide 
should  be  brought  into  actual  and  frequent  contact,  and  so  perfect  fluidity 
and  constant  rabbling  are  needed.  There  is,  of  course,  a  practical  limit  to 
the  amount  of  carbon  which  can  be  present,  due  to  the  fact  that  cast  iron 
cannot  take  up  more  than  a  certain  amount,  say  4  per  cent,  of  this  element. 
There  is  also  a  practical  limit  in  the  case  of  both  silicon  and  phosphorus; 
the  first  being  regulated  by  the  increased  consumption  of  time  and  fettling 
with  excess  of  silicon,  and  the  second  being  determined  by  the  inferior 
quality  of  iron  produced,  with  large  proportions  of  phosphorus.  But  within 
these  practicable  limits  it  is  advantageous  to  reduce  as  much  of  the  oxides 
of  iron  supplied  as  possible." 

86.  Details  of  the  Puddling  Process. — "  The  working  heat  of  puddled 
iron  may  be  conveniently  divided  into  four  stages,  which  will  be  separately 
described,  namely: 

"  (1)  Melting-down  stage,  lasting  about  half  an  hour,  by  the  end  of 
which  most  of  the  silicon  and  manganese  and  a  considerable  proportion  of 
phosphorus  have  been  removed. 

"  (2)  Quiet  fusion  or  '  clearing  '  stage,  lasting  about  ten  minutes, 
during  which  the  rest  of  the  silicon  and  manganese  and  a  further  quantity 
of  phosphorus  are  removed. 

"  (3)  The  boil,  which  lasts  nearly  half  an  hour,  during  which  the  greater 
part  of  the  carbon  is  eliminated,  together  with  a  further  quantity  of  phos- 
phorus. 

"  (4)  Balling-up  stage,  which  occupies  some  twenty  minutes,  and  by 


WROUGHT  IRON.  121 

which  time  the  purification,  except  as  regards  the  removal  of  slag,  has  prac- 
tically ceased. 

"  1.  The  furnace  having  been  suitably  prepared,  and  hot  from  a  previous 
heat,  the  pig  iron  is  charged  as  before  described ;  the  door  is  then  closed,  and 
the  working  opening  in  the  bottom  of  the  door  covered  with  an  iron  plate 
and  rendered  as  far  as  possible  air-tight  by  means  of  a  little  fine  cinder 
thrown  with  the  shovel.  The  fire  is  also  made  up,  and  heating  proceeds  for 
some  twenty  minutes,  by  which  time  the  top  of  the  pig  iron  is  red-hot,  and 
the  flux  begins  to  soften.  The  pigs  are  now  turned  so  as  to  heat  them  more 
uniformly  and  the  door  is  again  closed ;  in  a  few  minutes  the  iron  begins  to 
melt,  and  if  carefully  watched  may  be  seen  to  trickle  down  into  the  cinder 
in  drops.  The  workman  now  introduces  an  iron  rod,  stirs  up  the  mass,  and 
brings  up  any  pieces  of  iron  which  have  not  completely  melted,  and  which 
might  otherwise  remain  covered  and  take  longer  to  melt.  When  the  whole 
is  thoroughly  fluid  and  well  mixed  the  melting-down  stage  is  finished. 

"  2.  One  of  the  workmen,  generally  the  under-hand,  now  introduces  a 
bar  which  is  bent  at  the  end  at  right  angles,  and  so  acts  as  a  scraper  or 
stirrer,  and  the  whole  charge  is  well  stirred  and  exposed  to  the  action  of  the 
fettling  and  cinder,  and  also  to  some  extent  to  the  oxidizing  influence  of  the 
air.  The  temperature  is  maintained  as  high  as  possible  during  this  stage. 

"  The  iron  is  thus  thoroughly  '  cleared '  or  purified  from  silicon,  the 
point  at  which  clearing  is  completed  being  judged  by  the  appearance  of  the 
charge,  and  upon  the  skill  of  the  workman  at  this  stage  much  of  the  subse- 
quent  success  depends. 

"3.  When  the  metal  has  cleared,  and  is  in  a  state  of  tranquil  fusion,  the 
next  point  is  to  bring  on  the  '  boil.'  The  puddler,  therefore,  diminishes  the 
draught,  or  '  puts  his  damper  down,'  so  as  to  fill  the  furnace  with  a  smoky 
flame  and  lower  the  temperature.  In  some  cases  also  the  door  is  opened  and 
water  thrown  in  at  this  stage,  as  this  promotes  rapid  cooling  and  supplies 
oxygen  at  the  same  time.  The  (carbonized)  metal  being  thus  somewhat 
thickened,  and  being  vigorously  stirred  "during  the  whole  time,  becomes 
intimately  mixed  with  the  (iron  oxide)  cinder;  the  carbon  is  thus  oxidized, 
producing  carbon  monoxide,  which  burns  in  blue  flames  as  the  bubbles  of  gas 
rise  and^urst.  These  flames  are  sometimes  called  '  sulphur  '  or  '  puddler's 
candles,'  on  account  of  their  pale  blue  color.  The  charge  thus  swells  up  and 
rises  some  six  inches  in  the  furnace  (like  boiling  molasses),  and  as  the  heat 
increases  and  the  damper  is  opened  somewhat,  a  quantity  of  red-hot  slag 
flows  over  the  fire-plate  (at  the  door)  into  a  cast-iron  slag-wagon  placed 
ready  to  receive  it.  The  violence  of  the  action  now  gradually  diminishes, 
the  iron  '  comes  to  nature, '  and  the  charge  settles  in  the  furnace ;  the  less 
fusible  wrought  iron  is  in  the  form  of  a  porous  cake,  and  the  residue  of  slag 
collects  chiefly  underneath. 

"  4.  In  the  fourth,  and  last,  stage  the  puddler  has  to  manipulate  the 
iron  into  convenient  forms  for  subsequent  treatment.  For  this  purpose  the 


122  THE  MATERIALS  OF  CONSTRUCTION. 

cake  of  metal  is  broken  up  by  inserting  a  bar  underneath,  and  is  worked  at 
a  welding  heat  into  one  uniform  mass  or  ball.  This  is  now  divided  into 
about  six  balls,  of  approximately  equal  size,  each  of  which  weighs  about  80 
Ibs.,  and  these  are  in  turn  withdrawn  from  the  furnace  and  taken  to  the. 
hammer,  where  the  slag  is  to  a  great  extent  expelled,  and  a  bloom  of  iron  is 
obtained.  This  is  rolled,  without  reheating,  into  'puddled  bar,'  which  is 
the  name  given  to  the  crude  wrought  iron  produced  as  above  described." 

87.  Production  of  Muck  Bars. — "  The  balls  of  crude  wrought  iron,  hav- 
ing been  produced  in  the  puddling-f  urnace  as  before  described,  have  now  to 
be  compressed  to  expel  the  slag  and  render  the  material  more  uniform  in 
character;  they  are  afterwards  rolled  into  bars,  which  receive  the  name  of 
*  muck  bars.'  For  compressing  the  iron  various  forms  of  hammers  or 
squeezers  are  used,  while  for  the  production  of  bars,  grooved  rolls,  as  intro- 
duced by  Cort  in  1783,  are  generally  employed,  though  in  a  few  exceptional 
cases,  where  water-power  is  available,  bars  are  still  produced  by  the  hammer 
or  '  battery,'  as  in  ancient  times. 

"  Various  forms  of  squeezers  have  been  introduced  from  time  to  time, 
chiefly  with  the  object  of  preventing  the  jar  or  shock  due  to  the  action  of  the 
hammer,  though  such  appliances  have  not  met  with  very  general  application. 
The  more  usual  forms  may  be  conveniently  divided  into  two  classes : 

"  (1)  Those  in  which  compression  is  produced  by  means  of  a  lever,  as  in 
the  '  alligator  '  or  '  crocodile  '  squeezers,  which  are  so  called  by  the  workmen 
from  the  resemblance  between  the  motion  of  this  class  of  squeezer  and  that 
of  the  mouths  of  the  animals  above  mentioned. 

"  (2)  Those  in  which  a  revolving  cam  is  employed. 

"  Though  squeezers  appear  at  first  sight  to  have  many  advantages  over 
hammers,  particularly  on  account  of  their  even  and  quiet  action,  they  do  not 
seem  to  have  grown  in  general  favor  in  recent  years,  it  being  stated  that  the 
iron  worked  in  squeezers  is  less  uniform  in  character,  and  that  the  slag  is 
not  so  completely  expelled  by  squeezers  as  with  hammers. 

"  Steam  hammers  are  used  for  shingling  puddled  balls  in  almost  all 
modern  works,  and  are  now  always  double-acting.  The  hammer-block  in 
this  instance  weighs  about  ten  tons,  and  is  heavier  than  is  generally  employed 
in  forges,  though  lighter  than  is  usual  for  manipulating  large  masse^f  steel. 
Forge-hammers  seldom  exceed  three  tons  in  weight,  while  steam-hammers 
for  forgings  of  the  largest  size  weigh  50  tons  and  upwards. 

"  The  iron,  having  been  thus  compressed  and  consolidated  by  some  form 
of  hammer  or  squeezer,  and  a  considerable  portion  of  the  slag  expelled,  is 
now  taken  while  still  hot  to  the  puddle-rolls,  where  it  is  converted  into  bars. 
The  bars  are  allowed  to  cool,  and  are  afterwards  cut  np  with  shears  into 
suitable  lengths;  these  are  then  made  into  bundles,  or  '  piles,'  of  the  required 
weight  and  size.  When  a  specially  smooth  surface  is  required,  as  in  the 
production  of  sheet  iron,  it  is  usual  to  make  the  top  and  bottom  of  each  pile 
of  '  scrap  bars  ' ;  these  are  made  by  reheating  the  crop  ends  of  finished  bars 
or  other  good  wrought-iron  scrap,  and  are  therefore  more  uniform  in  char- 


WROUGHT  IRON.  123 

acter,  and  possess  a  smoother  and  cleaner  surface  than  ordinary  puddled 
iron. ' ' 

88.  Reheating  the  Muck  Bars. — "  The  puddled  iron  having  been  pre- 
pared as  before  described,  is  now  taken  from  the  forge  to  the  other  part  of 
the  works,  which  is  known  as  the  '  mill.'     This  is  usually  covered  with  a 
tolerably  lofty  roof,  but  is  open  at  the  sides;  it  contains  reverberatory  furnaces 
for  heating  the  piles  of  puddled  iron,  and  also  rolls  of  various  sizes,  with  the 
necessary  engine  and  connections  required  for  producing  the  various  '  sec- 
tions '  of  finished  iron.     A  steam-hammer  is  also  provided  if  forgings  are 
produced,  but  otherwise  this  is  not  required. 

"  The  temperature  employed  in  mill-furnaces  is  a  white  heat,  and  suffi- 
ciently high  to  cause  the  metal  to  weld  together  when  it  is  passed  through 
the  rolls,  to  which  it  is  taken  from  the  furnace." 

89.  Rolls. — "  The  rolls  used  in  iron- works  are  classified  according  to 
their  shape  and  the  method  adopted  in  their  production.     They  are  gener- 
ally made  from  a  strong  close-grained  cast  iron,  usually  that  obtained  from  a 
blast-furnace,  in  which  cold  blast  is  employed.     Occasionally  steel  rolls  are 
used,  and  these  appear  to  be  somewhat  growing  in  favor  in  recent  years. 

"  Rolls  may  be  classified  according  to  their  shape  into — 

"  (1)  Flat  or  plain  rolls,  which  are  used  for  rolling  sheets  or  plates. 

"  (2)  Grooved  rolls,  which  are  required  for  the  production  of  bars,  rods, 
angle  and  channel  iron. 

"  According  to  their  method  of  production  rolls  are  classified  as — 

"  (1)  Grain  rolls,  which  are  produced  in  moulds  of  green  or  dry  sand, 
and  in  which  the  surface  of  the  roll  after  turning  down  shows  the  ordinary 
grain  of  the  cast  iron  from  which  it  is  made.  These  are  used  for  all  rough- 
ing purposes  and  for  sections,  and  in  other  cases  if  the  metal  is  finished  hot. 

"  (2)  Chilled  rolls,  which  are  produced  in  cast-iron  moulds  or  chills. 
TKey,  therefore,  have  a  hard  white  surface  of  chilled  iron,  which  varies  in 
thickness  from  about  i  to  f  of  an  inch,  according  to  the  size  of  the  casting 
and  the  class  of  work  for  which  it  is  intended.  Rolls  of  this  kind  are  more 
costly,  and  are  employed  for  the  production  of  sheets,  plates,  or  strip,  or 
in  other  cases  where  specially  fine  surfaces  are  required." 

Small  rolls  tend  more^to  elongate  than  to  spread  the  materials,  while 
large  rolls  tend  both  to  elongate  and  to  spread  the  metal. 

90.  Effect  of  Repeated  Reheating  of  Iron. — "As  it  is  well  recognized 
that  puddled  iron  is  much  improved  in  quality  by  being  cut  up,  piled, 
reheated,  and  rolled  or  hammered,  and  that  the  iron  is  further  improved 
by  repeating  the  operation,  it  might  be  assumed  that  by  continuing  this  pro- 
cess the  properties  of  the  metal  might  be  again  and  again  further  improved. 
In  practice,  however,  this  is  not  found  to  be  the  case,  and  it  is  only  in 
special  cases  that  it  is  advantageous  to  reheat  puddled  iron  more  than  twice. 
It  has  been  shown  by  experiments,  in  which  puddled  bar  was  reheated  and 
rolled  as  many  as  twelve  times,  that  after  about  six  workings  the  metal  began 
to  seriously  deteriorate,  and  even  in  the  earlier  workings,  after  the  third  no 


124  THE  MATERIALS  OF  CONSTRUCTION. 

corresponding  advantage  was  obtained  for  the  fuel  and  labor  expended  and 
the  waste  incurred.  The  results  obtained  were  as  follows  ( Useful  Metals, 
p.  318): 

Tensile  Strength  in 
Pounds  per  Square  Inch. 

Original  puddled  bar 43,900 

2d  working 52,860 

3d        " 59,580 

4th      "         59,580 

5th      "         57,340 

6th      "         61,820 

7th      " 59,580 

8th      «         57,340 

9th      "         57,340 

10th      "         54,100 

llth      « 51,970 

12th      "         •. . . .   43,900 

"If  it  be  assumed  that  the  result  in  the  fifth  heating  was  accidentally 
low,  it  will  be  seen  that  all  the  other  tests  follow  in  a  regular  succession,  the 
maximum  tensile  strength  being  obtained  with  the  sixth  working.  Probably 
with  iron  of  different  composition  or  character  the  maximum  would  be 
reached  at  a  different  point,  but  in  all  cases  the  gradual  original  improve- 
ment and  subsequent  deterioration  would  be  observed.  When  the  metal 
passes  into  the  bands  of  the  smith  it  is  found  that  if  it  has  been  worked 
during  its  previous  preparation  so  as  to  bring  it  to  its  best  condition,  it  has  a 
tendency  to  '  go  back  '  in  forging;  while,  on  the  other  hand,  if  the  iron  has 
not  been  unduly  'worked,  it  improves  when  properly  smithed.  For  this 
reason  also  it  is  not  advantageous  to  often  reheat  and  work  iron  during  the 
process  of  manufacture,  and  '  best,'  '  best  best,'  or  '  treble  best '  irons  are 
obtained,  not  by  frequent  heatings,  as  is  sometimes  stated,  but  by  the  careful 
selection  of  all  the  materials  employed,  and  by  systematic  and  frequent  tests 
of  the  iron  during  the  various  stages  of  manufacture." 

91.  Sections  of  Finished  Iron. — "  The  shape  into  which  finished  iron  is 
rolled  varies  according  to  the  purposes  f<;^  which  it  is  designed,  the  chief 
divisions  being  plates,  sheets,  strips,  bars,  angle-irons,  and  rails,  the  last  being 
relatively  of  much  less  importance  than  formerly.  Among  the  more  usual 
shapes  or  '  sections  '  may  be  mentioned  the  following :  bars,  including  round, 
half-round,  square,  flat,  round-edged  fiats,  oval,  octagon,,  together  with 
levelled  and  bulb  iron,  and  rods;  tee  (or  T-shaped)  iron,  tee^with  round  top 
or  edges;  angle-  (or  L-shaped)  iron,  angle-iron  with  unequal  sides  or  round 
back;  channel-iron,  I  iron,  Z  iron;  rails,  including  single-headed,  double- 
headed,  and  flange;  and  horseshoe-iron,  which  is  rolled  sftigle-grooved, 
double-grooved,  or  concave.  Numerous  other  forms  are  also  Required  from 
time  to  time  for  various  purposes;  so  that  the  number  of  rolls  which  have  to 


WROUGHT  IRON.  125 

be  kept  in  stock  at  a  large  works  with  a  general  trade  is  very  great,  not 
unfrequently  amounting  to  hundreds.  As  each  pair  of  rolls  is  generally  only 
capable  of  finishing  one  section  of  iron,  the  cost  of  the  supply  and  main- 
tenance of  rolls  forms  a  considerable  item  of  the  expenditure  of  an  iron- 
works." 

92.  Imperfections  in  Finished  Iron. — "  The  three  chief  varieties  of 
imperfection  in  the  appearance  of  finished  iron  are  rough  edges,  spilly 
places,  and  blisters. 

"  (a)  Rougli  edges,  when  not  due  to  imperfections  in  the  rolls  or  to  care- 
less working,  are  a  sign  of  red-shortness,  and  are  particularly  noticeable  in  flat 
bars  or  strips.  Red -shortness  may  be  due  to  an  excess  of  carbon,  or  to  the 
presence  of  sulphur,  particularly  if  copper  is  also  present.  Usually,  how- 
ever, if  iron  has  been  properly  puddled,  practically  the  whole  of  the  sulphur 
is  eliminated,  and  the  red-short  condition  is  due  to  the  '  dryness  '  of  the  iron. 
Iron  is  said  to  be  dry  when.it  is  deficient  in  fusible  or  welding  cinder,  which 
may  be  readily  squeezed  out  from  between  the  particles  when  the  iron  is 
worked,  and  so  enable  clean  surfaces  to  be  brought  together  to  form  a  good 
weld.  A  thick  dry  cinder,  on  the  other  hand,  leads  to  red-shortness,  and  a 
piece  of  brick  or  other  foreign  matter  which  crushes  up  in  the  rolls  to  form 
a,  dry  powder  acts  in  the  same  manner. 

"  (^)  Spilly  places  are  spongy  or  irregularly  spotted  parts  which  are  not 
unfrequently  noticed  in  sheets,  and  which  are  occasionally  met  with  in  all 
kinds  of  wrought  iron.  They  are  generally  due  to  imperfect  puddling, 
whereby  one  part  of  the  iron,  when  '  coming  to  nature,'  has  been  oxidized 
more  than  another.  If  the  heat  has  been  thoroughly  well  worked  and  the 
iron  uniformly  mixed,  spilly  places  are  seldom  observed. 

"  (c)  Blisters  are  not  unfrequently  met  with  in  sheets,  and  'lead  to  con- 
|siderable  loss  and  inconvenience.  They  are  much  less  common  in  steel  sheets 
than  in  iron,  and  some  experiments  conducted  in  1803  led  the  author  to 
ittribute  the  formation  of  blisters  to  a  reaction  between  carbon  and  oxide  of 
jiron  in  wrought  iron  of  inferior  quality.  This  view  is  in  accordance  with  the 
experiments  of  A.  Friedmann,  who  collected  and  analyzed  the  gas  contained 
in  a  number  of  blisters.  This  gas  was  found  to  contain  over  70  per  cent  of 
carbon  monoxide,  the  remainder  being  chiefly  carbon  dioxide,  with  some 
nitrogen  and  hydrogen.  Inside  th ;  blisters  a  quantity  of  scaly  matter  is 
found,  which"  Friedmann  states  to  consist  of  about  two  thirds  silica  and 
nearly  one  third  iron  aluminate  (FeAlOJ,  together  with  small  quantities  of 
other  oxides."* 
| 

MECHANICAL   PROPERTIES   OF   WROUGHT   IRON. 

L93.   Crystalline  Fracture. — As  explained  in  Art.  84,  the  fibrous  appear- 
ce  of  wrought  iron  when  nicked  and  bent  with  a  splitting  action,  similar 
o  that  of  a  piece  of  timber  treated  in  like  manner,  is  due  to  the  presence  of 

*  Inst.  Journ.,  188o,  vol    IT.  p.  645, 


126  THE  MATERIALS  OF  CONSTRUCTION. 

the  foreign  matter  which  formed  the  slag  or  bath  from  which  the  puddled 
ball  was  taken.  Ordinarily  when  wrought  iron  is  broken  in  tension  in  a  test- 
ing-machine the  fracture  appears  to  be  wholly  fibrous,  somewhat  like  that 
of  soft  steel,  but  with  a  darker  and  more  ragged  appearance.  If  a  wrought- 
iron  bar  be  nicked  and  broken  by  bending,  it  will  usually  show  a  fibrous 
appearance,  whereas  steel  so  treated  will  always  show  a  crystalline  fracture. 
Occasionally,  however,  a  part  of  all  of  the  fracture  of  a  test  specimen  of 
wrought  iron,  whether  broken  in  tension  or  by  nicking  and  cross-bending, 
will  have  a  coarsely  crystalline  fracture.  It  is  very  common,  also,  to  find 
such  a  fracture  when  wrought  iron  breaks  in  service,  as  in  the  case  of  car  and 
wagon  axles,  steam-engine  cranks  and  pins,  etc.  In  such  cases  as  these  it 
has  been  common  to  ascribe  the  failure  to  the  crystallized  condition  of  the 
iron  and  to  assume  that  the  iron  had  changed  to  this  condition  in  service. 
This  is  called  the  theory  of  the  cold  crystallization  of  wrought  iron.  Those 
who  believe  in  it  usually  ascribe  the  change  to  a  vibratory  action.  Whether 
or  not  wrought  iron  ever  does  crystallize  in  service  in  this  or  in  any  other 
manner  has  been  a  disputed  question  for  the  last  half-century.  It  has, 
however,  remained  a  theory  the  truth  of  which  has  never  been  established 
by  actual  experiment,  and  it  is  now  one  which  seems  to  have  no  scientific 
adherents.  It  has,  however,  become  so  thoroughly  fixed  in  the  minds  of  the 
less  educated  users  of  iron  and  steel  that  it  is  met  with  on  every  hand,  and; 
this  action  is  stated  to  be  a  fact  with  the  most  positive  assurance  by  nearly 
all  mechanics  and  is  commonly  believed  by  the  public  generally.  The  views  • 
of  the  author  of  this  work  on  this  subject  may  be  summarized  as  follows: 

I.  The  normal  molecular  arrangement  of  wrought  iron  is  crystalline,  but 
the  thorough  admixture  of  the  inert  slag  in  a  well-worked  product  prevents  j 
these  crystals  from  forming  in  visible  sizes.     The  ordinary  fibrous  fracture,  j 
therefore,  exhibits  rather  a  lateral  view  of  these  finely  crystallized  threads, 
thus  causing  this  to  present  a  fibrous  appearance. 

II.  When  any  portion  of  the  puddled  ball  as  removed  from  the  furnact 
is  not  intermixed  with  foreign  matter,  as  may  be  the  case  from  overheating  j 
and  melting  of  some  portion  of  the  puddled  ball,  or  from  the  inclusion  in  tin 
mass  of  some  unreduced  melted  cast  iron,  these  portions  being  really  of  th« 
nature  of  ingot  metal  or  steel,  rather  than  of  wrought  iron,   then  thesi 
masses  of  iron,  free  from  foreign  matter,  when  somewhat  cooled  and  rolleo 
into  a  bar,  will  form  in  that  bar  a  part  of  the  cross-section  which  will  be  abl< 
to  crystallize  on  a  slow  cooling  in  large-sized  crystals,  so  as  to  be  clearly  visibl 
to  the  naked  eye.     When  such  melted  portions  are  due  to  overheating  o 
the  puddled  ball  the  iron  is  said  to  be  burnt,  but  a  too-rapid  hurrying  of  th 
boiling  process  under  a  low  heat  will  also  enable  some  of  the  unreduced  cas 
iron  to  be  removed  from  the  furnace  in  this  way  with  a  similar  result. 

III.  With  the  ordinary  and  more  inferior  grades  of  wrought  iron  now  o 
the  American  market,  it  is  very  common  to  find  large  portions  of  the  c 
section  of  test-bars  showing  a  crystalline  appearance,  even  for  tension- 
specimens  of  standard  form.     Much  more,  therefore,  are  such  irons  likely 


WROUGHT  IRON.  127 

have  this  appearance  when  nicked  and  broken  across,  or  when  nicked  and 
pulled  in  tension. 

IV.  All  wrought  iron  when  broken  with  extreme  suddenness  will  show  a 
crystalline  fracture.     This  is  because  time  is  not  given  for  the  drawing  out 
of  the  section,  rupture  occurring  directly  across  the  fibres,  so  that  the  frac- 
ture shows  only  the  end  view  of  the  same. 

V.  When  a  bar  is  nicked  with  a  sharp  chisel,  or  grooved  in  a  lathe  with 
a  sharp-pointed  tool,  and  broken  across,  rupture  begins  at  one  side  without 
any  elongation  of  the  fibres,  and  extends  from  fibre  to  fibre  across  the  section 
in  such  a  way  as  to  produce  a  result  similar  to  that  caused  by  an  instan- 
taneous rupture  cited  in  IV.     In  this  way  wrought  iron  will  often  show  a 
crystalline  or   granular  'fracture,  when  under  the  ordinary  tensile  test  it 
would    be  wholly  fibrous.     All   steel  or  ingot   metal  will   always  show  a 
crystalline  fracture  when  treated  in  this  manner,  although  for  all  the  soft 
and  medium  grades  of  steel  the  fracture  is  always  fibrous  or  silky  when 
broken  in  tension,  with  the  usual  accompanying  elongation  and  contraction. 

VI.  Much  of  the  so-called  wrought  iron  on  the  market  to-day  consists 
simply  of  rolled  fagots  of  "  scrap-iron,"  a  large  portion  of  which  is  really 
scrap-steel.     As  these  are  heated  only  to  a  welding  heat,  and  then  rolled  into 
merchant  bar,  there  is  no  real  mixing  of  the  metals,  and  the  several  com- 
ponents form  so  many  separate  portions  of  the  cross-section  of  the  final  rolled 
forms.     The  crystallized  steely  areas  found  in  the  fractures  of  most  wrought 
irons  of  the  common  grades  to-day  can  be  largely  traced  to  this  source. 
Wrought-iron  railway-axles  and  other  large  forms  are  usually  made  up  in 
this  way. 

VII.  When   wrought  iron   breaks  in  service,   therefore,   and   shows   a 
coarsely   crystalline   fracture,    it   does   not   prove   that    crystallization   has 
occurred  in  service.     It  proves  only  that    this  iron  had  such  a  structure 
originally.     If,  however,  the  rupture  occurs  in  practice  in  a  suddenly  con- 
tracted area,  as  in  a  screw-thread  or  in  a  sharp  angle,  or  if  it  has  been  pro- 
duced with  extreme  suddenness,  as  in  case  of  an  explosion  or  shock  of  any 
kind,  if  the  appearance  of  the  fracture  is  finely  crystalline  or  granular,  this 
appearance  may  be  wholly  due  to  the  method  of  failure.     This  is  shown  by 
the  fact  that  if  a  specimen  be  cut  from  the  adjoining  metal  and  tested  in 
tension  with  the  standard  form  of  specimen,  it  might  show  a  wholly  fibrous 
fracture.     In  such  cases,  therefore,  the  crystalline  appearance  of  the  fracture 
is  due  to  the  particular  conditions  as  to  shape  of  specimen  and  suddenness  of 
rupture  and  not  to  any  molecular  change  which  has  taken  place  in  the  iron.* 


*  From  the  Report  of  U.  S.  Watertown  Arsenal  Tests  of  Metals  for  1890,  in  which  are 
recorded  many  tests  of  specimens  cut  from  the  journals  of  old  railway-axles,  the  follow- 
ing note  is  taken  : 

"Axles  have  been  examined  which  have  had  long-continued  service,  the  journals  of 
which  showed  incipient  cracks,  indicating  that  rupture  had  begun  and  that  further  use 
must  result  in  complete  rupture.  It  is  a  remarkable  fact  that  the  tests  of  the  metal  of 
these  journals  near  these  cracks  showed  no  loss  of  strength  or  ductility.  No  indications 


128  THE  MATERIALS  OF  CONSTRUCTION. 

94.  The  Welding  of  Wrought  Iron. — It  is  a  peculiar  property  of  wrought 
iron  that  it  remains  in  a  plastic  condition  throughout  a  considerable  range  of 
temperature.  If  two  pieces  of  wrought  iron  could  be  reduced  to  this  plastic 
state  (a  white  heat)  with  perfectly  clean  surfaces,  and  pressed  together 
firmly  and  allowed  to  cool,  the  union  would  be  so  perfect  as  to  be  practically 
as  strong  as  any  other  portion  of  the  material.  The  great  difficulty  in  suc- 
cessful welding  lies  in  the  fact  that  when  the  iron  is  heated  in  the  presence 
of  oxygen  the  surface  is  oxidized,  and  this  oxide  of  iron,  being  quite  fusible 
at  this  temperature,  forms  a  complete  coating  of  slag  over  the  entire  surface. 
When  two  such  surfaces  are  brought  together,  therefore,  each  being  entirely 
covered  with  melted  iron  oxide,  which  is  practically  a  foreign  substance,  the 
union  effected  is  necessarily  imperfect.  The  degree  of  imperfection  depends 
on  the  amount  of  this  melted  slag  which  succeeds  in  remaining  in  the  joint. 
In  order  to  remove  this  liquid  slag  as  much  as  possible,  the  two  surfaces 
should  be  convex  to  each  other  when  they  are  brought  together.  That  is  to 
say,  they  should  first  come  in  contact  along  the  central  portion  of  the  weld 
area,  so  that  the  hammering  or  the  pressure  by  which  the  weld  is  effected 
will,  as  perfectly  as  possible,  squeeze  out  this  liquid  slag  from  the  joint,  thus 
allowing  the  plastic  iron  surfaces  to  come  into  immediate  and  actual  union. 
If  any  portion  of  this  melted  oxide  remains  in  the  joint,  it  entirely  prevents 
a  union  of  the  surfaces  over  such  area  as  it  occupies,  and  to  that  extent 
weakens  the  joint.  As  it  is  impracticable  to  heat  the  surfaces  to  be  welded 
or  even  to  join  them  in  a  vacuum,  or  away  from  the  oxygen  of  the  air,  it  is 
impossible  to  avoid  entirely  the  presence  of  the  melted  oxide  of  iron  in  weld- 
ing operations.  With  intelligence  and  care,  however,  in  the  performance  of 
the  work,  nearly  all  this  oxide  can  be  removed  in  the  act  of  welding,  and  a 
practically  perfect  union  effected.  To  assist  in  removing  this  melted  oxide, 
borax  is  commonly  used.  This  being  a  perfect  solvent  of  the  oxide,  the 
whole  is  changed  to  a  thin  liquid,  which  is  the  more  perfectly  squeezed  out 
of  the  joint  in  the  welding  process.  In  this  way  steel  may  be  welded  which 
would  not  unite  without  it.  When  the  parts  to  be  joined  are  heated  in  an 
ordinary  forge  the  blast  of  air  causes  an  excessive  oxidation  of  the  surfaces, 
and  thus  gives  rise  to  large  quantities  of  the  melted  slag.  By  maintaining, 
a  thick  fire  most  of  the  oxygen  has  been  consumed  to  CO  or  C02  before* 

of  a  tendency  to  crystallize  were  discovered,  and  inasmuch  as  the  metal  has  gone 
through  all  the  phases  of  deterioration  up  to  the  limit  of  actual  rupture  without  showing 
a  crystalline  tendency,  it  is  thought  this  demonstrates  and  proves  that  this  material  isi 
incapable  of  cold  crystallization  when  exposed  to  the  conditions  of  service." 

In  one  instance  one  of  the  old  cracks  which  had  developed  at  the  inner  shoulder  of 
the  journal  reached  to  a  depth  of  0.02  inch  into  the  side  of  the  test  specimen,  and  yet  I 
the  specimen  broke  two  inches  from  this'sectiou.     After  rupture  the  end  of  the  specimen 
(1|  in.  diam.)  containing  this  crack  was  bent  cold  33  degrees  with  *'  this  crack  at  the  j 
middle  of  the  bend  on  the  tension  side,  which  opened  the  crack  in  width  and  ah 
developed  numerous  cracks  in  this  vicinity,"  but  without  rupture.     All  the  tests  show* 
fibrous  fractures. 


WROUGHT  IRON.  129 

reaching  the  iron,  and  hence  less  oxide  is  formed.  If  the  parts  were  heated 
in  a  reverberatory  furnace  or  in  a  "  muffler,"  raised  to  a  sufficient  tempera- 
ture and  kept  out  of  the  way  of  air-currents,  a  much  less  amount  of  this  slag 
would  be  formed,  and  the  welding  would  be  more  readily  performed.  One 
of  the  advantages  of  electric  welding  lies  in  the  fact  that  no  air-current  is 
employed,  and  by  having  the  parts  in  contact  during  the  time  they  are  being 
heated,  the  air  is  largely  excluded  from  the  welding  surfaces,  and  hence 
little  or  no  oxide  is  formed  there  to  prevent  a  perfect  union.  It  is  largely 
for  this  reason  that  electric  welding  may  be  more  perfect  than  hand  welding. 
In  view  of  the  inherent  difficulties  described  above,  it  might  well  be 
anticipated  that  welded  joints  are  necessarily  very  unreliable  even  when  done 
with  more  than  ordinary  care.  Many  tests  of  the  strength  of  welded  joints 
have  shown  that  this  strength  may  be  anywhere  from  30  to  100  per  cent  of 
the  strength  of  the  parts  which  have  been  joined,  and  in  the  hands  of  careless 
or  incompetent  workmen  the  strength  of  a  welded  joint  may  be  almost  zero. 
With  the  most  careful  work,  however,  that  is  found  to  be  practicable  in  the 
best  forging  practice,  the  average  strength  of  hand-welded  joints  has  been 
found  by  Kirkaldy  *  to  be  in  the  case  of  round  iron  tie-bars  from  1 J  to  3-J 
inches  in  diameter,  but  60  per  cent  of  the  average  strength  of  the  bars.  In 
the  case  of  flat  plates  from  2J  to  6  inches  in  width  and  from  £  inch  to  1 
inch  in  thickness,  the  average  strength  of  the  welds  was  71  per  cent  of  the 
trength  of  the  plates.  In  the  case  of  chain-link  welds  from  £  to  2-J-  inches 
n  diameter,  the  average  of  216  tests  showed  an  average  strength  of  the  welded 
oints  of  83  per  cent  of  the  strength  of  the  iron  rods.  In  the  case  of  a 
welded  chain,  where  the  strength  of  the  chain  is  only  that  of  its  weakest  link, 
t  would  not  be  safe  to  rely  on  a  strength  of  joint  greater  than  50  per  cent 
)f  the  strength  of  the  iron  from  which  the  chain  has  been  made.* 

In  1885  Professor  Bauschinger  undertook  an  elaborate  series  of  experi- 
ments to  determine  the  relative  welding  qualities  of  soft  steel  and  wrought 
ron,  also  the  relative  efficiencies  of  forging  by  hand  and  under  a  steam- 
lammer.  The  results  of  his  experiments  have  been  condensed  in  the 
ollowing  tables.  These  results  show  a  strength  of  welded  soft-steel  bars 
jqual  to  89.2  per  cent  of  the  strength  of  the  original  material,  while  the 
fficiency  of  the  welds  of  the  wrought-iron  bars  was  95.6  per  cent.  The 
•elative  value  of  hand  and  power  forging  is  indicated  in  the  second  table, 
where  it  is  shown  that  the  hand  forging  gave  an  efficiency  of  84  per  cent, 
vhile  the  steam  forging  gave  an  efficiency  of  97.2  per  cent,  on  the  soft-steel 
)ars,  while  on  wrought  iron  these  were  87.9  per  cent  and  91.0  per  cent 
respectively. 

These  tests  were  made  under  the  most  favorable  conditions,  and  they 
probably  represent  the  highest  attainable  efficiency  in  welding  on  both  kinds 
>f  materials.  These  results  should,  therefore,  not  be  taken  as  representing 
Average  results  in  practice,  but  rather  as  an  ideal  which  may  possibly  be 

*  Kirkaldy's  System  of  Mechanical  Testing,  London,  1891,  report  KK. 


130 


THE  MATERIALS  OF  CONSTRUCTION. 


reached  with  the  greatest  care.  It  will  be  noticed  that  the  fourth  soft-steel 
specimen  gave  an  efficiency  of  99.6  per  cent,  the  break  occurring  entirely 
outside  of  the  weld ;  while  the  sixth  set  of  specimens  of  soft  steel  gave  an 
efficiency  of  but  57.3  per  cent,  the  break  occurring  in  the  weld.  Another 
specimen  of  soft  steel  would  not  weld  at  all. 

TABLE  vir. — BAUSCHINGER'S   TESTS   OF  THE  STRENGTH  OF  WELDS 

WITH    LOW-CARBON    STEEL    (iNGOT    IRON)     AND    WROUGHT    IRON. 

(Each  line  of  "  welded  "  results  contains  the  mean  of  two  tests.) 

SOFT   STEEL   OR   INGOT   IRON 


s  » 

Cross-section 

• 

Ea^ 

P3  °8 

Dimen 

of  Test-bar. 

v- 

•d 

"c3 

hM   U 

<W    ^ 

Original 
Cross- 
section 

Condi- 
tion of 
Bar. 

Method  of 
Welding. 

fl 

'3 

1 

CO 

"^ 

bti 

uo 

II 

0  O 
5  0 

Remarks. 

in  Inches. 

Dimen- 
sions. 

Area. 

i 

"3 

e 

o 
1- 

a?i 

PH    iJC 

3.15x1.18 

2.19x0.72 

1.58 

Orig. 

One  heat 

39,100 

61,860 

31.3 

59 

3.15X1.182.26X0.71 

1.60 

Welded 

Steam  hammer 

38390 

58,940 

95.3 

12.8 

14 

Both  broke  in  weld 

3.15X0.982.17X0.72 

1.56 

Orig. 

One  heat 

35,260 

59,580 

28.2 

56 

3.15x0.982.11x0.71 

1.50 

Welded 

Steam  hammer 

88,180 

62,560 

105.0 

12.5 

13 

Both  broke  in  weld! 

1.77x0.87 
1.77X0.87 

0.98x0.72 
1.07X0.70 

0  71 
0.75 

Orig. 
Welded 

One  heat 
Steam  hammer 

42,669 
44,790 

69,240 
70,740 

102.2 

23.1 
13.1 

42 
15 

Broke  in  weld 

1.34x0.590.58x0.59 

0.34 

Orig. 

Two  heats 

43,650|  69.100 

24.7 

52 

1.34X0.590.64X0.54 

0.35 

Welded 

Hand  forging 

38,390 

68,820 

99  6 

17.2 

48 

Broke  outside  of  weld 

1.26x0.55 

0.55x0.55 

0.30 

Orig. 

Two  heats          i4'>,660 

65,400 

29.8 

65 

1.26x0.55 

0.60x0.54 

0.32 

Welded 

Hand  forging 

34,840 

60,640 

92.7 

15.4 

68 

Broke  outside  of  wel( 

1.18x1.18 

d  =  0.  70 

0.39 

Orig. 

Two  heats 

46,640 

69,960 

22.8 

42 

1.18x1.18 

0.39 

Welded 

Hand  forging 

36,970 

40,100 

57.3 

0 

0 

Broke  in  weld 

d  =  1.10 

d  =  0.70 

0.39 

Orig. 

Two  heats 

33,840 

61.570 

11  9 

15 

d  =  1.06 

d  =  0.61 

0.33 

Welded 

Hand  forging 

35,550 

45,790 

74.4 

0.9 

6 

Broke  in  weld 

d  =  0.79 

d  -  0.44 

0.15 

Orig. 

Two  heats 

44,080 

66,830 

23.2 

67 

d  =  0.79 

d  =  0.44 

0.15 

Welded 

Hand  forging 

39,100 

58,230 

87.1 

8.7 

17 

Broke  in  weld 

Average  =  89.2 


WROUGHT  IRON. 


3.27X0.71 
3.27x0.71 

2.39x0.71 
2.36x0.59 

1.70 
1.39 

Or;?. 
Welu.  ' 

Three  heats 
Steam  hammer 

32,700 
24,170 

52,600 
50,050 

95.1 

26.1 
13.4 

42 
23 

Broke  in  weld 

2.56x1  00 
2.56X1.06 

1.64X0.72 
1.65x0.69 

1.18 

1.14 

Orig. 
Welded 

One  heat 
Steam  hammer 

23,750 
22,750 

50,050 
50,050 

100.0 

28.5 
20.9 

45 
34 

Broke  in  weld 

1.65X0.47 
1.65x0.47 

0.84x0.47 
0.86x0.43 

0.40 
0  37 

Orig. 
Welded 

Two  heats 
Tjand  forging 

27,730 
22,750 

51,190 
48,910 

95.6 

11.4 
8.1 

18 
14 

Broke  in  weld 

1.84x0.63 

1.34x0.63 

0.58x0.64 
0.68x0.58 

0.37 
0.40 

Orig. 
Welded 

i  "K>  heats 
i-/.-?d  forging 

28,440 
27,020 

56,880 
55,450 

97.6 

24.3 
15.3 

42 

Broke  in  weld 

1.02x1.02 

1.02x1.02 

d  -  1.02 
d=  1.02 

d  =  0.59 
d  -  0.59 

0  >tf 
0.27 

Orig. 
Welded 

Orig. 
Welded 

Two  heats 
Hand  forging 

29,860 
28,440 

55,030 
56310 

102.3 

31.5 
15.6 

18.3 
9.2 

39 
17 

36 
16 

Broke  near  weld 

d  =  0.59 
d  =  0  59 

0.27 
0.27 

Two  heats 
Hand  forging 

29,860 
27,020 

61,000 
50,620 

83  0 

Broke  in  weld 

Average  =  96.6 

WROUGHT  IRON. 


131 


TABLE  viii. — BAUSCHINGER'S  TESTS  OF  THE  RELATIVE  VALUE  OF 

HAND   AND    STEAM    FORGING. 

(Welding  Low-carbon  Steel  and  Wrought  Iron.) 

SOFT  STEEL  OR  INGOT  IRON. 


Dimen- 
•     sions  of 
Original 
Cross- 
section 
in  Inches. 

Cross-section 
of  Test-  bar. 

Condi- 
tion of 
Bar. 

Method  of 
Welding. 

43 

a 

0 

Cu 

i 

42.660 
47,200 
47,490 

Tensile  Strength. 

co  .  Original 

Welded  . 

o^£  1  Percentage  of  Elon- 
co-?co  gation  for  10  Inches. 

Percentage  of  Re- 
duction of  Area. 

Remarks. 

Dimen- 
sions. 

Area. 

1.26x0.47 
1.26x0.47 
1.26x0.47 

0.81x0.41 
0.82X0.36 
0.80x0.35 

d  =  0.43 
d  =  0.43 

d  =  0.43 

0.33 
0.30 

0.28 

Orig. 
Welde'd 
Welded 

Hand  forging 
Steam  hammer 

68,110 
68,250 
71,100 

9.2 
to 

66 
66 
62.5 

Broke  outside  of  weld 
Broke  outside  of  weld 

0.75X0.75 
0.75X0.75 
0.75X0.75 

0.14    Orig. 
0  14    Welded 
0.14    Welded 

Hand  forging 
Steam  hammer 

45,640  66,260 
44,22061,710 

39.810J  65,551) 

93.1 
98.9 

21.7 
9.1 
13.0 

68. 
9 
36 

Broke  in  weld 
Broke  in  weld 

d  =  1.02 
d  =  1^02 

d  =  0.59 
d  =  0.58 
d  =  0.58 

0.2? 
0.27 
0.27 

Orig. 
Welded 
Welded 

Hand  forging 
Steam  hammer 

42,230 

24,880 
33,130 

62,700 
27,300 
54,600 

43.5 

87.1 

22.9 
0.1 
6.9 

63 
1 

18 

Broke  in  weld 
Broke  in  weld 

d  =  0.9l 
d  =  0.91 
d  =  0.91 

d  =  0.51 
d  =  0.51 
d  =  0.51 

0.21 
0.21 
0.21 

Orig. 
Welded 
Welded 

Hand  forging 
Steam  hammer 

49,200 
44,930 
44,930 

09,530 

68,960 
68,400 

99.2 
98.4 

23.0 
15.8 
14.8 

62 
28.5 
20 

Broke  in  weld 
Broke  outside  of  weld 

Average  hand  forging  =  84.0 
steam               =97.2 

WROUGHT   IIION. 

d  =  1.02 
d=  1.02 
d=  1.02 

d  =  0.58 
d  =  0.58 
d  =  0.58 

0.27 
0  27 
0.27 

Orig. 
Welded 
Welded 

Hand  forging 
Steam  hammer 

24,880 
24,880 
27,020 

55,460 
48,770 
50,480 

87.9 
91.0 

23.1 
9.9 
12.7 

41 
10.5 
35 

Broke  in  weld 
Broke  outside  of  weld 

95.  The  Effect  of  Reduction  in  the  Rolls  on  the  Strength  of  Wrought 
Iron.* — Other  things  being  equal,  the  strength  of  wrought  iron  will  vary 
directly  with  the  amount  of  reduction  in  the  rolls  from  the  size  of  the  pile  to 
that  of  the  finished  specimen.  If  it  is  desired  to  obtain  an  equal  strength 

TABLE    IX. — EFFECT    OF    VARYING     REDUCTION     IN     THE     ROLLS     ON     THE 
STRENGTH    OF    WROUGHT    IRON. 


Diameter. 

Length. 

Elastic  Limit. 

\b*r 
Ultimate  Strength. 

Per  Cent  of 
Elongation. 

Ratio  of  Elastic 
Limit  to  Ulti- 
mate Strength. 

1 

4.75 

38,000 

57,533 

17.1 

66.1 

n 

6/25 

34,600 

54,85 

21.65 

62.9 

it 

7.50 
8.50 

32,600 
34,800 

58,  3f 

52,6'  > 

23.5 
26.0 

60.8 
65.7 

H 

0.75 

33,100 

52,400 

25.3 

63.3 

li 

8.175 

34,325 

54,175 

22.0 

63.4 

If 

9.50 

33,175 

52,000 

23.15 

63.6 

n 

9.75 

31,875 

50,325 

23  2 

63.8 

2 

10.50 

31,800 

49,725 

22.3 

63.9 

*  See  also  similar  results  on  steel  in  Chap.  XXV. 


132 


THE  MATERIALS  OF  CONSTRUCTION. 


for  different  finished  sizes,  it  is  necessary  to  make  these  several  sizes  from 
the  piles  whose  areas  of  cross-section  bear  a  constant  ratio  to  those  of  the 
finished  sections.  The  following  table  gives  average  results  of  four  series  of 
tests  on  wrought  iron  on  sizes  from  one  inch  to  two  inches  in  diameter. 

As  showing  that  a  uniform  reduction  in  the  rolls  may  be  made  to  produce 
iron  of  equal  strength  for  these  same  sizes,  the  following  table  of  results  is 
given,  the  iron  having  been  rolled  and  the  tests  of  strength  made  expressly 
to  establish  this  fact.* 

TABLE  X. — DIMENSIONS  AND  AREAS  OF  PILES,  AEEAS  OF  BARS  IN 
PERCENTAGE  OF  AREAS  OF  PILES,  TENSILE  STRENGTH,  ELASTIC 
LIMIT,  ETC.,  OF  NINE  BARS. 


Size  of  Bar. 

Dimensions  of 
Piles. 

Area  of  Piles. 

Area  of  Bars  in 
Per  Cent  of 
Area  of  Piles, 

Tensile  Strength. 

Elastic  Limit. 

Inches. 

Inches. 

Sq.  In. 

Per  Cent. 

Pounds. 

Pounds. 

2 

8  X  10 

80 

3.92 

50,763 

33,258 

If 

8  X  10 

80 

3.45 

53,361 

35,032 

If 

8X9 

72 

3.34 

53,154 

35,323 

If 

8x8 

64 

3.24 

53,329 

33,520 

tt 

6X9 

54 

3.27 

52,819 

34,840 

H 

6X7 

42 

3.53 

52,733 

34,606 

li 

6x6 

36 

3.41 

53,248 

33,520 

H 

6X5 

30 

3.31 

54,648 

34,695 

1 

5X5 

25 

3.14 

53,915 

36,287 

*  These  two  tables  of  results  are  compiled  from  data  given  in  the  report  of  the  U.  S.. 
Board  on  Testing  Iron  and  Steel,  vol.  i,  1881. 


CHAPTER  IX. 

STEEL. 
METHODS   OF  MANUFACTURE. 

96.  The  Crucible  Process  is  the  oldest  and  simplest  of  those  used  at  the 
present  time,  and  is  still -used  for  the  finer  grades  of  tool-steel.     A  pure 
grade  of  wrought  iron  is  first  rolled  into  flat  bars  and  cut  into  convenient 
lengths.     These  are  then  heated  for  from  three  to  six  days  in  "  cementing 
furnaces,"  where  they  are  tightly  enclosed  in  boxes  separated  by  layers  of 
fine  charcoal.     This  recarburizes  the  wrought  iron  at  the  rate  of  about  -J- 
inch  in  depth  every  twenty-four  hours,  and  makes  cement  or  blister  steel.* 
This  was  the  steel  of  commerce  until  1740,  when  it  was  first  remelted  in 
crucibles  (by  Daniel  Huntsman,  in  England),  thus  making  what  is  still 
known  as  crucible  steel.     These  crucibles  are  now  heated  in  a  Siemens  re- 
generative gas-furnace,  simliar  to  that  described  in  Art.  98.     Cheaper  grades 
of  crucible  steel  are  made  by  remelting  in  crucibles  Bessemer  scrap.     The 
cheaper  Bessemer  and  open-hearfJt  processes  have  now  limited  the  use  of 
the  crucible  process  to  the  manufacture  of  high-grade  tool  and  spring  steel 
only.     In  1896  the  total  annual  capacity  of  crucible-steel  furnaces  in  the 
United  States  was  about  100,000  gross  tons. 

97.  The  Bessemer  Process. — This  consists  of  a  decarburization'  of  crude 
pig  iron  by  means  of  finely  divided  air-currents  blown  through  the  iron  when 
in  a  melted  state.     The  oxygen  in  the  air  burns  out  the  silicon  and  carbon 
from  the  melted  cast  iron,  and  this  combustion  so  raises  the  temperature  of 
the  melted  mass  that  it  remains  a  mobile  fluid  even  after  these  foreign  in- 
gredients have  been  almost  wholly  removed.     This   requires  a  very  high 
temperature  indeed,  and  one  which  could  not  be  obtained  in  the  ordinary 
puddling-furnace.     The  purified  iron  is   then   "recarburized"  by  adding 
melted  spiegeleisen  which  contains  from  10  to  20  per  cent  of  manganese, 
and  also  some  carbon  and  silicon.     This  manganese  unites  with  the  large 
amount  of  oxide  of  iron  present,  which  was  formed  by  the  blast,  and  which 
would  cause  the  product  to  be  red-short  and  to  crumble  in  working,  and 


*Also  called  shear,  double  shear,  or  German  steel. 

133 


134 


THE  MATERIALS  OF  CONSTRUCTION 


at  the  same  time  the  proportion  of  carbon  is  brought  up  to  any  desired 
amount.  The  whole  mass  is  then  poured  off  into  ladles,  and  thence  into 
cast-iron  moulds.  These  masses  of  cast  steel  are  now  called  ingots.  This 
process  was  invented  by  Sir  Henry  Bessemer  of  England,  and  perfected  by 
G.  F.  Goranssou  of  Sweden,*  in  1858. 

In  this  process  the  crude  melted  iron  is  tapped  directly  from  the  cupola 
furnace,  and  in  Sweden  directly  from  the  blast-furnace  into  the  converter, 
which  is  a  large  steel  vessel,  mounted  on  trunnions,  lined  with  refractory 
materials,  with  a  removable  bottom  provided  with  many  small  openings 
or  tuyeres.  This  vessel  is  turned  down  into  a  horizontal  position  to 
receive  its  charge.  The  blast  is  then  started  and  the  vessel  raised 
to  a  vertical  position,  the  air-pressure  being  sufficient  to  keep  the 
melted  iron  from  entering  the  air  openings  in  the  base.  In  Sweden, 
where  a  very  pure  iron  is  used,  the  blast  is  stopped  when  the  appearance  of 
the  shower  of  sparks  issuing  from  the  mouth  of  the  converter  indicates  the 


TIME   /N   MINUTES 


0  2  4-     •  6 

FIGt  62. — Chemical  Reductions  of  au  Open-hearth  Converter.     (Howe,  Jour.  IT.  & 
St.  Inst.,  vol.  n.  p.  102.) 

desired  percentage  of  carbon,  when  the  metal  is  at  once  poured  off  into  the 
moulds.  As  this  criterion  is  a  very  uncertain  one,  it  is  customary  in  this 
country  to  continue  the  blast  till  practically  all  the  carbon  has  been  con- 
sumed, this  stage  being  clearly  indicated  by  the  changed  appearance  of  the 
flames.  The  addition  now  of  manganese  and  carbon,  in  any  desired  pro- 
portions, is  readily  made.  It  is  important  to  remember  that  by  this  process 
no  sulpliur  or  phosphorus  is  removed,  and  hence  only  pig  irons  compara- 
tively free  from  these  elements  can  be  used  for  the  Bessemer  process,  such 
iron  being  known  as  Bessemer  pig.  The  iron  must  contain  from  1|  to  2£ 
per  cent  of  silicon  in  order  that  by  its  combustion  it  may  sufficiently  heat 
the  charge  to  keep  it  fluid  when  the  carbon  is  consumed.  If  there  is  as 
much  as  2J  per  cent  of  silicon  in  the  pig-iron,  from  10  to  15  per  cent  of 


*  See  paper   by  Prof.  Rich.  Ackerman    of  Stockholm,   in   Trans.  Am.   Soc.  Min. 
Engrs.,  vol.  xxn.  p.  266. 


STEEL. 


135 


cold  steel  scrap  can  also  be  worked  into  the  charge  without  chilling  it. 
The  rate  of  burning  the  silicon,  carbon,  and  manganese  is  shown  in  Fig.  62. 
The  combustion  of  the  silicon  brings  to  the  mass  about  nine  times  as  much 
heat  as  the  combustion  of  the  same  amount  of  carbon.  One  reason  for  this 
is  that  the  products  of  the  combustion  of  silicon  form  a  slag  which  remains 


FIG.  63. — Plan  and  Sectional  View  of  a  Bessemer-steel  Plant. 

in  the  converter,  while  the  product  of  the  combustion  of  carbon  is  a  gas 
which  passes  off  and  carries  much  heat  with  it. 

In  Figs.  63  to  67  are  shown  the  characteristic  features  of  a  standard 
American  Bessemer-steel  plant.  On  the  right  of  Fig  63,  in  plan,  are 
hown  four  cupola-furnaces,  with  a  blower,  for  melting  the  pig  iron.  The 
sectional  view  shows  these  to  be  placed  at  a  high  elevation,  so  that  the 
melted  iron,  received  in  the  ladles  K,  which  stand  on  platform-scales  for 
weighing  the  charge,  can  be  poured  into  the  spouts  M N9  and  run  directly 
into  the  mouth  of  the  converter,  which  is  then  turned  into  the  position 
shown  in  Fig.  65.  The  blast  is  now  started  through  the  base  of  the  con- 
verter, and  it  is  raised  to  a  vertical  position,  Fig.  66,  and  the  blast  kept  on 


136 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG,  64.-Views  of  the  American  Form  of  Bessemer  Converter,  showing  the  Movable 

Bottom. 


65.— Receiving  the  Charge. 


STEEL. 


137 


till  first  the  silicon  and  then  the  carbon  has  been  burned  out.  The  con- 
verter is  then  again  revolved  to  a  hori- 
zontal position,  and  the  blast  stopped. 
The  proper  amount  of  melted  spiegel- 
eisen  which  is  kept  melted  in  the  two 
reverberatory  furnaces  RR  is  then  run 
into  the  converter,  whereupon  it  is  at 
once  poured  into  the  ladle,  which  is 
operated  by  a  crane  which  swings  it  in 


FIG.  66. — The  Bessemer  Converter   in 
Action. 


FIG.  67.—  The  Valvular  Ladle. 


the  path  of  a  circle  over  the  several  ingot-moulds,  the  metal  falling 
through  a  valve  at  the  bottom,  as  shown  in  Fig.  G7.  The  motions  of  the 
converter  and  also  of  the  crane,  as  well  as  the  blast,  are  all  controlled  from 
one  platform  by  levers  operating  hydraulic  machinery. 

The  Swedish  practice  of  taking  the  iron  directly  from  the  blast-fur- 
nace is  growing  in  this  country,  but  it  is  here  first  run  into  a  large  vessel 
containing  from  100  to  150  tons  of  melted  iron,  called  a  mixer,  in  order  to 
obtain  a  more  uniform  product.  This  mixer  also  serves  as  a  reservoir  for 
equalizing  the  inequalities  of  supply  from  the  blast-furnace  and  demand 
from  the  converter.  From  this  mixer  it  is  drawn  into  ladles  on  cars,  and 
run  to  an  elevated  platform  and  poured  into  the  converter.  This  is  called 
the  direct  process.  It  may  be  employed  when  the  blast-furnaces  are  re- 
moved from  the  Bessemer  plant  as  far  as  one  or  two  miles. 

Recently  a  means  of  removing  phosphorus  has  been  found  in  the  addi- 
tion of  calcined  lime  to  the  charge  in  the  converter.*  The  phosphorus 
unites  with  the  lime  and  so  passes  into  the  slag.  In  this  case  the  lining  of 
the  converter  must  also  be  "  basic  "  to  keep  the  slag  from  uniting  with  it 
and  so  rapidly  consuming  it,  so  the  lining  is  then  made  of  a  calcined  mag- 
nesian  limestone  (dolomite)  and  tar,  made  into  brick,  or  rammed  into  place. 
This  is  called  the  basic  Bessemer  process,  but  its  use  had  been  abandoned 
in  America  because  of  some  unfortunate  failures  when  first  introduced. 


*By  S.  G.  Thomas  and  P.  C.  Gilehrist,  England,  1878. 


138 


THE  MATERIALS  OF  CONSTRUCTION. 


The  method  has  now  (1896)  been  revived  at  Troy,  N.  Y.,  with  marked 
success. 

The  Bessemer  is  the  cheapest  known  process  of  making  steel.  This 
process  alone  has  revolutionized  many  lines  of  industry,  and  has  led  to  the 
replacing  of  wrought  iron  by  steel  in  all  the  more  important  uses  of  these 
materials.  The  Bessemer  process  is  now  used  exclusively  for  making  steel 
rails  for  steam  and  electric  roads,  and  for  all  the  cheaper  grades  of  steel 
plates  and  structural  forms.  For  the  better  grades  of  structural  material  it 
is  being  replaced  by — 

98.  The  Open-hearth  Process. — In  this  process  pig  iron,  cast  iron,  and 
wrought-iron  and  steel  scrap  are  converted  into  steel  under  the  direct 
action  of  an  oxidizing  flame  in  a  regenerative  gas-furnace.  It  was  patented 
in  1845  by  Heath,  but  was  not  found  to  be  successful  until  Siemens  had 
developed  his  regenerative  gas-furnace  about  1862.  Since  about  1870 


Am.BiukNot.Co.N.I. 


FIG.  68.— Transverse  Section  of  a  Typical  Open-hearth  Regenerative  Gas-furnace. 


these  furnaces  have  multiplied  rapidly,  and  in  1896  the  total  capacity  of 
these  furnaces  in  the  United  States  was  2,400,000  gross  tons,  as  against  a 
total  capacity  of  9,400,000  gross  tons  by  the  Bessemer  process. 

The  more  common  type  of  furnace  used  for  this  purpose  is  shown  in 
Figs.  68  and  69.  The  fuel  used  is  what  is  known  as  producer-gas.  This 
is  a  mixture  of  carbonic  oxide  and  hydrocarbons,  diluted  with  about  60 
cent  of  nitrogen.  It  is  formed  in  gas  producers  in  which  coal  is  burned  h 
air-tight  ovens  with  an  insufficient  supply  of  air,  this  supply  being  fed  ii 


STEEL. 


139 


under  pressure  and  in  known  volumes.  This  producer-gas  is  brought  to 
the  hearth  area  of  the  open-hearth  furnace  through  a  passageway  entirely 
filled  with  red-hot  fire-brick  stacked  to  form  an  open  checker-work,  as 
shown  at  E  and  F  ir  Figs.  68  and  69. 


FIG.  69. — Longitudinal  Section  of  a  Typical  Open-hearth  Regenerative  Gas-furnace. 

As  this  hot  gas  enters  the  furnace  area  it  is  mixed  with  streams  of  hot 
air  which  has  also  been  drawn  in  over  red-hot  brick  surfaces,  and  the  com- 
mingling of  these  red-hot  gases,  in  proper  proportions  to  produce  complete 
combustion,  develops  the  most  intense  heat  possible  to  obtain  by  the  com- 
bustion of  gases.  In  the  reverberatory  furnace.,  where  the  flame  of  an 
ordinary  coal  fire  is  emplo}^ed,  the  maximum  temperature  attainable  is 
about  3,500  degrees  F.,  but  in  the  Siemens  regenerative  gas-furnace  a  tem- 
perature of  4500  degrees  F.  may  be  maintained.  The  regenerative  princi- 
ple consists  in  the  utilization  of  the  heat  of  the  escaping  gases  in  reheating 
the  fire-brick  placed  in  the  air  and  gas  passageways.  To  do  this  it  is  of 
course  necessary  to  alternate  the  incoming  and  the  escaping  gases  in  two 
sets  of  passages,  this  being  done  by  simply  moving  certain  valves  every 
twenty  or  thirty  minutes. 

In  Fig.  68  Jris  the  furnace  hearth;  EE  are  air-chambers  and  FF gas- 
chambers,  the  checker  brickwork  being  shown  in  one  only  of  each,  but  it 
really  fills  all  four  of  these  passageways.  The  red-hot  gas  enters  the 
furnace  through  the  lower  ports  H,  Fig.  68,  and  BE,  Fig.  69;  while  the  air 
enters  just  above  these  through  an  annular  space  /,  Fig.  68,  and  C,  Fig. 
69.  The  furnace  itself,  therefore,  is  like  a  great  argand  gas-burner  in  its 
method  of  receiving  and  burning  the  gas.  The  depressed  roof  of  the  fur- 
nace throws  the  heat  strongly  upon  the  materials  placed  on  the  hearth, 


140  THE  MATERIALS  OF  CONSTRUCTION. 

while  the  gases  themselves  are  forced  to  play  upon  the  melting  metal.  The 
flame  has  an  excess  of  oxygen  so  that  it  is  an  oxidizing  flame,  and  would 
rapidly  waste  unmelted  wrought-iron  or  steel  scrap  placed  in  it.  It  is  cus- 
tomary, therefore,  to  place  first  on  the  hearth  pig  or  cast  iron  on  which  the 
oxidizing  flame  acts  by  consuming  first  the  silicon  and  then  the  carbon,  at 
the  same  time  oxidizing  some  iron  which  by  melting  forms  a  slag  which 
floats  on  the  bath  of  melted  metal.  After  such  a  bath  has  been  prepared 
the  wrought-iron  and  steel  scrap  can  be  thrown  in,  since  these  will  now  be 
covered  by  the  bath  and  so  protected  from  the  oxidizing  flame.  The 
facility  with  which  such  scrap  can  be  remelted  and  made  over  into  new 
ingots  by  this  method  is  one  of  its  chief  elements  of  value.  If  one  could 
always  choose  his  ingredients  at  pleasure  he  could  so  proportion  them  that 
little  or  no  decarburizatiou  would  be  necessary,  a  simple  melting  together 
giving  the  requisite  proportions. 

The  final  removal  of  any  excess  of  carbon,  after  the  products  have  melted, 
is  effected  by  means  of  the  melted  oxide  of  iron,  which  floats  on  the  surface 
at  first,  but  which  afterwards  becomes  thoroughly  mixed  with  the  mass  by 
the  boiling  action  of  the  escaping  gases  when  the  temperature  becomes  high. 
Some  of  the  oxygen  of  this  iron  oxide  combines  with  the  carbon  of  the 
melted  iron  and  comes  to  the  surface  as  carbonic  oxide,  where  it  is  burned  to 
dioxide  and  passes  out  with  the  other  consumed  gases.  This  also  restores 
a  corresponding  portion  of  the  iron  of  the  oxide  slag  to  the  metal  bath  and 
so  adds  to  the  product. 

When  a  large  amount  of  pig  or  cast  iron  is  to  be  reduced,  it  is  common 
to  charge  a  suitable  air  ant  of  oxide  of  iron  ore  to  supply  the  requisite 
amount  of  oxygen  to  decarbonize  the  cast  iron,  and  so  to  hasten  the  process 
and  also  to  avoid  the  necessity  of  creating  so  much  artificial  oxide  of  iron  by 
the  oxidizing  flame.  The  remaining  portion  of  the  oxide  slag  not  destroyed 
by  giving  up  its  oxygen  to  the  carbon  in  the  bath  is  neutralized  and  chemi- 
cally destroyed  by  adding  a  charge  of  spiegeleisen  containing  20  or  30  per 
cent  of  manganese,  or  an  artificial  f erromanganese  containing  some  80  per 
cent  of  manganese,  just  before  pouring.  The  manganese  unites  with  the 
oxygen  of  the  slag,  and  restores  the  iron  to  the  bath  the  same  as  is  done  in 
the  Bessemer  process.  There,  however,  it  was  usually  desired  to  add  carbon 
also,  and  hence  this  process  has  come  to  be  known  as  recarburization,  or  the 
adding  of  a  recarburizer.  In  the  open-hearth  process  the  carbon  is  not  all 
burned  out,  as  it  is  in  the  Bessemer  process,  but  by  taking  samples  out  with 
a  sn^l  dipper  or  ladle,  and  casting  these,  cooling  them  in  water,  and  break- 
ing them,  the  operator  can  tell  when  he  has  the  carbon  ingredient  brought 
to  the  desired  amount.  He  seldom  wants  to  add  carbon,  therefore,  in  the 
open-hearth  process,  but  must  add  the  manganese  to  destroy  the  oxide  slag" 
which,  if  poured  off  with  the  iron,  would  make  it  red-short,  or  unmali^uble 
in  the  rolls.  The  manganese  charge  should  more  properly  be  called  a 
"  deoxidizer,"  but,  by  analogy  from  the  Bessemer  process,  the  same  term  of 
"  recarburizer"  is  applied  here  to  :'  !j  manganese  charge. 


STEEL.  141 

The  pervasive  action  of  this  manganese  charge  in  the  open-hearth  furnace 
is  very  remarkable.  The  manganese  has  so  strong  an  affinity  for  the  oxygen 
in  the  iron  oxide  that  it  seems  quickly  to  seek  it  out  throughout  all  parts  of 
the  bath,  and  even  when  added  to  the  metal  in  the  ladle,  after  teeming, 
it  seems  to  be  equally  effective.  In  the  case  of  the  Bessemer  process,  how- 
ever, it  is  necessary  not  only  to  destroy  the  iron  oxide,  but  to  add  a  carbon 
ingredient  to  the  metal.  To  secure  a  uniform  distribution  of  this  carbon 
element  through  the  mass  seems  to  require  a  thorough  artificial  mixing. 
The  only  action  of  this  kind  which  is  secured  in  the  Bessemer  process  is  had 
in  the  pouring  off  into  the  ladle  and  the  drawing  from  the  pouring-nozzle  in 
its  bottom  into  the  ingot-moulds.  This  does  not  insure  a  uniform  distribu- 
tion of  the  carbon,  and  hence  it  is  not  very  uncommon  to  find  great  differ- 
enced in  the  mechanical  qualities  of  different  portions  of  the  same  sheet  of 
Bessemer  steel.  In  the  open-hearth  process  little  or  no  carbon  is  added  in 
the  "  recarburizer,"  so  that  the  mixture  retains  the  homogeneity  it  neces- 
sarily secures  from  the  violent  boiling  action  of  the  bath.  This  greater 
homogeneity  and  reliability,  when  judged  by  sample  tests,  has  led  to  a 
general  preference  for  open-hearth  steel  by  engineers  in  all  kinds  of  struc- 
tural designing. 

Here,  as  in  the  Bessemer  process,  there  is  no  elimination  of  the  phos- 
Iphorus  and  of  the  sulphur.  This  has  greatly  limited  the  range  of  materials 
which  could  be  fed  to  this  furnace,  and  it  has  led  here,  as  in  the  case  of  the 
[Bessemer  process,  to  the  use  of  a  charge  of  calcined  lime  to  unite  with  the  excess 
f  phosphorus*  and  hold  it  in  the  slag,  which  is  then'  drawn  off.  But,  as  with 
(the  Bessemer  furnace,  this  lime  would  unite  with  ihe  sand  lining  of  the 
(furnace  to  form  a  flux  which  would  quickly  destroy- this  lining  altogether. 

0  prevent  this,  those  furnaces  in  which  lime  is  to  be  added  to  4the  charge 
re  themselves  lined  with  calcined  dolomite  limestone,  and  these  are  called 
asic-lined  furnaces,  and  this  process  has  thus  come  to  be  known  as  the  basic 
pen-hearth  process.     It  must  be  understood,  however,  that  neither  here  nor 

1  the  Bessemer  process  docs  the  lining  play  any  part  in  the  process  itself. 
'he  process,  in  each  case,  depends  on  the  materials  charged  and  not  011  the 
urnace  lining.     The  lining  is  simply  made  such  as  will  not  be  attacked  by 

slag  formed,  and  is  always  intended  to  be  neutral,  or  inert.  In  1896 
bout  one  half  of  the  open-hearth  steel  made  in  the  United  States  was  by 

basic  process. 

To  distinguish  the  ordinary  open=hearth  process,  in  which  a  sand  or 
ilica  lining  is  used  and  no  lime  fed  in  the  charge,  that  is  to  say,  in  will  'i 
o  attempt  is  made  to  remove  any  qf  the  phosphorus  in  the  ingredients  used, 
rom  this  "  basic  "  process,  the  former  is  now  called  the  acid  open-hearth 
rocess.  It  was  formerly  known  as  the  Siemens-Martin  process,  from  its  use 
the  ^iemens  furnace  and  from  the  fact  that  the  Messrs.  Martin  of  France 


*  When  steel  is  very  low  in  carbon  some  phosphorus,  as  0.03  or  0.04  per  cent,  seems 
esiruble  to  add  strength  to  the  metal.  -ru.f 


142  THE  MATERIALS  OF  CONSTRUCTION. 

first  employed  tlie  open-hearth  in  this  way,  but  without  the  Siemens  regen- 
erative gas-furnace. 

99.  Comparison  of  the  Basic  and  Acid  Open-hearth  Processes. — From 
what  has  been  given  in  the  previous  article  it  is  evident  that  poor  steel  and 
steel  high  in  phosphorus  may  be  made  by  either  process,  due  to  ignorance, 
carelessness,  or  inexperience.     By  the  use  of  the  basic  process  ingredients 
high  in  phosphorus  may  be  employed,  and  thus  the  available  materials  are 
very   much    increased   and   hence  cheaper  grades  can  be  employed.     The 
process  itself  is  somewhat  more  expensive  than  the  acid  process.     When  the 
acid  process  is  used,  unless  there  is  a  rigid  inspection  and  control  over  the 
product,  there  is  a  danger  that  the  cheaper  (phosphorus)  ingredients  may  be 
used,  and  so  lead  to  a  brittle  product,  whereas  if  the  basic  process  be  speci- 
fied and  employed  the  cheaper  ingredients  are  anticipated,  and  the  removal 
of  the  phosphorus  provided  for.     The  maker  can  be  trusted  to  reduce  the 
sulphur  in  order  to  make  the  product  malleable  when  hot,  so  as  to  roll 
smoothly,  as  defects  here  are  patent  to  any  one.     Engineers  now  generally 
specify  the  open-hearth  process  without  prescribing  the  kind  of  lining,  but- 
naming  a  maximum  proportion  of  phosphorus.     This  upper  limit  of  phos- 
phorus is  now  commonly  taken  at  from  0.06  to  0.08  per  cent,  but  Mr.  II.  H,t 
Campbell,*  who  is  the  highest  authority  from  the  standpoint  of  the  manu 
facturer,  says  this  upper  limit  should  now  be  made  0.04  per  cent.     If  tin 
phosphorus  limit  is  not  specified,  or  if  specified  but  not  determined  by  actua 
tests,  then  it  would  be  safer  to  specify  the  basic  open-hearth  method,  f 

100.  Comparison  of  Bessemer  and  Open-hearth  Steel. — Comparing  th 
products  only  (not  the  processes)  of  these  two  general  methods  of  makin; 
steel  on  a  large  scale,  we  may  say : 

1.  While  for  like  chemical  analyses  like  mechanical  properties  may  b 
anticipated  from  these  two  methods,  yet  all  the  unexplained  accidental  failure 
of  steel  have  occurred  on  Bessemer  steel.     Engineers  have  become  suspicion 
of  it.     Open-hearth  steel  is  therefore  more  reliable  than  Bessemer  steel. 

2.  Test  specimens  cut  from  different  parts  of  the  same  Bessemer  ste<* 
plates  have  shown  extraordinary  differences  in  their  mechanical  propertie 
This  has  never  been  found  in  open-hearth  plates.     They  are  therefore  mo\ 
homogeneous  than  Bessemer  plates. 

3.  Bessemer  steel  products  found  on  the  general  market  are  apt  to 
extremely  irregular  in  their  composition,  though  rolled  into  like  forms  ar 
eold  to  serve  the  same  purposes.     Open-hearth  products  purchased  in  the  op< 
market  and  designed  to  serve  the  same  purposes  are  more\uniform  in  qualit 

4.  The  open-hearth  steel  may  be  tested  before  tapping  off,  and  its  coi 
•position  adjusted  at  pleasure,   and  this  is  usually  done.     Bessemer  st 


*  Superintendent  Pennsylvania  Steel  Co.,  Steelton,  Pa. 

f  In  January,  1896,  there  were  in  operation  in  the  United  States  opeu-hearth-st 
plants  having  an  annual  capacity  of  2,430,000  gross  tons,  700,000  of  which  capacity  1 
been  added  in  the  preceding  two  years,  more  than  one  half  of  them  using  the  "  basi 
process.  Thirteen  of  these  new  furnaces  are  to  be  used  in  making  steel  castings. 


STEEL. 


143 


TABLE    XI. — TESTS    SHOWING    THE    HOMOGENEITY   OF    OPEN-HEART    META*L"\^ 


Heat  10,699.     Acid  Open-hearth. 

Heat  10,910.     Acid  Open-hearth. 

Test-bars,  f"  rolled  rounds. 

Test-bars,  1£"  rolled  rounds. 

Elastic  Limit, 
Lbs.  per  Sq.  In. 

Ultimate 
Strength, 
Lbs.  per 
Sq.  In. 

Elongation 
in  8  In., 
Per  Cent. 

Reduction 
of  Area, 
Per  Cent. 

Elastic  Limit, 
Lbs.  per  Sq.  In. 

Ultimate 
Strength, 
Lbs.  per 
Sq.  In. 

Elongation 
in  Bin., 
Per  Cent. 

Reduction 
of  Area, 
Per  Cent. 

35,900 

53,510 

28.75 

64.14 

31,140 

52,760 

32.75 

60.60 

36,450 

54,790 

31.75 

64.58 

31,790 

52,750 

32.75 

61.20 

36,000 

56,150        28.75 

62.71 

31,540 

53,000 

31.50 

56.50 

SO,  225 

55,690        31.25 

64.48 

31,250 

52,000 

32.25 

63.30 

36,090 

55,830 

31.00 

64.71 

31,250 

52,320 

34  00 

64.10 

36,315 

55,830 

32.00 

65.18 

31,080 

52,320 

32.50 

57.10 

36.740 

56,370 

31.50 

64.84 

31,160 

52,830 

32.75 

61.80 

36,350 

55,090 

29.50 

62.87 

31,250 

53,160 

32.75 

58.10 

36,450 

57,510 

31.25 

64.25 

31,040 

52,160 

32.75 

61.80 

36,125 

56,900 

30:75 

64.26 

32,050 

53,840 

32.50 

59.60 

37,580 

56,600 

33.50 

64.16 

31,660 

53,580 

32.50 

61.10 

36,900 

57,510        30.50 

65.16 

31,700 

52,480 

32.25 

53.10 

37,220 

57,420 

31.25 

63.28 

32,550 

52,580 

34.00 

63.10 

37,130 

57,280 

31.75 

64.16 

32,570 

52,960 

32.75 

65.40 

36,000 

57,050 

31.25 

65  .  75 

33,330 

53,050 

33.00 

60.40 

35,860 

57,190 

31.25 

64.23 

33,580 

53,860 

33.00 

60.40 

36  615 

57,440 

31.25 

64.74 

36,450 

57,670 

31.75 

66.46 

37,165 

57,580 

32  .  75 

63.68 

36,640 

57,350 

31.25 

63  .  18 

56,538 

Av.  36,510 

31.15 

64.34 

Av.  31,809 

52,853 

32.75          60.48 

i 

1 

Heat  11,018.     Acid  Open-hearth. 

Heat  1,820.     Basic  Open-hearth. 

Test-bars,  f"  rolled  rounds. 

Test-bars,  %''  rolled  rpuuds. 

Elastic  Limit, 
Lbs.  per  Sq.  In. 

Ultimate 
Strength, 
Lbs.  per 
Sq.  lu. 

Elongation    Reduction 
in  8  In.,     (    of  Area, 
Per  Cent.      Per  Cent. 

Elastic  Limit, 
Lbs.  per  Sq.  In. 

1  Ultimate 
Strength, 
Lbs.  per 
Sq.  In 

Elongation 
in  8  In., 
Per  Cent. 

Reduction 
of  Area, 
Per  Cent. 

36,700 

58,400 

28.00          66.20 

33,065    !     48.340 

34.50 

71.87 

37,150 

57,840 

30.75 

65.60 

31,530        47,380 

35.00          72.05 

37,280 

56,880 

29.50 

58.60 

33,650 

48,450 

35.00 

72.05 

36,060 

56,940 

28.50 

53.30 

31,600 

48,230 

37.00 

74.14 

36,420 

56,700 

30.75 

63.10 

33,340 

49,  1  75 

36.25 

70.09 

36,060 

57,180 

30.25 

65.50 

32,760 

48.560 

33.75 

79.25 

35,780 

56,800 

31.00 

65.40 

33,260 

47,730 

35.00 

74.49 

36,700 

57,440 

30.00 

63.80 

32,130 

48,785 

34.00 

71.80 

35.780 

56,800 

31.00 

65.40 

32,935 

48,640 

34.25 

71?92 

36,700 

57,440 

30.00 

63.80 

33,270 

49,440 

34.00 

71.48 

35,700 

56,900 

32.50     ,     67.10 

32,900 

47,835 

34.00 

72.72 

37,020 

57,180 

31.25         59.70 

31,920 

48,050 

33.75 

71.42 

37,400 

57,320 

30.50     !     68.10 

32,185 

48,360 

36.25 

74.28 

37,260 

56,780 

30.25 

67.20 

33,880       48,400 

33.75 

73.64 

37,480 

57,420 

31.00 

66.30 

.... 

34.  15 

Av.  36,634 

57,201 

30.25 

63.94 

Av.  32,745 

48,384 

72.49 

144  THE  MATERIALS  OF  CONSTRUCTION. 

usually  goes  as  blown,  without  correction.  The  open-hearth  product  is 
therefore  under  better  control. 

5.  The  remarkable  homogeneity  of  open-hearth  steel  is  indicated  by  the 
preceding  series  of  tests  (Table  XI)  on  specimens  cut  from  different  por- 
tions of  plates  rolled  from  four  different  heats.* 

101.  Molecular  Structure  of  Wrought  Iron  and  Steel. — One  of  the  most 
important  facts  for  the  engineer  to  fix  in  his  mind  is  this:  All  grades  of  iron 
and  steel,  originally  formed  in  a  molten  state,  will  always  thereafter,  when 
cooled  after  either  a  melting,  forging,  or  rolling,  take  a  crystalline  form. 
That  is  to  say,  all  cast,  or  ingot,  metal  is  always  crystalline  whether  cast, 
hammered,  or  rolled  to  its  final  forms. f  This  includes  all  the  grades  of 
"  steel "  as  given  in  the  second  classification,  p.  89,  as  well  as  the  cast  iron 
and  cast  steel. 

It  may  also  be  said  that  wrought  iron  also  shows  a  crystalline  structure 
whenever  a  portion  of  the  iron  in  the  puddle-ball  was  in  a  liquid  condition 
when  removed  from  the  furnace.  This  liquid  iron  may  result  either  from 
the  entangling  of  unreduced  but  melted  cast  iron  in  the  glutinous  mass,  or 
from  too  high  a  temperature  of  the  furnace,  resulting  in  the  melting  down 
(burning)  of  the  reduced  metal,  or  wrought  iron  proper,  which  when 
".brought  to  nature"  and  at  the  proper  temperature  should  be  a  spongy, 
pasty  mass,  sufficiently  firm  to  be  handled  with  the  puddling -bars.  This  is 
only  a  special  case  of  ingot  metal,  since  so  much  of  the  iron  in  the  puddle- 
ball  as  comes  out  in  a  liquid  form  is,  within  itself,  free  from  the  slag  which 
covers  the  more  pasty  iron  mass,  within  and  without,  as  a  slime  might 
adhere  to  the  entire  internal  and  external  surface  of  a  sponge  which  has  been 
lifted  from  it  and  squeezed.  Any  given  portion  of  this  puddle-ball,  when 
finally  rolled  out  into  plates  and  bars,  will  become  a  small  filament  or  fibre 
of  the  cross-section,  but  greatly  extended  in  the  direction  of  the  rolling. 
Thus,  if  a  small  pocket  of  liquid  iron  was  entangled  in  the  ball,  this  would 
become  a  small  crystalline  thread  throughout  the  bar.  A  larger  mass  of 
melted  metal  would  make  a  longer  crystalline  portion,  of  the  cross-section. 

When  wrought  iron  is  properly  made,  that  is,  when  it  is  entirely  reduced 
or  "  brought  to  nature,"  and  when  the  furnace  is  not  so  hot  as  to  melt  the 
pasty  mass,  wrought  iron  will  be  found  to  be  practically  free  from  crystalline 
formations,  and  to  be  wholly  fibrous.  The  fibrous  structure  is  due  to  the 
continuous  mixture  of  the  slag  with  the  iron,  which,  after  repeated  piling  andi 
rolling,  leaves  the  slag  so  distributed  through  the  mass  in  thin  filaments  as, 
to  prevent  any  visible  crystalline  arrangement  of  the  molecules,  although! 
each  such  filament  is  really  a  series  of  distorted  (usually  elongated)  crystalline 
forms. 

*  From  H.  H.  Campbell's  paper  on  "  The  Open-hearth  Process"  before  the  World's 
Engineering  Congress.  Trans.  Am.  Inst.  Min.  Engrs.,  vol.  xxn.  p.  352. 

f  That  is  to  say,  when  shaped  while  hot.  When  shaped  cold,  as  by  cold  rolling  or 
-wire-drawing,  the  crystalline  form  may  be  partly  or  even  wholly  destroyed. 


STEEL.  145 

102.  Fracture  Showing  Structure. — In  order  to  obtain  a  normal  fracture 

of  any  malleable  metal,  or  one  which x shows  the  true  character  of  the  molec- 
ular arrangement,  uninfluenced  by  the  distorting  effects  of  the  forces  used 
to  produce  the  fracture,  it  is  common  to  nick  the  specimen  with  a  chisel  and 
bend  it.*  This,  however,  subjects  one  side  of  the  uncut  section  to  a  com- 
pression, and  the  other  to  a  tension;  and  even  if  a  fracture  is  effected,  the 
entire  surface  has  not  been  treated  alike.  It  is  better,  therefore,  to  turn  a 
sharp  groove  into  the  side  of  the  specimen  all  around  (QY  nick  it  with  a 
chisel),  and  then  to  pull  the  specimen  in  two  in  a  testing-machine.  This 
will  always  reveal  the  true  structure  of  the  metal,  without  the  distorting 
effects  accompanying  the  cold  drawing  out  (elongation)  of  the  specimen  which 
is  purposely  sought  in  the  ordinary  tensile  test.  To  insure  against  any 
elongation  whatever,  the  tool  used  must  be  perfectly  sharp  at  the  point,  so 
that  the  bottom  of  the  groove  is  a  true  angle,  and  not  a  curve  with  a  finite 
radius.  When  good  structural  steel  is  tested  in  tension  it  elongates  at  the 
ruptured  section  fully  100  per  cent;  that  is,  it  stretches  here  to  more  than 
twice  its  original  length,  and  this  cold  drawing  out  of  the  metal  wholly 
destroys  its  original  molecular  arrangement,  so  that  the  fracture  always  look 
"  fibrous  "  or  "  silky."  This  universal  appearance  of  soft  and  medium  steel 
when  pulled  in  two  leads  many  persons  to  suppose  that  this  material  has  not 
normally  a  crystalline  arrangement.  When,  therefore,  they  find  this  same 
material  broken  in  use,  as  on  a  screw-thread,  or  at  a  shoulder,  or  at  a  sudden 
reduction  of  section,  and  they  discover  it  having  a  wholly  crystalline  struc- 
ture, they  conclude  that  this  is  abnormal,  and  that  the  material  has 
"crystallized  in  service."  The  simple  test  described  above,  of  pulling  a 
grooved  specimen,  will  prove  that  all  grades  of  steel,  even  to  the  softest  ingot 
iron,  has  normally  a  crystalline  structure.  If  the  nicking  te§t  be  cited  to 
prove  this  fact,  it  is  often  claimed  that  the  nicking  produced  such  a  jarring 
of  the  metal  as  to  cause  it  to  instantly  rearrange  its  molecules,  while  cold  and 
rigid,  into  the  crystalline  form!  Surely  the  grooving  in  a  lathe  is  not  open 
to  even  this  shadowy  ground  of  suspicion.  - 

If  wrought  iron  be  grooved  and  pulled  as  here  described,  it  will  be  found 
to  be  apparently  wholly  fibrous  (if  of  a  superior  quality,  the  crystallized 
filaments  being  so  small),  or  containing  occasional  small  crystalline  patches, 
(if  of  an  ordinary  quality),  or  sometimes  nearly  wholly  and  coarsely  crystal- 
line (if  of  a  very  inferior  quality).  It  is  therefore  said  to  be  normally  of  a 
fibrous  or  non-crystalline  structure.  Now  when  wrought  iron  breaks  in 
service  and  reveals  a  coarsely  crystalline  structure,  it  simply  indicates,  in 
the  opinion  of  the  author,  the  original  poor  quality  of  the  material,  and  does 
not  prove  that  the  material  had  crystallized  in  service  as  is  generally  sup- 


*  Metcalf  affirms  that  a  skilful  workman  can  grade  steel,  by  the  fracture,  for  cus- 
tomers, so  closely  that  "year  after  year  not  one  piece  will  vary  in  carbon  more  than 
0.05  per  cent  above  or  below  the  mean  for  that  temper."  Steel,  p.  6.  This  can  only  be 
true  of  material  from  the  same  establishment  produced  under  like  conditions. 


146  THE  MATERIALS  OF  CONSTRUCTION. 

posed.     This  subject  has  been  discussed  at  considerable  length  in  Article 
93. 

103.  Structure  of  Steel  as  Affected  by  Heat  Treatment. — While  steel  or 
ingot  iron  is  entirely  free  from  slag  and  similar  foreign  ingredients,  it  must 
not  be  regarded  as  a  simple  or  single  mineral,  or  substance,  but  rather  as  a 
substance,-  like  granite,  made  up  of  a  number  *  of  separate  minerals  or 
"  metarals  "  (a  term  suggested  by  Howe),  each  crystallizing  out  by  itself, 
or  being  left  as  a  matrix  after  the  more  controlling  minerals  have  crystallized 
out.  The  particular  final  arrangement  depends  on  which  of  these  various 
proximate  combinations  control  in  the  crystallizing  stage  of  cooling,  and  also 
on  the  heat  treatment  it  receives.  Concerning  the  effect  of  the  heat  treat- 
ment on  the  appearance  of  the  fracture,  the  following  statements  are  based 
on  the  discussion  of  this  subject  by  Howe  (§§  240-250).  (See  also  Appen- 
dix A.) 

1st.  There  is  a  critical  temperature,  at  a  "  low  yellow  "  heat  (lower  for 
high-carbon  and  higher  for  low-carbon  steel),  above  which  the  material 
forms  rapidly  into  coarse  crystals. 

2d.  If  cooled  either  slowly  or  rapidly  from  above  this  temperature,  it  is 
coarsely  crystalline,  the  coarseness  of  the  crystals  depending  on  the  time 
allowance  for  their  formation  when  at  this  higher  temperature. 

3d.  If  worked  (forged  or  rolled)  in  cooling  from  this  higher  temperature, 
the  crystallization  is  that  characterizing  its  temperature  when  leaving  the 
hammer  or  rolls. 

4th.  If  raised  from  a  temperature  below  a  low  red,  just  to  this  critical 
temperature,  whatever  its  previous  condition,  or  if  worked  down  to  this 
critical  temperature  in  'cooling  from  a  higher,  and  cooled  rapidly  as  by 
quenching  in  water  or  oil,  it  is  so  finely  crystalline  as  to  appear  amorphous, 
or  porcelanic,  to  the  naked  eye.  If  cooled  slowly  from  this  critical  tempera- 
ture, it  is  finely  crystalline  to  the  naked  eye. 

5th.  Since  there  is  no  tendency  to  crystallize  below  a  low  red  heat,  it  is 
sufficient  to  cool  rapidly  from  the  critical  temperature  (low  yellow)  down  to 
a  low  red,  or  to  continue  to  work  the  metal  to  this  temperature,  after  which 
the  cooling  may  be  slow,  thus  preserving  the  porcelanic  fracture  and  obtain- 
ing a  greater  toughness. 

6th.  As  an  illustration  of  the  effects  of  these  different  treatments,  we 
have  f 

For  slow  cooling  after  forging,  size  of  grain 0.1414  in.  diam. 

Reheated  to  the  low  yellow  and  cooled  slowly,  size  of  grain  0.0048       " 
Eeheated  to  low  yellow,  quenched  in  water  to  low  red,  and 

then  slowly  cooled,  size  of  grain 0.0004       " 

*  Seven  such  having  already  been  distinguished;  see  Howe's  Metallurgy  of  Steel,  §  237. 
Osmond  has  recently  added  at  least  two  new  ones,  and  furthermore  diamond  has  now 
been  isolated  from  certain  steels.  Stahl  u,  Eisen,  vol.  xvi,  No.  15,  1896. 

f  Quoted  by  Howe,  §  250,  from  Chernoff . 


STEEL.  147 

The  size  of  this  last  is  entirely  too  small  to  be  discoverable  by  the  naked 
•eye,  and  hence  it  would  appear  amorphous  or  porcelanic. 

7th.  The  bright  surfaces  observed  on  a  steel  fracture  may  be  either 
•cleavage  planes  across  individual  crystals,  or  their  exterior  sides,  depending 
on  which  surface  offers  the  least  resistance  to  rupture.  In  either  case  the 
size  of  these  individual  surfaces  is  a  true  index  of  the  coarseness  or  fineness 
•of  the  crystalline  structure. 

8th.  The  appearance  of  a  steel  fracture  is  thus  a  good  indication  of  the 
condition  of  the  metal  when  it  left  the  rolls,  or  of  its  subsequent  treatment. 
The  student  should  himself  verify  these  statements  at  the  forge. 

This  subject  will  be  discussed  again  when  treating  of  hardening,  temper- 
ing, and  annealing.  See  Arts.  130  to  134. 

104.  The  Mechanical  dualities  of  Steel. — When  the  term  steel  is  made 
to  include  all  grades  of  ingot  metal  as  well  as  converted  wrought  iron,  its 
qualities  are  so  various  as  to  necessitate  a  series  of  trade  names,  such  as 
flange-steel  and  shell-steel,  for  boiler-plates;  tank-steel,  for  plates  of  uncer- 
tain quality  and  of  cheap  manufacture,  often  used  where  a  better  grade  is 
needed;  structural  steel,  both  mild  and  medium,  used  for  all  kinds  of 
structural  shapes,  as  angles,  I  beams,  channels,  T's,  etc. ;  rail-steel,  used 
for  railway  rails,  both  steam,  and  electric;  machinery-steel,  especially  adapted 
to  forging  and  welding;  tool-steel,  spring-steel,  saw-steel,  etc. 

The  special  qualities  required  of  these  various  grades  of  steel  are  approxi- 
mately as  follows: 

Fire-box  Steel,  Flange-steel,  and  Rivet-steel — used  for  locomotive  fire- 
boxes, boiler-heads,  rivets,  and  other  purposes  where  it  is  subject  to  great 
deformations  in  service,  or  where  it  must  be  shaped,  or  dished,  in  manufac- 
ture in  such  a  way  as  is  only  practicable  with  a  very  soft,  or  pliable,  semi-plastic 
material.  This  grade  of  steel,  therefore,  must  be  ductile  rather  than  strong, 
and  extremely  tough  and  capable  of  resisting  great  abuse,  either  cold  or  hot, 
without  losing  its  strength  or  toughness.  This  steel  has  a  tensile  strength 
of  from  50,000  to  00,000  Ibs.  per  square  inch;  an  elastic  limit*  of  from 
30,000  to  40,000  Ibrf.  per  square  inch;  an  elongation  of  from  "25  to  35  per 
cent  in  eight  inches;  a  reduction  of  area  of  from  50  to  65  per  cent  at  the 
fractured  section.  It  will  also  bend  cold  through  180,  and  close  down  per- 
fectly flat,  as  in  Fig.  71,  either  under  the  hammer  or  in  a  press,  up  to  a  thick- 
ness of  f  inch  to  1  inch  without  showing  any  sign  of  fracture.  One  could 
literally  tie  it  in  knots  while  cold,  as  in  Fig.  70  without  sign  of  rupture. 
Made  now  mostly  by  the  open-hearth  process. 

Shell-steel  is  used  for  boiler-shells,  and  for  structural  purposes,  where  a 
greater  tensile  strength  may  be  obtained  at  the  expense  of  some  ductility. 
This  steel  has  a  tensile  strength  of  from  55,000  to  05,000  Ibs.  per  square 
inch;  an  elastic  limit  of  from  33,000  to  44,000  Ibs.  per  square  inch;  an 
elongation  of  from  25  to  30  per  cent  in  eight  inches;  a  reduction  of  urea  of 


*  Here  the  commercial  elastic  limit  is  meant,  or  the  break-down  point. 


148 


THE  MATERIALS  OF  CONSTRUCTION. 


from  50  to  60  per  cent  at  the  fractured  section.      Made  by  the  open-hearth 
and  the  Bessemer  processes. 


PIG.  70.— Knot  of  Rivet-steel,  f  in.  in  diameter,  pulled  to  Incipient  Fracture  by  the 

Author. 


FIG.  71.— Flange-steel  Plates,  |  in.  thick. 

Tank-steel  has  no  particular  limits  of  quality.  It  is  a  term  which  means 
the  cheapest  grade  of  steel  plate  on  the  market;  is  sold  with  no  guarantee; 
its  qualities  usually  unknown,  or  at  least  unrevealed ;  is  likely  to  be  extremely 


STEEL.  149 

various  in  quality,  even  in  different  parts  of  the  same  plate;  and  should  be 
used  only  for  indifferent  purposes.     Made  by  the  Bessemer  process.  * 

Structural  Steel  is  used  for  bridges,  roofs,  steel  skeletons  of  buildings, 
etc.,  and  should  be  of  a  superior  quality.  Several  grades  are  recognized, 
although,  these  names  are  used  loosely,  and  have  no  precise  meaning.  Thus 
soft  and  mild  structural  steel  may  be  regarded  as  the  same  in  quality  as  the 
flange  and  shell  steel  respectively  described  above.  Medium  structural  steel 
might  be  considered  as  having  a  tensile  strength  of  from  00,000  to  70,000 
Ibs.  per  square  inch;  an  elastic  limit  of  from  35,000  to  45,000  Ibs.  per  square 
inch;  an  elongation  of  from  20  to  25  per  cent  in  eight  inches;  a  reduction 
of  area  of  from  50  to  60  per  cent  at  the  fractured  section.  Hard  structural 
steel  having  a  tensile  strength  of  from  G5,000  to  75,000  Ibs.  per  square  inch 
is  now  used  but  little,  as  it  suffers  too  much  from  shearing,  punching,  and 
assembling  to  make  it  as  reliable  as  is  desired  for  such  material.  Made  by 
"both  the  open-hearth  and  the  Bessemer  processes. 

Rail-steel  must  be  very  hard,  with  a  high  elastic  limit  to  resist  abrasion 
and  wear,  while  it  must  also  have  great  strength  and  resilience,  or  resistance 
to  shock.  It  is  a  hard  steel,  having  a  tensile  strength  of  from  70,000  to 
80,000  Ibs.  per  square  inch;  an  elastic  limit  of  from  40,000  to  50,000  Ibs. 
per  square  inch;  an  elongation  of  from  15  to  20  per  cent  in  eight  inches;  a 
reduction  of  area  of  from  40  to  50  per  cent  at  the  fractured  section.  Made 
by  the  Bessemer  process. 

Ordinary  Tool-steel,  Spring-steel,  etc.,  are  harder  grades,  capable  of  being 
hardened  and  tempered,  in  which  the  tensile  strength  and  ductility  are  of 
less  importance  than  its  hardening  qualities.  The  tensile  strength  here  may 
be  from  90,000  to  160,000  Ibs.  per  square  inch  and  the  elongation  very  smalt, 
depending  on  the  particular  temper  given  to  the  specimen.  Made  by  the 
Bessemer,  open-hearth,  and  crucible  processes. 

The  Finer  Grades  of  Tool-  and  Spring-steel,  especially  such  as  are  to  be 
used  for  edge-tools,  are  still  made  of  crucible-steel.  Metcalf  ^'"es  the  follow- 
ing tempers  for  their  respective  uses : 

"  0.50  to  0.70  C  for  hot  work  and  for  battering-tools,  and  for  tools  of 
dull  edge. 

"0.70  to  0.80  C  for  battering-tools,  cold-sets,  and  some  forms  of  reamers 
and  taps. 

"  0.80  to  0.90  C  for  cold-sets,  hand-chisels,  drills  taps,  reamers,  and 
dies 

"0.90  to  1.00  C  for  chisels,  drills,  dies  axes,  knives,  and  many  similar 
purposes. 

"1.00  to  1.10  C  for  axes,  hatchets,  knives,  large  lathe-tools,  and  many 
kinds  of  dies  and  drills  if  care  be  used  in  tempering  them. 

"1.10  to  1.50  for  lathe-tools,  graving-tools,  scribers,  scrapers,  small 
drills,  and  many  similar  purposes. 

"  The  best  all-around  tool-steel  is  found  between  0.90  and  1.10  C.  This 
can  be  adapted  safely  and  successfully  to  more  uses  than  any  other  temper." 

*  See  Plate  III  for  the  sad  effects  of  using  such  material  iu  an  important  structure. 


150  THE  MATERIALS  OF  CONSTRUCTION. 

This  is  at  and  just  above  the  point  of  complete  saturation  of  combined 
carbon. 

105.  Qualities  of  Steel  as  Affected  by  its  Chemical  Composition, — Mr. 
H.  M.  Howe,  the  highest  authority  on  this  subject,  says  (§1):  "I  conceive 
steel  to  consist  (A)  of  a  matrix  of  iron  which  is  sometimes  (as  in  ingot  iron 
and  annealed  steel),  comparatively,  or  even  quite  pure,  and  sometimes  (as  in 
hardened  steel,  manganese-steel,  etc.),  chemically  combined  with  a  portion, 
or  even  the  whole  of  the  other  elements  which  are  present,  probably  in 
indefinite  ratios,  its  mechanical  properties  being  greatly  affected  by  them;, 
and  (B)  of  a  number  of  independent  entities  which  we  may  style  '  minerals,'  * 
chemical  compounds  of  the  elements  present,  including  iron,  which  crystal- 
lize within  the  matrix,  and  by  their  mechanical  properties,  shape,  size,  and 
mode  of  distribution  also  profoundly  affect  the  mechanical  properties  of  the 
composite  mass,  though  probably  less  profoundly  than  do  changes  of  corre- 
sponding magnitude  in  the  composition  of  the  matrix." 

And  again  (§  237),  "  From  the  microscopic  study  of  polished  sections 
iron  (and  steel)  appears  to  be  constituted,  like  granite  and  similar  compound 
crystalline  rocks,  of  grains  of  several  distinct  crystalline  minerals,  of  which 
seven  common  ones  have  already  been  recognized,  through  peculiarities  of 
crystalline  form  and  habit,  color,  lustre,  hardness,  and  behavior  towards 
solvents.  Their  nature,  size,  shape,  and  orientation,  and  through  these  the 
structure  and  physical  properties  of  the  metal  as  a  whole,  seem  to  depend 
chiefly — 

1.  On  the  ultimate  chemical  composition  of  the  mass; 

2.  On  the  mechanical  treatment  which  it  has  undergone; 

3.  On  the  conditions  under  which  it  has  been  heated  and  cooled,  i.e.,, 
its  "  heat-treatment,"  which  may  induce  the  ultimate  components  of  the 
mass  to  regroup  themselves  in  new  combinations,  thus  causing  one  set  of 
minerals  to  give  place  to  another." 

When  the  iron  or  steel  is  in  a  state  of  fusion  the  ingredients  are  in  mutual 
solution,  and  they  do  not  separate  until  the  fluid  mass  congeals  or  hardens, 
when  one  or  another  of  these  mineral  ingredients  crystallizes  out  first,  and 
thus  gives  its  own  characteristics  greater  prominence  than  the  other  minerals 
which  form  the  matrix,  or  which  form  in  crystals  later,  and  subject  to  the 
limitations  as  to  form  and  size  imposed  by  the  previously  formed  crystals. 

Just  as  the  character  of  a  granite  rock,  therefore,  is  to  be  judged  from 
the  character  of -its  mineral  constituents,  as  proximate  chemical  compounds, 
and  very  imperfectly  from  ever  so  exact  a  determination  of  its  ultimate  ele< 
ments,  so  we  must  learn  to  rely  with  less  assurance  on  the  ultimate  chemica 
analysis  of  iron  and  steel,  and  more  on  the  proximate  chemical  compounds 
formed  therefrom.  Unfortunately  these  latter  are  very  difficult  of  deter 
mination,  or  even  of  identification,  and  hence  we  know  very  little  abou 
them.  It  is  for  this  reason  that  we  are  as  yet  unable  to  infer  with  any  grea 

*  But  for  which  Mr.  Howe  suggests  the  term  ' '  metarals. " 


STEEL.  151y 

assurance  the  mechanical  properties  from  the  chemical  analysis.  Such  con- 
clusions as  may  be  drawn  from  chemical  composition  are  partially  summarized 
in  the  following  articles. 

INFLUENCE   OF   CARBON   ON   IRON. 

106.  Combination  of  Carbon  with  Iron. — The  effects  of  carbon  on  iron 
are  more  pronounced  and  useful  than  those  of  any  other  known  chemical 
element.  Iron  absorbs  carbon  readily,  becoming  saturated  with  about  4.6 
per  cent  of  it,  unless  aided  by  manganese,  when  it  may  absorb  as  much  as 
7  per  cent. 

Cast  Iron  may  be  regarded  as  supersaturated  with  carbon,  or  as  having 
some  4  per  cent  of  this  element  in  some  form. 

Wrought  Iron  is  nearly  free  from  carbon  in  any  form,  having  perhaps  not 
over  0.10  per  cent. 

Steel  (ingot  metal)  may  have  anywhere  from  0.05  to  1.50  per  cent 
of  carbon,  the  upper  limit  usually  being  about  one  per  cent.  For  extreme 
hardness,  steel  may  be  made  with  as  much  as  two  or  even  three  per  cent 
carbon,  while  0.9  per  cent  C  gives  maximum  working  qualities  for  tool- 
and  spring-steels.  (This  is  the  point  of  perfect  saturation  of  combined 
carbon.) 

Three  States  of  Carbon  in  Iron. — Carbon  is  found  in  iron  in  three  rad- 
ically different  states: 

1.  Mechanically  mixed,  in  the  form  of  a  graphite,  this  being  thrown  out, 
or  excluded,  when  cast  iron  crystallizes  from  a  melted  state. 

2.  Chemically  combined  in  unknown  proportions,  this  forming  a  very 
hard  and  strong  compound,  and  the  carbon  so  combined  being  here  called 
hardening  carbon.*' 

3.  Chemically:  combined,  as  a  carbide  of  iron  (FesC),  up  to  the  satura- 
tion-point of  0.9  C.     It  is  intensely   hard  according  to  Sqrby,   though  it 
does  not  appear  to  contribute  to  the  hardness  of  steel  to  the  same  degree  as 
the  hardening  carbon,  f 

We  shall  therefore  speak  of  the  uncombiued  carbon  as  graphite  (often 
called  graphitic  carbon),  and  the  chemically  combined  carbon  as  hardening 
carbon  and  cement  carbon. 

When  the  metal  is  fused  all  the  carbon  may  be  regarded  as  chemically 
combined  in  the  form  of  hardening  carbon.  When  there  is  a  great  deal  of 
this,  as  in  cast  iron,  a  large  proportion  of  it  is  thrown  out  as  graphite  in  the 
early  stages  of  cooling,  if  sufficient,  time  be  allowed  for  this  action  to  complete 

*  Prof.  J.  O.  Arnold  (Sheffield)  gives  the  formula  Fe24C  for  this  component.  Trans. 
Inst.  Civ.  Eng.,  vol.  cxxin,  1896.  Many  authorities  agree  with  Osmond  in  attributing 
the  hardness  of  quenched  steel  to  an  allotropic  form  of  iron.  Both  sides  are  well 
presented  in  the  discussion  of  Arnold's  paper,  here  cited.  See  Appendix  A. 

f  Besides  these  diamond  has  recently  been  isolated,  and  Ledebur  -adds  "temper- 
carbon." 


152 


THE  MATERIALS  OF  CONSTRUCTION. 


itself.  When  there  is  not  over  0.9  per  cent  of  total  carbon,  none  of  it  will 
appear  as  graphite  in  the  cold  product. 

A  change  from  hardening  carbon  to  cement  carbon  occurs  (time  permit- 
ting) at  a  low  yellow  heat,  and  no  further  change  occurs  below  a  low  red 
heat. 

These  changes  and  also  the  subsequent  condition  of  the  metal  are  indi- 
cated graphically,  in  a  general  way,  in  Figs.  72  and  72a.  Thus  in  Fig.  72 
the  total  carbon  in  cast  iron  being  about  4  per  cent,  as  soon  as  it  begins  to 


FIG.  72. — Change  of  Carboii  in  Cast  Iron. 


FIG.  72a.— Change  of  Carbon  iii  Steel. 

congeal  or  crystallize,  it  begins  to  expel  carbon  in  the  form  of  graphite,  and 
this  action  is  supposed  to  be  completed  when  the  metal  has  cooled  to  TV,  at 
which  time  the  product  has  probably  become  wholly  crystalline,  having 
perhaps  less  than  one  per  cent  of  carbon  left  in  the  combined  form,  as 
hardening  carbon.  It  is  new  very  granular  in  its  nature,  having  little  or  no 
cohesion,  and  this  intermediate  granular  form  will  always  prevent  the  rolling 
of  steel  direct  from  the  melted  state.  At  the  temperature  W  (low  yellow)  a 
peculiar  change  occurs  in  the  combined  carbon,  a  large  part  of  it  passing 
from  the  hardening  to  the  cement  form,  if  sufficient  time  be  given  at  this 
temperature  for  this  to  occur.  This  change  in  the  carbon  state  is  accom- 
panied by  a  remarkable  development  of  sensible  heat,  causing  the  color  to 
brighten  up  again,  and  this  phenomenon  is  known  as  recalescence.  This 
marks  the  truly  plastic  state  at  which  it  should  be  worked.  As  shown  in 
Fig.  72a,  there  is  no  appreciable  amount  of  graphitic  carbon  in  steel,  it  all 
being  in  chemical  combination,  but  changing  from  the  hardening  to  the 
cement  form,  in  a  falling,  and  back  again  for  a  rising,  temperature  past 
the  critical  low  yellow  heat. 

The  presence  of  the  large  amount  of  graphitic  carbon  in  cast  iron  causes 
it  to  fuse  at  a  much  lower  temperature  than  steel,  because  of  the  recombin- 
ing  of  this  carbon,  chemically,  with  the  iron  at  this  high  heat.  The  fusing 
temperature  of  steel  is  higher  as  the  proportion  of  carbon  is  less. 


\ 


STEEL.  153 

107.  Physical  Effects  in  Steel  of  the  Change  in  the  Combined  Carbon  at 
a  Low  Yellow  Heat.— Hardening  and  Tempering.— This  change  in  the 
combined  carbon  of  steel  from  hardening  to  cement  and  back  again  is 
accompanied  by  a  corresponding  change  in  the  crystalline  arrangement,  in 
the  appearance  of  the  fracture,  and  in  all  its  mechanical  properties.  Thus 
if  the  region  W — V,  Fig.  73,  be  passed  quickly,  as  when  the  specimen  is 
quenched  in  water  from  a  temperature  above  TF,  there  is  very  little  change 
in  passing  this  critical  temperature,  and  hence  the  carbon  remains  mostly  in 
the  hardening  state.  This  gives  a  very  hard  and  brittle  product  (when  the 
percentage  of  carbon  is  high,  or  from  0.75  to  1.0  per  cent),  and  in  all  cases 
raises  the  elastic  limit  and  the  ultimate  strength,*  but  reduces  the  ductility. 
The  crystalline  arrangement,  also,  is  now  that  which  was  formed  on  the  first 
cooling,  above  IF,  it  being  very  coarsely  crystalline. 

If  the  region  W —  V  be  passed  slowly,  more  especially  if  the  specimen  be 
held  at  this  temperature  for  a  considerable  period  and  then  cooled  slowly,  the 
combined  carbon  changes  mostly  to  the  cement  state,  and  a  great  softening 
of  the  material  results.  The  only  way  to  retain  the  carbon  in  the  hardening 
state,  when  cold,  being  to  cool  it  quickly  from  a  temperature  above  W.\ 

When  steel  has  been  hardened  by  sudden  cooling  from  above  IF,  it  can  be 
tempered,  or  softened,  by  heating  again,  to  some  temperature  below  V  and 
cooling  slowly.  The  higher  this  tempering  heat  is,  below  a  red  heat,  followed 
by  slow  cooling  (as  in  the  air),  the  softer  will  be  the  product  when  cold,  as 
the  more  of  the  hardening  carbon  will  be  changed  to  the  cement  state.  If 
the  reheating  be  carried  to  V  or  above,  and  cooled  slowly,  the  carbon  will  be 
(almost)  wholly  in  the  cement  state,  the  temper  then  having  been  entirely 
drawn.  The  particular  temper  required,  therefore,  is  obtained  by  first 
quenching  from  TF  or  above,  then  reheating  to  the  required  temperature 
below  F,  and  cooling  slowly.  This  leaves  the  required  portion  of  the  carbon 
in  the  hardening  state,  and  gives  the  product  the  desired  compromise 
qualities  of  strength,  hardness,  and  ductility,  combined  with  toughness. 

In  the  matter  of  the  fracture,  also,  either  a  slow  or  a  rapid  cooling  from 
a  white  heat,  without  forging  or  rolling,  leaves  a  coarse  crystalline  fracture. 

If  worked  down  to  a  red  heat  it  gives  a  fine  crystalline  fracture. 

It  is  of  the  utmost  importance  that  the  heating  for  both  hardening  and 
for  tempering  should  be  uniform  throughout  the  entire  body  of  the  specimen. 
Evidently  a  liquid  bath  of  some  kind  furnishes  the  ideal  condition  for  both 
heating  and  cooling.  Thus  a  melted  lead  bath,  kept  stirred,  may  be  used 
for  heating,  and  a  mercury,  brine,  water,  or  oil  bath  for  the  quenching,  or 
sudden  cooling.  All  hardening  should  be  done  by  quenching  from  a  rising 
temperature,  to  preserve  fineness  of  grain.  The  reheating  of  the  hardened 

*  Quenching  in  water  from  a  high  temperature  may  impair  the  ultimate  strength  of 
low  carbon-steel.  Quenching  in  oil  seems  always  to  increase  the  ultimate  strength. 

f  If  not  uniformly  heated  when  quenched,  it  is  apt  to  break  or  crack  from  internal 
stress.  The  different  densities  resulting  from  quenching  from  different  temperatures, 
may  furnish  a  key  to  this  action. 


154 


THE  MATERIALS  OF  CONSTRUCTION. 


steel  for  the  purpose  of  tempering  it, may  be  done  by  holding  it  over  a  fire, 
or  in  contact  with  a  heated  mass  of  iron,  or  in  boiling  water,  or  hot  steam, 
or  in  some  other  way. 

When  clean  iron  or  steel  is  heated  in  the  open  air,  the  oxide  which  forms 
on  the  surface  takes  in  succession  the  following  well  defined  colors,  namely : 
light  straw,  straw,  light  brown,  darkey  brown,  pigeon-wing  (a  purplish 
brown),  light  blue,  dark  blue,  and  black.  In  tempering,  the  final  "  temper  " 
depends  on  which  of  these  graduated  colors  has  been  reached,  and  followed 
by  slow  cooling.  Thus  if  only  the  first  color  indication,  light  straw,  be 
reached,  and  then  the  bar  slowly  cooled,  evidently  very  little  softening  of 
the  hardened  steel  has  resulted,  and  the  product  is  left  very  hard,  or  it  is 
said  to  have  a  "  very  high  temper  ";  whereas  if  the  highest  temperature  had 
been  reached,  at  which  the  oxide  had  deepened  to  black,  and  then  the  bar 
cooled  slowly,  it  would  be  found  to  be  quite  soft,  or  the  hardness  would  have 
been  entirely  removed.  The  word  "  temper  "  then  may  have  the  following 
meanings,  according  as  it  is  used  by  the  steel-maker  or  by  the  steel-user: 


Steel-maker's  Meaning. 

Steel-user's  Meaning. 

Temper  drawn  at 

Percentage  of  Carbon. 

Temperature. 

Name_of  Color. 

Verv  hisrii 

1  50  carbon 

About  400°  F 

'  Liffht  straw  " 

Hiffh 

1.00  to  1.20  C 

450°  F 

*  Straw  " 

Medium  

.70  to    .80  C 

500°  F. 

'  Brown  "to 

Mild 

40  to     60  C 

550°  F. 

"pigeon-wiug" 
'  Liglit  blue  " 

Low  

20  to    .30  C 

600°  F 

'  Dark  blue  " 

Soft,  or  dead  soft  

Under  .20  C 

'      650°  F. 

•Black" 

EFFECTS   OF   CARBON    IN   ITS     VARIOUS    STATES   ON    THE    MECHANICAL    PROP- 
ERTIES  OF   IRON    AND    STEEL. 

108.  Not  Fully  Explained  by  Chemical  Analyses. — As  shown  in  Art.  105. 
the  mechanical  properties  of  iron  and  steel  are  not  fully  indicated  by  anj 
ultimate  chemical  analysis  of  the  material,  bat  are  dependent  on  the  pap 
ticular  combinations  the  elements  may  have  formed.     In  Art.  106  it  wa& 
further  shown  that  carbon  is  found  in  three  distinct  forms  in  iron  and  steel, 
and  that  the  physical  qualities  depend  largely  on  these  particular  forms  o 
carbon.     It  is  to  be  expected,  therefore,  that  the  mechanical  qualities,  o 
the  qualities  shown  by  the  material  when  resisting  the  action  of  externa, 
forces,  would  also  be  found  to  be  greatly  dependent  on  these  particular  form 
of  carbon,  combined  and  uncombined,  or  even  on  the  total  combined  carbon 
since  this  has  been  shown  to  exist  in  two  very  different  states.     The  effort 
therefore,  of  students  of  this  subject  to  harmonize  the  results  of  mechanica 
tests  with  the  corresponding  ultimate  chemical  analyses  of  the  materials  wa 
foredoomed  to  failure.     And  since  the  proximate  chemical  analysis  is  as  ye 
impossible,  we   are  wholly  unable  to   predict   mechanical  properties  froc 


STEEL.  ]  55 

chemical  analysis  alone.  When  this  is  supplemented,  however,  with  a  full 
knowledge  of  the  heat  treatment,  as  described  in  the  preceding  article,  some 
approximate  knowledge  of  the  mechanical  properties  is  obtained.  (See  also 
Appendix  B. 

109.   The   Hardening  of  Steel. — A   coarsely  crystallized   steel   may   be 
reheated  to  a  temperature  between  Fand  IF,  and  cooled  either  slowly ^.or_ 
rapidly,  and  the  fracture  becomes  finely  crystalline  or  even  porcelanic.    (Jffli^t 
what  does  occur  in  the  hardening  of  high  carbon  steel  is,  and  has  long  Aceri// 
a  matter  of  contention  among  our  most  distinguished  metallurgical  chemist^ , 
Osmond  and  his  school  contend  for  an  allotropic  form  of  iron  (called  "  /? 
iron,"  to  distinguish  it  from  the  annealed  form,  which  he  called  "  a  iron  "), 
not  to  be  explained  by  a  definite  chemical  compound,  but  containing  carbon 
in  solution,  while  Prof.  Arnold  makes  a  very  strong  plea  for  a  chemical 
compound,  Fe24C,  which  he  calls  a  "  sub-carbide  "  (Fe3C  being  the  carbide), 
this  being  he  thinks  the  real  composition  of  steel  in  a  melted  state,  having 
as  much  as  0.89  per  cent  C,  which  he  calls  the  point  of  saturation.*     When 
this  compound  is  cooled  suddenly,  this  unstable  sub-carbide  hardens  into  a 
solid  without  any  change  in  its  chemical   composition;   but  when  cooled 
slowly,  it  passes  at  400°  C.  into  the  carbide  form,  with  pure  iron  (Fe2lC  = 
Fe3C  -f-  21  Fe)  and  with  the  evolution  of  heat.     See  Plates  in  Appendix  B. 

Prof.  Arnold  gives,  as  a  general  summary  of  his  views,  the  following  :f 

I.  The  constituents  of  steel  may  be:  (a)  Crystals  of  pure  iron  which  remain 
bright  on  etching,     (b)  Crystals  of  slightly  impure  iron  which  become  pale  brown 
on  etching,  probably  owing  to  the  presence  of  a  small  quantity  of  an  intermediate 
carbide  of  hypothetical  formula  FeioC.     (c)  Normal  carbide  of  iron,  FesC,  which 
exists  in   three  distinct  modifications,  each  one  conferring  upon  the  iron  in  which 
it  is  found  particular  mechanical  properties.     (1)  Emulsified  carbide  present  in  an 
excessively  fine  state  of  division  in  tempered  steels.     (2)  Diffused  carbide  of  iron 
occurring   in  normal  steels  in  the  forms  of  small  ill-defined  striae  and  granules. 
(3)  Crystallized  carbide  of  iron  occurring  as  well-defined  laminae  in  annealed  and 
in  some  normal  steels,     (d)   Subcarbide  of  iron,  a  compound  of  great  hardness 
existing  in  hardened  and  tempered  steels  and  possessing  the  formuja  Fe24C.     This 
substance  is  decomposed  by  the  most  dilute  acids,  and  at  400°  C.  it  is  decomposed 
into  Fe3C  and  free  iron  with  evolution  of  heat.     One  of  the  most  remarkable  prop- 
erties of  this  compound  is  its  capacity  for  permanent  magnetism,      (e)  Graphite 
or  "l  temper-carbon.":}: 

The  existence  of  Fe24C  is  proved  by  the  fact  that  iron  containing  0.89  per  cent 
carbon  presents  several  correlative  critical  points  when  examined  by  different 
methods  of  observation  :  (1)  Well-marked  saturation-points  in  the  micro-structure 
of  normal  annealed  and  hardened  steels.  (2)  A  sharp  maximum  in  a  curve  the 
coordinates  of  which  are  heat  evolved  or  absorbed  in  recalescence  and 'carbon  per- 
centage. (3)  A  point  in  the  compression  curve  of  hardened  steels  at  which  molec- 
ular flow  absolutely  ceases.  (4)  A  sharp  maximum  in  a  curve  the  coordinates  of 
which  are  carbon  percentage  and  permanent  magnetism  in  hardened  steels. 

II.  The  influence  of  annealing  is— (1)  To  increase  the  size  of  crystals  and  to 
increase  the  intercrystalline  cohesion  when  originally  feeble  or  impaired.     (2)  To 
convert  elongated  masses  of  iron  containing  diffused  Fe3C  into  compact  rounder 

*  With  as  much  as  1  per  cent,  manganese  he  claims  the  point  of  saturation  with  carbon 
is  reached  with  0.65  C.  See  Appendix  B. 

\  Trans,  hist.  Civ.  Engrs.,  vol.  cxxiu,  1896,  p.  160.     See  also  Appendix  B. 
\.  Ledebur  distinguishes  between  graphite  and  temper-carbon. 


THE  MATERIALS  OF  CONSTRUCTION. 


bodies,  containing  laminae  of  crystallized  Fe3C,  between  which  the  iron  becomes 
more  or  less  dovetailed  throughout  the  mass. 

III.  The  approximate  theoretical  constituents  of  hardened  and  normal  steels  will 
be  in  accordance  with  the  figures  given  in  Table  IX.  (These  percentages,  however, 
can  never  be  quite  correct,  because  in  practice  hardened  steels  below  the  saturation- 
point  (0.89$  C)  always  contain  a  little  Fe3C,  and  normal  steels  below  the  saturation- 
point  a  small  quantity  of  the  intermediate  carbide,  FeioC(?)  ).  It  is  obvious  that  in 
tempered  steels  an  almost  unlimited  variety  of  constitutions  and  consequently  of 
mechanical  properties  is  possible. 

TABLE  IX. — APPROXIMATE  THEORETICAL  COMPOSITION  OF  HARDENED  AND 
NORMAL  IRON  AND  CARBON  STEELS  REQUIRED  BY  THE  SUBCARBIDE 
THEORY  HEREIN  ENUNCIATED. 


Hardened  Steels. 

Normal  Steels. 

Carbon 

Fe. 

Fe24C. 

Fe3C. 

Fe. 

Fe,C. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent 

Per  cent. 

0.10 

89 

11 

0 

99 

1 

0.20 

78 

22 

0 

97 

3 

0.30 

67 

33 

0 

95 

.     5 

0.40 

56 

44 

0 

94 

6 

0.50 

45 

55 

0 

93 

7 

0.60 

34 

66 

0 

91 

9 

0.70 

22 

78 

0 

90 

10 

0.80 

11 

89 

0 

88 

12 

0.90 

0 

100 

0 

87 

13 

1.00 

0 

99 

1 

85 

15 

1.10- 

0 

97 

3 

84 

16 

1.20 

0 

95 

5 

82 

18 

1.30 

0 

93 

7 

81 

19 

1.40 

0 

91 

9 

79 

21 

1.50 

0 

89 

11 

77 

23 

IV.  The  snbcarbidc  theory  falls  into  line  with  the  observations  of  e very-day 
experience.  For  instance,  the  fact  has  long  been  known  that  pure  carbon  steel,  con- 
taining about  0.85  per  cent  of  carbon,  is  the  most  suitable  for  steel  which  must  carry 
a  cutting  edge  and  yet  be  tough  enough  to  withstand  a  sudden  shock.  Such  steel  is 
therefore  employed  for  cold  sets.*  It  is  also  well  known  that  a  steel  containing  1.3 
per  cent  of  carbon  would  be  useless  for  such  a  purpose,  as  it  would  crack  and 
"snip."  The  reason  is  clear;  such  material  is  full  of  lines  of  weakness  along  the 
junctions  of  the  subcarbide  granules  with  the  surplus  normal  carbide  membranes. 
On  the  other  hand,  it  is  known  that 'a  steel  harder  than  one  carrying  0.9  per  cent  of 
carbon  is  necessary  for  turning-tools.  In  such  a  case  no  shock  has  to  be  encountered, 
so  that  the  surplus  Fe3C  augments  the  hardness  of  the  subcarbide  with  its  own 
intense  hardness,  and  moreover  adds  10  per.  cent  of  a  substance  incapable  of 
"letting  down"  with  the  heat  of  friction.  It  is  also  clear  that  a  steel  with  carbon 
much  below  0.9  per  cent  cannot  carry  a  cutting  edge,  because  of  the  presence  of 
particles  of  soft  free  iron  amongst  the  mass  of  the  hard  subcarbide.  See  App.  B. 

110.  Effect  on  Tensile  Strength. — While  a  diagram  showing  the  relation 
of  tensile  strength  to  percentage  of  carbon  in  steel  gives  a  cloud  of  results 
spread  over  a  wide  belt  (see  Howe's  Metallurgy  of  Steel,  p.  14),  yet  a 
simple  formula  which  is  the  algebraic  expression  of  a  line  which  traverses 
this  field  well  below  its  centre  of  gravity  may  be  of  some  use.  While  many 

*  As  required  iu  saws. 


STEEL. 


157 


such  formulas  have  been  proposed,  that  of  Salom  *  seems  best  to  fit  the 
total  assemblage  of  results  and  is  easily  remembered.     It  is 

T—  45,000  +  100,000(7, (1) 

where    T  —  tensile  strength    of   rolled  steel  in   pounds   per   square   inch 

(up  to  C  =  1.0  per  cent); 
C  =  percentage  of  carbon 

The  recorded  tests  show  many  results  as  much  as  20,000  pounds  per 
square  inch  above  this  locus,  and  some  10,000  pounds  below  it.  It  may  be 
regarded,  therefore,  as  traversing  the  lower  edge  of  the  middle  third  of  the 
cloud  of  recorded  observations.  As  the  maximum  strength  of  steel  is 
reached  with  C  =  about  1.0  per  cent,  the  above  formula  must  not  be  used 
above  T  =  145,000  and  C  —  1.0.  Higher  values  of  tensile  strength,  as  with 
drawn  steel  wire,  are  due  to  the  physical  treatment  and  not  to  the  chemical 
composition.  The  elastic  limit  in  both  tension  and  compression  may  be 
taken  as  GO  per  cent  of  the  tensile  strength. 

As  a  result  of  a  careful  study  of  over  four  hundred  tests  accompanied  by 
their  corresponding  chemical  analyses,  made  in  the  regular  course  of  business, 
Mr.  William  E.  Webster  f  offers  the  following  table,  showing  the  variation 
of  strength  of  soft  steel  with  varying  percentages  of  carbon  and  phos- 
phorus, assuming  the  manganese  and  sulphur  are  each  zero.  When  either 
or  both  of  these  latter  are  present,  the  values  may  be  corrected  by  adding 
the  values  given  in  the  two  auxiliary  tables  for  the  corresponding  percent- 
ages of  these  ingredients. 

TABLE     XII. — ESTIMATED     ULTIMATE     STRENGTH     OF     STEEL     FOR     VARYING 

PERCENTAGES     OF     CARBON     AND     PHOSPHORUS.  \ 

On  the  assumption  that  neither  manganese  nor  sulphur  is  present,  the  tabular  values  to  be 
increased  for  these  ingredients  by  the  amounts  given  in  the  two  following  auxiliary  tables. 


Carbon  in  Parts 
of  1  per  cent. 

.06 

.08 

.10 

.13 

.14 

.16 

.18 

.26 

.22 

.24 

Percentage  of 

Phos.  .000 

39,550 

41,150 

42,750 

44,350 

45.950 

47.550 

49.150 

50,750 

52,350 

53,950 

"       .01 

40,350 

41.950 

43,750 

45,550 

47.350 

49,050 

50,650 

52,250 

53,850 

55,450 

u       .02 

41.150 

42.750 

44,750 

46,750 

48,7f>0 

50,550 

52,150 

53,750 

55.350 

•  5(5.950 

"       .03 

41.950 

43,550 

45,750 

47,950 

50.150 

52.050 

53,850 

55,250 

56.850 

58.450 

"       .04 

43,750 

44.350 

46.750 

49.150  !    51,550 

53.550 

55,150 

56,750 

58,350 

59  950 

"       .05 

43.550 

45,150 

47,750 

50.3:,0 

52.950 

55,050 

56,650 

58,250 

59,850 

61,450 

"       .06 

44,350 

45,950 

48,750 

51.550 

54,350 

56  550 

58,150 

59.750 

61,350 

62,950 

"       .07 

45.150 

46,750 

49,750 

52.750 

55,750 

58.050 

59,6:,0 

61,250 

62,850 

64,450 

"       .08 

45.950 

47,550 

50,750 

53.950 

57.150 

59.550 

61,150 

62.750 

64,350 

65  950 

"       .09 

46,750 

48.350 

51.750 

55.150 

58,550 

61,050 

62,650 

64,250 

65,850 

67,450 

"       .10 

47,550 

49,150 

52,750 

56,350 

59,950 

62.550 

64,150 

65,750 

67,350 

68,950 

.001  Phos.  = 

SO  Ibs. 

80  Ibs. 

100  Ibs. 

120  Ibs.    140  Ibs. 

150  Ibs. 

150  Ibs. 

150  Ibs. 

150  Ibs. 

150  Ibs 

*See   Trans.   Am.   Inst.   Mm.    Engrs.,   xiv.   p.    127,    and    also  Howe's    work  aa 
quoted  above. 

f  Trans.  Am.  InsL  Mm.  Engrs.,  vol.  xxm.  p.  114. 

J  Campbell  gives,  iu  his  work  on  Structural  Steel,  p.  306. 

Ultimate  strength  of  acid  steel  =  33,000  +  1485  (7+  1260  P, 
"  basic  "      =40,000  f  1085  C+  1200  P. 
\vher<j  C  =  percentage  of  carbon     and     P  —  percentage  of  phosphorus. 


158  THE  MATERIALS  OF  CONSTRUCTION. 

TABLE     XIII. — ADDITIONS     FOR     SULPHUR     IN     PARTS    OF 
ONE     PER     CENT. 

Sulphur 0      .01      .02       .03       .04       .05       .06       .07 

Additions  in  pounds  per  square  inch.. 000    500    1000    1500    2000    2500    3000    3500 

TABLE     XIV. — ADDITIONS     FOR    MANGANESE     IN     PARTS     OF 
ONE    PER     CENT. 


Man. 

Lbs. 

Man. 

Lbs. 

Man. 

Lbs. 

Man. 

Lbs. 

Man. 

Lbs. 

.15 

3,600 

.27 

6,300 

.38 

8,280 

.49 

9,780 

.60 

10,900 

.16 

3,840 

.28 

6,500 

.39 

8,440 

.50 

9,900 

.61 

11,000 

.17 

4,080 

.29 

6,700 

.40 

8,600 

.51 

10,000 

.62 

11,100 

.18 

4,320 

.30 

6,900 

.41 

8,740 

.52 

10,100 

.63 

11,200 

.19 

4,560 

.31 

7,080 

.42 

8,880 

.53 

10,200 

.64 

11,300 

.20 

4,800 

.32         7,260 

.43 

9,020 

.54 

10,300 

.65 

11,400 

.21 

5,020 

.33         7,440 

.44 

9,160 

.55 

10,400 

.66 

11,500 

.22 

5,240 

.34 

7,620 

.45 

9,300 

.56 

10,500 

.67 

11,600 

.23 

5,460 

.35 

7,800 

.46 

9,420 

.57 

10,600 

.68 

11,700 

.24 

5,680 

.36 

7,960 

.47 

9,540 

.58 

10,700 

.69 

11,800 

.25 

5,900 

.37 

8,120 

.48 

9,660 

.59 

10,800 

.70 

11,900 

.26 

6,100 

111.  Effect  on  Ductility.  —  In  general  the  ductility  of  steel  diminishes  as 
the  percentage  of  carbon  increases.  The  ductility  is  usually  determined  by 
dividing  the  total  stretch  of  a  specimen  between  marks  eight  inches  apart, 
which  includes  the  section  of  rapture,  by  the  original  length  of  eight  inches. 
This  total  stretch  is  found  after  the  specimen  has  been  broken  in  tension, 
and  is  called  the  "  percentage  of  elongation."  From  the  plotted  results  of 
over  one  thousand  determinations  of  elongation  with  known  percentages  of 
carbon,*  the  author  of  this  work  would  express  this  general  relation  by  the 
formula 


where  E  =  percentage  of  elongation  in  eight  inches, 

C  '  =  percentage  of  carbon  (less  than  1.00). 

This  would  seem  to  give  too  low  a  percentage  of  elongation  by  about  5 
per  cent  for  carbon  from  0.25  to  0.45  per  cent.  In  any  case  the  elongation 
may  vary  from  the  mean  as  given  by  this  equation  by  at  least  one  fourth  of 
its  value,  showing  that  the  ductility  is  dependent  on  other  things  besides  the 
proportion  of  carbon. 

There  seems  to  be  no  difference  between  open-hearth  and  Bessemer  steel 
in  this  respect,  but  crucible  steel  gives  an  elongation  equal  to  that  of  the 
other  varieties  of  a  lower  carburization.  In  other  words,  crucible  steel  is 
more  ductile  than  the  cheaper  grades,  for  the  same  proportion  of  carbon. 


*  Howe's  Metallurgy  of  Steel,  p.  16. 


STEEL. 


159 


112.  Elongation  and  Tensile  Strength. — Mr.  Howe  gives  a  table  of  the 
common  greatest  and  least  limits  of  elongation  for  various  grades  of  steel, 
which  have  been  plotted  in  Fig.  73.  The  shaded  area  between  these  limits 
may  be  regarded  as  the  Elongation  Field.  In  this  field  has  been  drawn  two 
curves,  which  are  the  loci  of  two  equations  expressing  elongation  in  terms  of 
the  ultimate  strength.  One  of  these  (a)  has  been  proposer!  by  a  committee 
of  the  Am.  Soc.  Civ.  Engrs.  (July,  1890),  and  the  other  (b)  by  the  author. 

JW000 


/O  20  30         40 

FIG.  73. — Showing  the  Elongation  Field  for  Structural  Steel  and  the  jjoci  of  Proposed 
Elongation  Equations.  Limits  of  Greatest  and  Least  Elongations  taken  from 
Howe's  Metallurgy  of  Steel. 

The  former  is  an  equilateral  hyperbola,  making  the  product  of  the  ultimate 
strength  per  square  inch  and  the  percentage  of  elongation  a  constant,  and 
equal  to  1,500,000,  or 


The  other  is  also  a  hyperbola  referred  to  asymptotes  parallel  to  the  main 
axes,  but  removed  from  them,  as  shown  in  the  figure,  and  whose  equation  is 


/-  10,000 


<*) 


1.60  THE  MATERIALS  OF  CONSTRUCTION. 

113.  Modulus  of  Elasticity. — As  stated  in  Art.  11,  the  modulus  of  elas- 
ticity is  not  appreciably  affected  by  the  percentage  of  carbon  or  by  any  other 
ingredient.     This  is  also  shown  by  Fig.  294.     The  author  of  this  work  be- 
lieves that  with  such  determinations  of    this  modulus  as   have  been   made 
hitherto,  it  is  rather  to  be  presumed  that  discrepant  values  are  due  to  inade- 
quate  or   erroneous   methods  of  determination  rather  than  to  actual  wide 
departures  of  the  modulus  from  its  mean  value. 

114.  The  Compressive  Strength. — The  elastic  limit  is  the  real  ultimate 
compressive  resistance   with  the  softer  grades  of  steel,  having  a   definite 
"  yield-point  "  (see  Fig.  294),  while  with  hard  steel  there  is  no  yield-point 
and  no  very  definite  elastic  limit,  and  the  ultimate  strength  in  compression 
is  clearly  marked  by  a  decided  rupture  on  planes  of  maximum  shearing  stress. 
Few  tests  of  steel  have  been  made  in  compression,  but  it  is  shown  in  Chap. 
XXVI.  that  the  compressive   elastic  limit  is  numerically  equal  to  that  in 
tension,  or  as  CO  per  cent  of  the  ultimate  tensile  strength.     In  other  words, 
the  compressive  resistance  of  steel  is  increased  by  increasing  carbon  the  same 
as  the  tensile  strength. 

115.  Hardness  and  Fusibility. — The  hardness  increases  with  increasing 
carbon  apparently  without  limit. 

The  fusibility  also  increases  with  increasing  carbon  without  limit.  Thus 
cast  iron  and  the  hard  grades  of  steel  melt  at  a  much  lower  temperature  than 
wrought  iron  and  the  soft  steels. 

INFLUENCE    OF   SILICON    ON   IRON   AND    STEEL. 

116.  Combination  of  Iron  and  Silicon. — "  Silicon  alloys  with  iron  in  all 
ratios,  at  least  up  to  30  per  cent,  being  readily  reduced  from  silica  (SiOa)  by 
carbon  in  the  presence  of  iron.     It  rarely,   if  ever,  exists  in  iron  in  the 
graphitoidal  state.     It  diminishes  the  power  of  iron  to  combine  with  carbon, 
not  only  when  molten  (thus  diminishing  the  total  carbon  content),  but  more 
especially  at  a  white  heat,  thus  favoring  the  formation  of  graphite  during 
slow  cooling.     It  increases  the  fusibility  and  fluidity  of  iron;  it  lessens  the 
formation  of  blow-holes;  by  reducing  iron  oxide  it  apparently  removes  one 
cause  of  red-shortness;  it  hinders  at  high  temperatures  the  oxidation  of  iron, 
and  probably  of  the  elements  combined  with  it.     Silicon  steels  with  1  to  2 
or  even  2.5  per  cent  silicon,  sometimes  excellent  for  cutting  hard  steel,  have 
been  made.     Iron  absorbs  silicon  greedily,  uniting  with  it  in  all  proportions, 
at  least  up  to  30  per  cent,  and  apparently  the  more  readily  the  higher  the 
temperature,  absorbing  it  even  at  a  red  heat  when  imbedded  in  sand  and 
charcoal.     Though  silica  can  neither  be  reduced  by  iron  alone  nor  by  carbon 
alone,  it  is  readily  reduced  by  carbon  if  iron  be  present  to  alloy  with  the 
resulting  silicon. 

"  Silicon  may  be  oxidized  by  both  carbonic  acid  and  carbonic  oxide:  it  is 
removed  from  molten  iron  very  rapidly  by  atmospheric  air,  and  by  simple 
contact  with  iron  oxide,  magnesia,  and  other  bases."  * 

*  Howe,  vol.  i.  p.  36. 


STEEL. 


161 


117.  Influence  of  Silicon  on  Physical  Properties. — The  effect  of  silicon 
is  to  increase  the  strength  and  to  reduce  the  ductility  of  steel,  as  shown  in 


/0QOOO 


80000 


0 


: :  :;••  i 


\   - 


40 


20 


/  2  J  4  S 

FIG.  74. — Physical   Proper  ^es  of   Silicon   Stee.,  showing   the   Effects   of   Carbon  and 
Silicon.     (Hadfield  in  Jour.  Ir.  &  St.  Inst.,  vol.  n.  p.  222.) 

Fig.  74.  It  also  has  a  decided  effect  in  increasing  the  soundness  of  ingots 
and  other  castings,  thus  preventing  blow-holes,  and  by  reducing  the  iron 
oxide  it  to  that  extent  prevents  red-shortness. 

118.  Effects  on  Cast   Iron. — The   effect  of   silicon  on  cast  iron  is   to 
increase  its  fluidity,  and  to  change  the  carbon  to  the  graphitic  form.     Thus 
hard  white  cast  iron  is  reduced  to  soft  gray  iron  by  the  addition  of  silicon, 
while  its  tensile  strength  and  its  ductility  or  toughness  is  increased. 

INFLUENCE   <XF  MANGANESE   ON   IRON   AND   STEEL. 

119.  In  General. — "  Manganese  alloys  with   iron  in   all  ratios,   being 
reduced  from  its  .oxides  by  carbon  at  a  white  heat,  and  the  more  readily  the 
more  metallic  iron  is  present  to  combine  with  it.     It  is  easily  removed  from 
iron  by  oxidation,  being  oxidized  even  by  silica,  and  partly  in  this  way, 
partly  in  others,  it  restrains  the  oxidation  of  the  iron,  while  sometimes 
restraining,  sometimes  permitting,  the  oxidation  of  the  other  elements  com- 
bined with  it.     It  is  also  apparently  removed  from  iron  by  volatilization. 
Its  presence  increases  the. power  of  carbon  to  combine  with  iron  at  very  high 
temperatures  (say  1400°  C.),  and  restrains  its  separation  as  graphite  at  lower 
ones.*     By  preventing  ebullition  during  solidification  and  the  formation  of 


*  Prof.  J.  O.  Arnold  says  that  with  1  per  cent  manganese  iron  becomes  saturated 
with  0.65  C,  instead  of  0.89  C  with  no  manganese.  Hence  the  softer  qualities  of  Swed- 
ish steels  of  a  given  percentage  of  C,  as  they  contain  only  about  0.25  -per  cent  Mn, 
See  Appendix  B. 


162 


THE  MATERIALS  OF  CONSTRUCTION. 


blow-holes;  by  reducing  or  removing  oxide  and  silicate  of  iron;  by  bodily 
removing  sulphur  from  cast  iron  and  probably  from  steel;  by  counteracting 
the  effects  of  the  sulphur  which  remains,  as  well  as  of  iron  oxide,  phosphorus, 
copper,  silica  and  silicates,  and  perhaps  in  other  ways, — it  prevents  hot- 
shortness,  both  red  and  yellow.  (It  does  not,  however,  counteract  the  cold- 
shortness  caused  by  phosphorus.)  These  effects  are  so  valuable  that  it  is 
to-day  well-nigh  indispensable,  though  admirable  steel  was  made  before  its 
use  was  introduced. 

"It  is  thought  to  increase  hardness  proper  and  fluidity,  to  raise  the 
elastic  limit  and  the  ultimate  strength,  and,  at  least  when  present  in  con- 
siderable quantity,  to  diminish  fusibility."  * 

120.  Effect  of  Small  Percentages  of  Manganeee  on  Static  Strength. — 
From  over  400  tests  of  the  strength  of  mild  steel  accompanied  by  chemical 
analyses,  Mr.  William  II.  Webster  f  estimates  the  effect  of  manganese  in 
increasing  the  ultimate  strength,  as  given  in  the  following  table : 

TABLE    XV. — INCREASE    IX    ULTIMATE  STRENGTH  FROM  SMALL  PERCENTAGES 

OF    MANGANESE. 


Manganese, 

Per  Cent. 

Increase  in  Ultimate 
Strength. 

Total  Increase  in  Ultimate 
Strength  from  0  Manganese. 

From 

To 

Libs,  per  Sq.  In. 

Lbs.  per  Sq.  In   * 

9.00 

0.15 

3,600 

3,600 

0.15 

0.20 

1,200 

4,800 

0.20 

0.25 

1,100 

5,900 

0.25 

0.30 

1,000 

6,900 

0.30 

0.35 

900 

7,800 

0.35 

0.40 

800 

8,600 

0.40 

0.45 

700 

9,300 

0.45 

0.50 

600 

9.900 

0.50 

0.55 

500 

10,400 

0.55 

0.60 

500 

10,900 

0.60 

0.65 

500 

11,400 

121.  Manganese-steel. — "  While  the  small  amounts  of  manganese  in 
ordinary  commercial  steel  increase  its  forgeableness,  and  within  certain  limits 
its  brittleness,  yet  when  so  much  manganese  is  present  that  its  effects  out- 
weigh those  of  carbon,  and  thus  forms  a  true  manganese  steel,  the  alloy 
becomes  extraordinarily  tough  and  difficultly  forgeable :  it  possesses  a  com- 
bination of  hardness  and  toughness  which  should  be  of  value  for  tools  which 
cut  by  impact,  and  which  is  not  otherwise  attainable,  so  far  as  I  know,  at 
least  in  any  material  available  for  the  arts.  Several  attempts  to  utilize  its 
remarkable  properties  have  been  made  of  late,  and  others  are  to  be 
expected."  J 

"  Briefly,  manganese-steel  of  the  best  composition,  with  say  14  per  cent 

*  Howe,  vol.  i.  p.  42. 

f  See  Trans.  Am.  Inst.  Mining  Engineers,  vol.  xxm.  p.  114. 

t  Howe,  vol.  i.  p.  48. 


STEEL.  163 

of  manganese  and  not  more  than  1  per  cent  of  carbon,  is  very  fluid ; 
solidifies  rapidly  and  with  great  contraction;  does  not  form  blow-holes,  but 
pipes  deeply ;  does  not  seem  subject  to  segregation ;  is  forgeable,  but  welds 
poorly  if  at  all.  Naturally  brittle,  only  moderately  strong,  and  with  very 
low  elastic  limit,  it  is  made  extremely  tough  and  very  strong*  and  (under 
impact)  stiff  by  quenching  from  whiteness,  which  neither  cracks  small  bars 
of  it,  changes  its  fracture  (which  before  forging  is  strongly  crystalline),  nor 
greatly  raises  its  elastic  limit;  this,  however,  is  greatly  raised  by  cold  stretch- 
ing, only  to  fall  on  reheating.  Test-bars  stretch  nearly  uniformly,  like 
brass,  instead  of  necking  like  iron.  It  is  so  hard  that  it  can  barely  be 
machined,  but  it  is  slightly  softened  by  sadden  cooling  from  very  dull  red- 
ness; is  not  brittle  at  blueness,  nor  (apparently)  made  brittle  by  blue-work, 
but  is  rapidly  made  brittle  by  cold-work,  ductility  being  restored  by  reheat- 
ing and' quenching;  does  not  recalesce  f  during  cooling;  its  density  (sp. 
gr.  7.83,  for  manganese  13.75),  modulus  of  elasticity,  and  (apparently)  its 
rate  of  corrosion  are  about  the  same  as  those  of  common  iron;  its  electric 
resistance  is  enormous,  thirty  times  that  of  copper  and  eight  times  that  of 
wrought  iron,  but  thrice  as  constant  with  varying  temperature  as  that  of 
iron;  it  can  be  magnetized  very  considerably  temporarily,  but  only  with  most 
extreme  difficulty,  and  hardly  at  all  permanently."  J 

INFLUENCE    OF   SULPHITE   ON   IRON   AND   STEEL. 

122.  In  General. — "  Sulphur  unites  with  iron  probably  in  all  proportions 
up  to  53.3  per  cent,  being  readily  absorbed  from  many  sources.     It  may, 
however,  be  prevented  from  combining  with  iron,  and  even  expelled  from  it 
by  many  agents  (e.g.,  basic  slags,  carbon,  silicon,  manganese,  oxygen,  water, 
ferric  oxide).     Certain  of  these  in  the  blast-furnace  prevent  the  sulphur 
present  from  combining  with  the  cast  iron,  and  in  the  conversion  of  pig  iron 
into  malleable  iron,  whether  by  puddling,  by  pig-washing,  or  by  the  basic 
process,  much  of  the  sulphur  of  the  cast  iron  is  expelled.     It 'causes  cast  iron 
to  retain  its  carbon  in  the  combined  state.     Carbon  and  sulphur  and  perhaps 
also  silicon  and   sulphur   are  mutually  exclusive  within  limits.     Sulphur 
makes  malleable  iron  red-short  and  interferes  with  its  welding,  but  these 
effects  are  largely  effaced  by  the  presence  of  manganese.     It  is  thought  to 
make  cast  iron  harder,  though  this  effect  is  at  least  in  part  due  to  its  causing 
it  to  retain  the  carbon  in  the  combined  state.     It  increases  the  fusibility  of 
cast  iron,  but  makes  it  thick  and  sluggish  when  molten,  and  gives  rise  to 
blow-holes  during  its  solidification."  § 

123.  Red-shortness. — "  Sulphur  has  the  specific  effect  of  making  iron 
exceedingly  brittle  at  a  red  heat,  and  of  destroying  its  welding  power.     Its 

*  Tensile  strength  raised  from  80,000  to  100,000  Ibs.  per  square  inch,  and  elongation 
in  8  inches  raised  from  two  per  cent  to  forty-five  per  cent! 
\  See  Art.  130,  (c),  for  definition  of  this  term. 
\  Howe,  vol.  i.  p.  361. 
§  Howe,  p.  48. 


164  THE  MATERIALS  OF  CONSTRUCTION. 

effect  are  in  general  most  marked  at  a  dull-red  heat,  and  irons  which  crack 
at  this  temperature  owing  to  the  presence  of  a  small  percentage  of  sulphur, 
may  often  be  readily  forged  at  higher  temperatures,  while  when  cold  they 
are  as  malleable  and  indeed  often  more  malleable,  than  non-sulphurous  irons. 
If,  however,  the  percentage  of  sulphur  is  considerable,  the  iron  is  no  longer 
malleable  even  at  temperatures  above  redness.  The  red-shortness  imparted 
by  a  given  percentage  of  sulphur  is  probably  independent  of  the  percentage 
of  carbon  which  accompanies  it;  but  more  sulphur  can  usually  be  tolerated 
in  steel  rich  in  carbon  than  in  others,  because  such  steel  usually  contains 
much  manganese  also. 

"  The  rail-steel  of  our  Eastern  mills  has  usually  from  0.03  to  0.06  per 
cent  sulphur;  that  of  our  Western  mills  has  usually  somewhat  more,  occa- 
sionally as  much  as  0.10  or  0.12  per  cent,  and  even  exceptionally  0.14  per 
cent.  When  sulphur  is  under  0.08  per  cent  its  effects  [on  red-shortness]  are 
probably  almost  completely  effaced  by  the  presence  of  0.80  per  cent  man- 
ganese, since  with  this  composition  the  red-shortness  is  so  slight  that  T  rails, 
the  formation  of  whose  thin  flanges  necessitates  great  malleablness,  can  be 
rolled  with  so  little  cracking  that  at  some  mills  only  0.4  per  cent  of  the  rails 
made  are  of  second  quality  (i.e.,  have- cracked  flanges). 

"  Pieces  of  a  shape  which  can  be  produced  without  necessitating  such 
extreme  malleableness  as  the  formation  of  the  thin  flanges  of  T  rails  requires 
may  contain  more  sulphur;  but  it  is  rare  to  find  more  than  0.12  sulphur  in 
any  steel.  Crucible  tool-steel  has  ordinarily  less  than  0.01  per  cent.  Kail- 
plate  has  usually  from  0.05  to  0.10,  boiler-plate  from  0.02  to  0.08,  per  cent. 

"  Manganese  counteracts  the  effects  of  sulphur.  In  many  cases  4.5 
parts  by  weight  of  manganese  so  far  counteract  the  effects  of  one  part  of 
sulphur  as  to  permit  the  rollfir6  of  flange  T  rails.-"  *  See  also  Appendix  B. 

124.  Tensile  Strength  and  Ductility. — The  effect  of  sulphur  on  the 
tensile  strength  and  ductility  of  iron  and  steel  has  formerly  been  somewhat 
in  doubt.  It  was  known,  of  course,  that  by  producing  red-shortness  it  may 
indirectly  cause  weakness  of  the  cold  specimen  from  external  or  internal 
cracks  resulting  from  the  Hd-shortness  in  the  process  of  rolling.  It  has 
now  been  shown  by  Messrs,  'A'hdrews  and  Arnold,  that  as  small  an  -amount 
of  sulphur  as  0.05  per  cent,  in  the  form  of  sulphide  of  iron,  may  form  in 
thin  meshes,  and  so  very  greatly  reduce  the  strength  and  toughness  of  steel. 
Manganese  reduces  but  silicon  magnifies  this  action.  Annealing  causes 
these  sulphide  flakes  to  collect  in  masses,  thus  largely  destroying  its  weaken- 
ing effects,  f  This  new  and  important  discovery  will  serve  to  explain  some 
of  the  many  astonishing  failures  of  steel  which  have  hitherto  been,  entirely 
unintelligible.  (See  Appendix  B.) 


*  Howe,  pp.  52  and  53. 

t  Prof.  J.  O.  Arnold  in  Trans.  Inst.  Civ.  Engrs.,  vol.  cxxm,  1896,  p.  209  ;  and  Mr. 
Thos.  Andrews  in  Engineering,  Jan.  17,  1896. 


STEEL.  165 


INFLUENCE   OF   PHOSPHORUS    ON   IEON    AND    STEEL. 

125.  In  General. — "  Phosphorus,   the  steel-maker's  bane,  unites  with 
iron  probably  in  all  proportions  at  least  up  to  2G  per  cent,  being  readily 
absorbed  by  it,  especially  at  high  temperatures  and  when  under  deoxidizing 
conditions,  from  acid  phosphates  and  silico-phosphates.     Fortunately  it  is 
readily  removed  from  iron,  especially  under  strongly  oxidizing  conditions, 
by  contact  with  strong  bases  (oxides  of  iron  and  manganese,  the  alkalies  and 
alkaline  earths)  and  by  basic  silicates  and  even  silico-phosphates,  by  alkaline 
carbonates  and  nitrates,  and  by  fluor-spar.     It  is  volatilized  under  many  con- 
ditions,  e.g.,   when  phosphates  are  heated  with  carbon   (the  presence  of 
metallic  iron  more  or  less  completely  prevents  this  volatilization),  and  when 
molten  phosphoric  cast  iron  is  brought  in  contact  with  alkaline  matter  or 
(probably)  with  fluor-spar.      In  the  blast-furnace,  however,  phosphorus  is 
not  effectively  volatilized,  for  any  which  volatilizes  immediately  recondenses. 
Hence  in  the  blast-furnace  nearly  all  the  phosphorus  passes  into  the  metal,, 
though  a  little  is  found  in  the  slag  if  the  deoxidizing  conditions  be  weak. 
In  puddling  90  per  cent,  and  in  the  basic  Bessemer  process  96  to  99  per 
cent,   or  even  more,   of  the  phosphorus  initially  present  may  be  removed 
under  favorable  conditions. 

Phosphorus  increases  the  static  strength  of  low-carbon  iron  and  steel,  but 
it  greatly  reduces  its  resistance  to  shock.  It  increases  the  elastic  limit,  but 
reduces  the  ultimate  elongation  and  contraction.  Carbon  greatly  intensifies 
the  bad  effects  of  phosphorus,  and  silicon  may  intensify  them,  but  certainly 
to  a  very  much  smaller  degree  if  at  all.  "  Rapid  cooling  and  forging  during 
cooling,  by  preventing  the  coarse  crystallization  to  which  phosphoric  iron 
strongly  inclines,  oppose  the  effects  of  phosph  .  on  ductility.  It  is  certain 
that  phosphorus  does  not  always  diminish  the  hot-malleableness  of  iron,  at 
least  at  moderate  temperatures;  buf  by  increasing  the  tendenc}  to  coarse 
crystallization  it  probably  diminishes  malleableness  •  at  very  hfgh  tempera- 
tures, and  especially  when  the  iron  has  slow!/  cooled  without  forging  from  a 
very  high  temperature  to  a  somewhat  lower  V  gh  still  high  one,  as  this 
seems  to  be  the  condition  most  favorable  to  cc  ?  crystallization."  * 

126.  The  Condition  of  Phosphorus  in  Iron.  — "  In  ingot  metal  phosphorus 
exists  chiefly  if  not  exclusively  as  phosphide,  but  in  weld  metal  it  probably 
exists  both  as  phosphide  and  as  phosphate,  i.e.,  as  part  of  the  mechanically 
intermixed  slag,  in  which  condition  it  is  reasonable  to  suppose  that  its  effect 
on  the  mechanical  properties  of  the  metal  should  be  comparatively  slight. 
Many  and  perhaps  an  indefinite  number  Of  phosphides  of  indeterminate  com- 
position may  exist  in  iron,  for  we  find  wide  differences  between  the  chemical 
behavior  of  different  portions  of  phosphorus,  even  in  one  and  the  same  piece 
of  iron,  and  apparently  equally  wide  discrepancies  between  the  effect  of  a 
given  quantity  of  phosphorus  on  the  physical  properties  of  different  irons. 

*  Howe,  p.  54. 


166 


THE  MATERIALS  OF  CONSTRUCTION. 


The  differences  in  the  chemical  behavior  of  phosphorus  are  exemplified  by 
the  fact  that,  on  dissolving  some  steels  in  chlorhydric  acid,  part  of  the  phos- 
phorus escapes  as  phosphoretted  hydrogen,  part  is  found  as  phosphoric  acid, 
part  apparently  as  some  lower  oxygen  acid,  while  still  another  part  is 
insoluble. 

"  The  existence  in  solid  iron  of  a  definite  phosphide  of  iron,  Fe3P,  and 
probably  that  of  a  definite  phosphide  of  manganese,  Mn2P3 ,  is  well  estab- 
lished." * 

1J7.  Effect  of  Phosphorus  on  the  Ductility  of  Soft  Steel. — While  phos- 
phorus seems  to  increase  the  strength  of  low-carbon  steel,  it  very  much 
diminishes  its  ductility,  and  this  is  now  regarded  by  engineers  as  a  very 


jfffi 


•30 


.20 


s 


47/0M  //V 


FIG.  75.— Effect  of  Phosphorus  on  the  Ductility  of  0.10$  to  0.20$  Carbon  Steel.     Num- 
bers indicate  No.  of  Observations  averaged.     (Howe's  Steel,  p.  68.) 

dangerous  ingredient,  and  its  maximum  percentage  is  carefully  specified  im 
the  better  grades  of  structural  steel.     Fig.  75  illustrates  this  effect  on  steel'l 
having  from  one  tenth  to  one  fifth  of  one  per  cent  carbon  (0.10  to  0.20)  andi 
a  tensile  strength  of  from  55,000  to  64,000  Ibs.  per  square  inch,  when  thai 
phosphorus  ingredient  is  less  than  one  tenth  of  one  per  cent.     The  locust 
drawn  on  this  diagram  is  the  most  probable  curve,  showing  the  law  of 
decrease   in   ductility  for   increase  in  phosphorus  for  the   144  tests   here- 
plotted.     Each  plotted  point  represents  the  average  of  the  number  of  tests* 
indicated   in   the   attached   numerals.     When   the   phosphorus   ingredient 
reaches  one  fourth  of  one  per  cent  the  tensile  strength  of  the  same  steel  i&- 
upwards  of  70,000  Ibs.  per  square  inch.     The  diagram  in  this  figure  shows 
a  loss  of  ductility  represented  by  a  diminished  elongation  in  a  length  of  eight 
inches  from  30  per  cent  down  to  10  per  cent,  as  the  phosphorus  ingredient 
rose  from  two  one-hundredths  to  thirty-five  one-hundred  ths  of  one  per  cent, 

*  Howe,  p.  55. 


STEEL. 


167 


While  this  diminution  of  the  percentage  of  elongation  for  increasing  per- 
centages of  phosphorus  is  a  strong  proof  of  increased  brittleness,  various 
impact  tests  on  high-phosphorus  steel,  and  surprising  and  remarkable  acci- 
dents with  such  steel,  lead  to  the  conclusion  that  the  brittleness  of  high- 
phosphorus  steel  under  suddenly  applied  loads  and  under  shock  is  even 
greater  than  would  be  indicated  by  the  diagram  in  Fig.  75.  The  maximum 
proportion  of  phosphorus  now  (189G)  allowed  under  the  better  specifications 
for  structural  steel  is  from  four  one-hundredths  to  eight  one-liundredths  of 
one  per  cent.  This  requirement  is  readily  complied  with  by  the  basic  open- 
hearth  process. 

128.  Effect  of  Phosphorus  on  Static  Strength. — From  over  400  determi- 
nations of  strength  with  corresponding  chemical  analyses,  Mr.  William  II. 
Webster  has  shown  *  that  phosphorus  adds  to  the  static  strength  of  low- 
carbon  steel  approximately  as  indicated  in  the  following  table : 

TABLE    XVI. — EFFECT    OF    PHOSPHORUS    ON"    STATIC    STRENGTH. 


For  Carbon, 

Increase  of  Ultimate  Strength  per 

Effect  of  Unit  of  P  to  Unit 

Hundredths  Per  Cent. 

0.01  Per  Cent  P  added. 

of  C  as  1  to— 

9 

900 

H 

10 

1000 

il 

11 

1100 

if 

12 

1200 

H 

13 

1300 

if 

14 

1400 

if 

15 

1500 

if 

16 

1500 

1* 

17 

1500 

H 

.10  of  one  per  cent. 

.05  J 

.02 


129.  Limiting  Values  of  Chemical  Constituents  Allowable. — Since  nearly 
all  the  constituents  of  iron  and  steel  are  more  or  less  injurious,  it  is  well  to 
specify  the  upper  limits  which  will  be  allowed  in  a  given  product.  These 
upper  limits  should  also  be  placed  as  low  as  possible  without  increasing 
appreciably  the  cost.  Me  teal  f  f  gives,  in  his  work  on  Steel  (1896),  the 
following  as  such  a  set  of  limits: 

"Silicon 

Phosphorus 

Sulphur 

Manganese 

Copper <  .03 

Carbon  to  meet  the  physical  requirements." 

*  See  Trans.  Am.  Inst,  Mining  Engineers,  vol.  xxm.  p.  114. 

f  Wm.  Metcalf,  past  President  Am.  Soc.  Civ.  Engrs.,  who  has  spent  his  life  in 
manufacturing  steel,  and  hence  whose  judgment  in  such  matters  can  be  relied  on. 

\  The  specifications  put  out  in  1896  by  the  Association  of  American  Steel  Manufac- 
turers contain  limitations  of  the  phosphorus  ingredient  of  0.04  for  rivet  and  fire-box 
steel  ;  0.06  for  flange  or  boiler  steel  ;  of  0,08  for  raDway-qridge  steel  ;  and  of  0.10  for 
steel  for  buildings  and  highway  bridges.  (See  Appendix  D.) 


<  .50,  or  even  <  .30 


168 


THE  MATERIALS  OF  CONSTRUCTION. 


The  following  chemical  requirements  were  adopted  by  the  Illinois  Steel 
Co.  for  steel  plates  in  1895: 


Quality. 

Carbon. 

Manganese. 

Sulphur. 

Phosphorus. 

Fire-box.  ...          .  . 

.16 

35  to    50 

Not  over    040 

Not  over    020 

Boiler  

18 

.35  to    60 

045 

"       "       040 

Flanjre               • 

18 

35  to    60 

"       "       045 

"       "       040 

Shin 

15 

35  to    65 

"       '  '       060 

"       «       o^o 

Tank  

*      .10 

.40 

"       ICO 

"       "       120 

HARDENING,    TEMPERING,    AND   ANNEALING. 

130.  Heat  Changes  in  Carbon  Steel. — When  steel  contains  from  0.50  to 
1.00  per  cent  carbon  it  crystallizes  in  a  number  of  ways,  and  the  ingredients 
arrange  themselves  in  a  number  of  different  chemical  combinations  at  differ- 
ent temperatures.  The  changes  in  the  structures  of  steel  when  passing 
through  the  critical  temperatures  are  discussed  in  Art.  107.  Thus  there  is  a 
critical  temperature  between  a  cherry-red  and  a  low-yellow  heat  (about  700°  C. 
or  1300°  F.),  at  which  the  state  of  the  carbon  changes  from  cement  to  com- 
bined (or  hardening)  carbon  as  the  temperature  slowly  rises  past  this  point, 
and  from  hardening  to  cement  again  as  the  temperature  slowly  falls  below  it. 
Thus  at  temperatures  above  700°  C.  the  carbon  is  all  in  the  hardening  state, 
and  the  crystallization  is  that  which  corresponds  to  this  chemical  combina- 
tion. When  the  temperature  slowly  falls  below  this  limit,  however,  the 
carbon  is  expelled  from  its  former  associations,  the  metal  arranges  itself  in  a 
new  series  of  crystals,  and  this  state  of  transition  is  marked  by  many  peculiar 
phenomena. 

(a)  At  this  time,  whether  the  passage  through  this  transforming  region 
be  upward  or  downward,  the  metal  shows  great  weakness.     The  molecules 
seem  to  largely  loose  their  coherence,  and  the  bar  bends  readily,  or  the  metal 
flows  freely  under  a  comparatively  low  stress.     After  passing  this  stage,  in 
either  direction,  the  strength  is  greatly  increased. 

(b)  When  this  stage  is  reached  with  a  rising  temperature,  or  when  the 
cempit  carbon  is  changing  to  the  combined  or  hardening  state,  a  great  deal 
of  heat  is  consumed  to  effect  this  change,  so  that  notwithstanding  the  con- 
tinued absorption  of  heat  the  temperature  ceases  to  rise  for  a  time.     That  is 
to  say,  the  heat  added  here  becomes  latent,  or  does  work  in  effecting  the 
change  in  the  carbon  condition  and  the  new  arrangement  of  the  crystals. 

(v)  When  this  stage  is  reached  with  a  falling  temperature,  the  carbon 
separates  itself  from  its  former  chemical  union  with  the  iron,  and  forms  a 
new  compound  (Fe3C,  carbide  of  iron),  and  the  carbon  is  now  said  to  be  in 
the  cement  state.  This  involves  a  new  crystalline  arrangement  also,  a  tem- 
porary weakening  of  the  metal,  and  a  giving  out  of  the  latent  heat  as  sensible 
heat.  That  is  to  say,  as  the  bar  cools  down  past  this  point  its  temperature 


STEEL  169 

suddenly  increases,  though  in  a  cooling  atmosphere,  from  the  transformation 
of  the  latent  to  sensible  heat.     This  action  is  called  recalescence. 

(d)  As  a  result  of  this  increase  in  temperature  the  contraction  is  changed 
to  an  expansion,  to  be  followed  by  a  contraction  when  the  temperature  begins 
falling  again. 

131.  Hardening  of  Steel. — In  order  to  obtain  a  hardened   steel  it  is 
necessary  to  retain  the  carbon  in  the  hardening  state  (chemically  combined 
with  the  iron  in  the  ratio  of  about  99  Fe  to  1  C)  when  cold.     Although  the 
carbon  always  is  in  this  state  at  high  temperatures  (above  about  1300°  F.), 
yet  it  will  always  change  from  this  to  the  cement  state  in  falling  through 
this  critical  temperature,  if  any  appreciable  length  of  time  is  given  it  to  effect 
the  corresponding  chemical  and  structural  changes.     It  follows,  therefore, 
that  hardening  consists  in  cooling  steel  rapidly  from  a  temperature  above  a 
low-yellow  heat,  in  order  that  it  shall  not  have  time  to  effect  these  changes. 
Doubtless  a  portion  of  this  change  does  occur,  but  with  very  sudden  cooling 
in  a  liquid  bath  most  of  the  carbon  is  retained  in  the  hardening  form.     The 
degree  of  suddenness  of  cooling  depends  on  the  kind  of  liquid  used;  hence 
the  great  variety  of  cooling  baths  in  use,  such  as  mercury,  salt-water,  fresh- 
water,  oil,  tallow,   tar,   etc.     These  liquids  cool  the  steel  with  a  relative 
rapidity  in  the  order  here  named,  mercury  cooling  it  most  rapidly. 

132.  Tempering  of  Steel.* — Having  cooled  a  piece  of  steel  suddenly,  and 
so  retained  its  carbon  in  the  hardening  state,  it  is  usually  found  to  be  too 
hard  and  brittle  for  the  mechanical  uses  to  which  it  is  to  be  put.     It  must 
now  be  softened,  or  tempered,  by  heating  it  up  to  the  proper  temperature, 
and  cooling  slowly,  which  will  suffice  to  change  a  certain  portion  of  the 
carbon  into  the  cement,  or  carbide,  form.     Evidently  the  higher  this  tem- 
perature the  more  complete  will  be  this  change.     Even  though  in  tempering 
the  heat  should  reach  the  critical  low-yellow  stage,  where  the  carbon  takes 
on  the  hardening  form,  if  it  be  followed  by  slow  cooling,  as  in  the  air,  it  will 
change  back  to  the  cement  state,  and  the  piece  will  be  entirely  softened,  or 
annealed.     When  the  reheating  is  well  below  this  critical  temperature,  and 
followed  by  slow  cooling,  the  piece  will  be  softened  in  proportion  to  the 
temperature  reached  and  to  the  time  during  which  it  was  kept  at  such  tem- 
perature.    Thus   any   particular   degree   of   hardness,    or  temper,   can   be 
obtained  by  intelligent  and  skilful  handling. 

133.  Effects  of  Hardening  and  Tempering. — The  effect  of  hardening, 
that  is,  of  sudden  cooling  of  steel  containing  0.50  per  cent  carbon  or  more,  is 
to  retain  the  carbon  mostly  in  the  hardening  state,  and  to  give  a  degree  of 
hardness  proportioned  to  the  percentage  of  carbon  and  the  suddenness  of  the 
cooling.     Not  only  is  the  product  harder,  but  its  strength  and  its  elastic 

*  The  word  "temper"  is  used  in  two  senses.  The  steel-maker  uses  it  to  indicate 
initial  hardness,  as  produced  by  the  percentage  of  carbon,  as  low,  medium,  or  high  tem- 
per. The  user  of  steel  uses  this  term  to  indicate  final  hardness,  as  determined  by  the 
beat  (color)  to  which  hardened  steel  was  reheated,  as  straw,  brown,  blue,  etc.  (See  table 
in  Art.  107.) 


170  THE  MATERIALS  OF  CONSTRUCTION. 

limits  under  all  kinds  of  stress  is  greatly  increased.  The  ductility,  however,, 
is  reduced  as  the  strength  is  increased.  Thus  steel  containing  0.50  per  cent 
0,  which  cooled  in  the  air  after  rolling  at  a  red  heat,  having  a  normal  tensile 
strength  of  67,000  Ibs.,  an  elastic  limit  of  34,000  Ibs.  per  square  inch,  and 
an  elongation  in  eight  inches  of  25  per  cent,  when  heated  to  a  low-yellow 
heat  and  quenched  in  water  will  have  its  tensile  strength  raised  to  150,000 
Ibs.  per  square  inch,  an  increase  of  73  per  cent;  its  elastic  limit  raised  to 
68,000  Ibs.  per  square  inch,  an  increase  of  100  per  cent;  and  its  elongation 
reduced  to  2.5  per  cent,  a  loss  of  90  per  cent.  Such  a  steel  can  now  be 
tempered  and  brought  to  any  condition  intermediate  between  these  limits. 
When  hardened  in  oil  all  the  above  effects  are  less  marked. 

134.  Annealing  consists  in  heating  to  or  slightly  above  the  critical  point 
described  in  the  preceding  articles,  that  is,  to  a  medium  average  color  (or 
655°  0.  or  1150°  F.),  and  cooling  slowly  and  uniformly.  This  removes  all 
the  hardening  effects  of  a  previous  rapid  cooling,  and  it  also  removes  all  the 
internal  stresses  produced  by  a  previous  unequal  heating  and  cooling,  as 
when  portions  of  the  plate  have  been  heated  for  forging,  and  also  the  effects 
of  such  hot  or  cold  working,  as  rolling  and  hammering  when  hot,  or  punch- 
ing, shearing,  bending,  pulling,  crushing,  hammering,  twisting,  rolling,  etc., 
when  cold.  That  is  to  say,  proper  annealing  restores  the  metal  to  its  normal 
condition.  In  the  case  of  steel,  it  changes  all  the  carbon  to  the  cement  or 
non-hardening  condition,  and  at  the' same  time  relieves  all  internal  stresses. 
To  insure  its  full  effects,  however,  the  cooling  should  be  slow  and  uniform 
through  the  entire  mass  of  the  body.  It  should  not,  however,  be  left  to  cool 
down  with  the  furnace,  as  this  holds  it  too  long  at  the  high  temperature. 
It  should  be  removed  from  the  furnace  as  soon  as  heated  through,  but  may 
then  be  covered  with  quick-lime  or  powdered  charcoal,  to  insure  a  slow  and 
even  cooling.  Merely  heating  to  the  required  temperature  and  cooling  in 
the  open  air,  possibly  in  contact  with  cold  metal  surfaces,  and  exposed  to 
draughts,  does  not  satisfy  the  necessary  conditions  of  proper  annealing,  since 
the  cooling  is  too  rapid  and  is  wanting  in  uniformity.  The  heating  should 
be  in  an  oven  large  enough  to  take  the  entire  body,  and  not  by  a  forge,  or 
by  a  fire  built  over  the  body,  and  the  rate  of  heating  should  not  be  too 
rapid. 

Wire  is  usually  annealed  in  cylindrical  pits  built  of  fire-brick,  and  covered 
over,  the  fire  passing  around  them.  This,  and  all  other  processes  of  anneal- 
ing in  which  the  steel  is  exposed  to  the  air,  causes  an  oxide  scale  to  form  on 
the  exposed  surfaces,  which  scale  has  then  so  strong  an  affinity  for  the 
carbon  of  the- underlying  steel,  that  it  decarbonizes  it  to  a  very  slight  depth 
below  the  scale.  While  this  is  of  no  consequence  in  large  masses,  as  in 
structural  forms  or  in  billets,  it  is  quite  fatal  in  such  cases  as  fine  spring-wire, 
or  wire  to  be  made  into  drills,  punches,  graving-tools,  and  the  like,  as  this 
decarbonized  surface  cannot  be  hardened.  To  prevent  this  action  the 
annealing-pots .  are  commonly  filled  with  charcoal,  which  serves  both  to 
exclude  most  of  the  air  and  to  deoxidize  what  is  left,  but  still  some  oxidation 


STEEL.  171 

of  the  steel  surfaces  occur,  with  a  corresponding  decarburization  be- 
neath it.*  This  process  also  fails  to  give  perfect  results,  and  some  other 
means  mast  be  found. 

The  Jones  method  (patented)  consists  in  putting  material  in  a  closed 
tube  from  which  the  air  is  all  expelled  by  some  other  non-oxidizing  gas,  and 
then  placed  in  the  furnace,  and  turned  occasionally,  the  gas  constantly  flow- 
ing through  the  pipe.  This  seems  to  be  a  perfect  method,  the  surfaces 
remaining  absolutely  bright  and  untarnished. 

Metcalf  uses  a  closed  pipe  also,  with  a  loose  cap,  with  resin  thrown  into 
the  extreme  end,  which,  by  volatilizing  on  first  entering  the  furnace,  drives 
nearly  all  the  air  out  of  the  tube.  While  this  method  leaves  the  surface 
slightly  tarnished  it  prevents  all  decarburization  of  the  steel. 

CORROSION. 

135.  Corrosion  of  Iron  and  Steel. — Iron  is  corroded  by  the  combined 
action  of  oxygen  and  water  or  carbonic  acid  and  water.  Neither  of  these 
elements  acting  alone  will  start  corrosion  on  iron.  Iron  will  remain  bright 
indefinitely  in  dry  air,  or  in  water  free  from  oxygen  and  carbonic  acid. 
Acid  fumes,  sulphuretted  hydrogen,  chlorine,  etc.,  will  start  corrosion  with- 
out the  presence  of  water.  After  a  rust  coating  has  once  formed,  however, 
it  will  progress  in  dry  air.  Corrosion  proceeds  more  rapidly  when  the  sur- 
face is  alternately  wet  and  dry,  or  when  the  moisture  coating  is  very  thin, 
than  when  deeply  immersed. 

While  cast  iron  resists  corrosion  better  than  wrought  iron  and  rolled 
steel,  when  all  these  have  their  natural  surfaces  unbroken,  yet  if  all  be 
dressed,  and  the  bright  surfaces  exposed,  cast  iron  corrodes  more  rapidly 
than  the  rolled  metal.  No  relation  has  been  established  between  the  chemi- 
cal composition  of  iron  and  steel  and  the  "rate  of  corrosion.  Neither  can  it 
be  affirmed  that  wrought  iron  or  steel  corrodes  the  more  readily.  (See 
Howe's  Met.  of  Steel,  §§  160-169.) 

*  Metcalf  says  it  is  very  common  to  maintain  the  heat  too  long  in  using  this  and  other 
methods  of  annealing,  thus  spoiling  vast  quantities  of  good  steel  every  year.  Some  of 
the  carbon  changes  to  the  graphitic  form  when  the  heat  is  too  long  maintained. — Steel, 
p.  88. 


CHAPTER  X. 

THE  MINOR  OR  AUXILIARY  METALS  OF  CONSTRUCTION  AND 

THEIR  ALLOYS. 

THE   MINOR   METALS. 

136.  Copper. — Copper,  being  found  native,  has  been  used  in  the  arts, 
both  alone  and  alloyed  with  tin  and  zinc,  from  the  earliest  times.     It  is  so 
commonly  used  now  for  electric  conductors  that  its  more  important  qualities 
are  well  known.     Its  specific  gravity  is  from  8.6  in  castings  to  8.9  in  rolled 
and  drawn  forms,  giving  thus  an  average  weight  of  550  Ibs.  per  cubic  foot. 
It  melts  at  about  2000°  F.,  volatilizes  at  a  white  heat,  and  when  cold  does 
not  oxidize  in  dry  air,  but  does  in  a  moist  or  acid  atmosphere.     It  unites 
with  oxygen  at  a  red  heat,  forming  both  the  black  and  the  red  oxides,  the 
latter  of  which  is  soluble  in  melted  copper,  and  makes  it  brittle  when  cold. 
Commercial    copper  is  never  pure,*  the  ordinary  ingredients  being  iron, 
arsenic,  antimony,  and  the  red  (cuprous)  oxide.     This  last  can  be  removed 
by  melting  the  copper  with  charcoal  and  stirring  with  a  stick  of  green  wood, 
this  process  being  called  "  poling." 

Cast  copper  has  a  tensile  strength  of  some  25>000  Ibs.  per  square  inch, 
with  a  very  low  elastic  limit,  of  some  8000  Ibs.  When  rolled,  or  drawn  into 
wire,  its  strength  may  be  raised  to  50,000  or  60,000  Ibs.  per  square  inch, 
depending  on  the  amount  of  work  done  upon  it.  It  is  then  "hard-rolled" 
or  "  hard-drawn,"  and  it  has  very  little  ductility.  Its  elastic  limit  is  then 
very  nearly  equal  to  its  ultimate  strength.  By  heating  it  a  bright  cherry- 
red  and  cooling  it  either  slowly  or  quickly,  it  becomes  softened  again,  or 
annealed. 

137.  Zinc,  which  is  commonly  called  "spelter"  when  cast,  is  a  hard, 
brittle,  white  metal,  with  a  highly  crystalline  fracture.     It  becomes  malleable 
and  ductile  at  about  200°  to  300°  F.,  but  is  brittle  again  at  higher  temper- 
tures.     Its  specific  gravity  is  6.9  cast  and  7.1  rolled.     It  melts  at  800°  F., 
and  volatilizes  at  about  1900°  F.     It  rapidly  oxidizes  in  air  at  a  red  heat, 
and  at  a  bright  red  heat,  at  which  copper  melts,  zinc  distils.     It  is  mostly 
used  as  an  alloy  in  brass,  German  silver,  etc.,  and  as  a  coating  to  iron  and 
steel  sheets  and  wire,  which  process  is  called  galvanizing.     It  is  a  common 

*  The  Lake  Superior  coppers  are  among  the  purest  in  the  world. 

172 


N    THE  MINOR  METALS  AND   THEIR   ALLOTS.  173 

electropositive  element  in   electric   batteries.     Its  common  impurities  are 
iron,  lead,  and  arsenic. 

138.  Tin. — Tin  is  a  white,  lustrous,  and  extremely  malleable  metal,  as  is 
evidenced  by  its  form  in  tin-foil.    Its  specific  gravity  is  7.3;  it  melts  at  450° 
F.,  but  does  not  readily  volatilize.     Commercial  tin  contains  various  portions 
of  many  elements  such  as  lead,  iron,  copper,  arsenic,  antimony,  bismuth, 
tungsten,  and  sometimes  manganese  and  zinc.     It  is  used  for  coating  iron 
plates,  and  to  alloy  with  copper  and  zinc:     Its  low  melting-point  causes  it 
to  be  used  for  safety-plugs  in  boilers,  as  its  melting-point  corresponds  to  a 
steam-pressure  of  about  400  Ibs,  per  square  inch  above  atmospheric. 

139.  Aluminum  is  a  white,  soft,  malleable  metal  of  extreme  lightness,  its 
specific  gravity  being  only  2.56  when  cast  and  2.75  when  rolled.     It  melts 
at  about  1150°  F.,  but  does  not  volatilize  at  ordinary  melting  temperatures. 
It  is  especially  free  from  oxidation  and  corrosion  in  air,  as  neither  oxygen, 
carbonic  acid,  carbonic  oxide,  sulphuric  or  nitric  acid,  sea-water,  nor  sulphu- 
retted hydrogen  has  much  effect  on  it.     It  is,  however,  readily  dissolved 
by  hydrochloric  acid  and  by  caustic  alkalies.     Its  strength  pure,  when  cast, 
is  only  about  18,000  Ibs.  per  square  inch,  with  low  elastic  limits  in  tension  and 
compression.     When  rolled  or  drawn  into  wire  its  strength  is  raised  to  from 
25,000  to  50,000  Ibs.  per  square  inch  with  elastic  limits  of  about  one  half 
the  ultimate  strength.     It  is  seldom  used  in  a  pure  state  because  of  its 
softness,  but  makes  with  copper,  iron,  zinc,  and  tin  remarkably  strong  and 
malleable  alloys,  which  will  be  discussed  as  aluminum  alloys. 

Aluminum  may  be  rolled  either  hot  or  cold.  It  is  annealed  by  bringing 
it  to  a  low  red  heat  and  cooling  slowly.  In  casting  aluminum  care  must  be 
taken  to  provide  for  the  great  shrinkage.  It  is  best  to  cast  in  hot  iron 
moulds  and  to  cool  from  the  bottom  artificially,  keeping  melted  metal 
supplied  at  the  gate  to  supply  the  shrinkage.  Casting  under  pressure  also 
gives  good  results. 

It  is  difficult  to  obtain  aluminum  in  a  perfectly  pure*  state,  and  very 
slight  amounts  of  impurities  largely  affect  its  properties.  The  common 
impurities  are  iron  and  silicon.  It  is  now  (189G)  supplied  regularly  by  the 
Pittsburg  Reduction  Company,  under  .a  guarantee  of  98  %  pure  at  50  to  55 
cents  a  pound,  and  will  be  furnished  99$  and  99.6$  pure  at  special  rates. 

THE  ALLOYS. 

140.  Nature  of  Metallic  Alloys. — Any  permanent  mixture  of  two  or  more 
metals  is  termed  an  alloy.*     Neither  the  appearance  nor  the  mechanical 
properties  of  an  alloy  can  be  predicated  upon  those  of  the  constituent  metals, 
and  the  surprising  character  of  the  results  produced  by  various  mixtures  has 
led  to  an  enormous  number  ^of  specially  named  products,  each  possessing 
certain  desirable  qualities,  the  ingredients  usually  being,  for  a  time  at  least, 

*  When  mercury  is  one  of  the  constituent  metals  the  product  is  termed  'an  amalgam. 


174  THE  MATERIALS  OF  CONSTRUCTION. 

trade  secrets.  Between  1875  and  1880  the  U.  S.  Test  Board  made  so 
thorough  an  examination  of  all  possible  mixtures  of  the  more  usual  ingredi- 
ents found  in  alloys  (copper,  zinc,  and  tin),  that  the  proprietary  or  trade 
names  formerly  used  exclusively  for  these  products  are  now  giving  place  to 
stated  percentages  of  the  constituent  metals. 

In  a  general  way,  mixtures  composed  almost  exclusively  of  copper  and 
zinc  are  termed  brass,  while  those  composed  mostly  of  copper  and  tin  are 
called  bronze,  while  compositions  of  all  three  of  these  elements  are  called 
composition  metal,  or  perhaps  also  bronze.  All  these  terms  are  used  loosely, 
however. 

An  alloy,  though  ever  so  uniformly  mixed  when  in  a  melted  state,  is 
usually  a  conglomerate  mixture,  after  cooling,  analogous  with  granite. 
Some  pure  chemical  unions  are  formed,  and  certain  substances  may  crystallize 
out,  leaving  the  more  fusible  solution  or  mechanical  mixture  to  form  the 
matrix  for  the  entire  mass  when  cold.  In  most  cases  there  is  a  decided 
tendency  for  the  metals  to  separate  before  cooling,  especially  when  they  are 
of  different  specific  gravities,  this  separating  action  being  called  liquation. 
To  prevent  this  the  mixture  is  stirred  vigorously  just  before  pouring,  which 
is  done  at  as  low  a  temperature  as  possible.  The  quicker  the  metal  cools  in 
the  mould,  also,  the  better,  so  that  it  is  common  to  cast  alloys  in  iron  moulds 
in  order  to  chill  the  metal,  or  to  cool  it  suddenly.  To  obtain  constant 
mechanical  qualities  in  any  given  alloy  seems  to  be  almost  a  practical 
impossibility.  To  secure  even  approximately  uniform  results  requires  more 
care  and  expert  superintendence  than  the  manipulation  of  any  single  metal. 
The  greater  the  number  of  the  constituent  metals,  also,  the  greater  are  the 
difficulties  encountered.  Manufacturers  should  be  slow,  therefore,  to  con- 
tract for  alloys  having  definite  mechanical  qualities  of  a  high  order,  if  they 
have  not  had  a  considerable  experience  in  meeting  with  similar  demands.* 
Almost  as  much  seems  to  depend  on  the  manipulation  as  on  the  metals  and 
proportions  employed;  but  this  subject  is  too  large  to  be  entered  upon  here.f 

141.  The  Copper,  Zinc,  Tin  Alloys. — In  a  general  way,  some  alloy  of  two 
or  moflre  of  these  metals,  copper  being  always  one,  is  used  for  all  purposes 
where  strength,  hardness,  or  malleability  is  desired  in  a  non-corrosive  metal. 
In  other  words,  zinc  and  tin,  one  or  both,  are  added  to  copper  to  harden  and 
strengthen  it.  Formerly  an  alloy  was  used  also  for  large  cast  guns  (then 
called  gun-metal),  but  these  are  now  made  of  hollow-forged  steel.  As  shown 
by  Fig.  76,  the  valuable  alloys  are  those  in  which  copper  forms  the  control- 
ling element.  This  diagram  is  based  on  that  principle  in  geometry  which 
makes  the  sum  of  the  normals  from  any  point  on  the  interior  of  an  equi- 
lateral triangle  equal  to  the  altitude  of  the  triangle.  If  the  three  altitudes 
be  each  taken  as  a  scale  of  equal  parts  on  which  are  indicated  proportions  (per- 
centages) of  copper,  zinc,  and  tin  respectively,  these  ranging  from  zero  to 


*The  author  has  known  of  many  failures  of  contractors  in  this  field, 
t  See  Mixed  Metals,  by  Prof.  Hiorns,  1890,  Macmillan  &  Co. 


THE  MINOR  METALS  AND   THEIR  ALLOYS. 


175 


100,  then  to  the  same  scale  the  sum  of  the  three  normals  from  any  point  in 
the  triangle  will  be  100,  and  hence  these  three  normals  may  be  nsed  to  indi- 
cate the  percentages  of  the  three  metals  which  unite  to  form  that  alloy  which 
is  represented  by  that  point  in  the  triangle.*  An  alloy  of  any  two  of  these 
finds  its  place  along  one  side  of  the  triangle,  of  which  the  three  apices  make 
the  100-per-cent  ends  of  the  three  metal  scales.  A  little  study  of  Fig.  76 
will  make  this  clear. 

The  contour-lines  on  this  figure  were  drawn  by  the  author  after  plotting 
on  this  triangle  the  tensile  strengths  of  cast  bronze  of  'known  composition 


77/V  Z//VC 

FIG.  76.— Showing  the   Tensile  Strength  of   the   Cast  Copper-Tin-Zinc  Alloys  of  all 

Possible  Mixtures.     (Plotted  by  the  author  from  the  results  of  tensile  tests  reported 

by  the  U.  S.  Test  Board  in  1881.) 

from  all  reliable  sources.  Dr.  Thurston's  chart,  after  which  this  is  modelled, 
was  made  from  torsion  tests  by  using  a  constant  factor  to  reduce  to  equiva- 
lent tensile  strength.  The  author  finds  the  tension  tests  themselves*  do  not 
agree  very  well  with  the  values  given  on  that  chart,  and  hence  he  has  drawn 

*  This  method  of  representing  these  triple  alloys  was  first  used  by  Dr.  R.  H.  Thurston, 
Trans.  Am.  Soc.  C.  E.,  1881. 


176  THE  MATERIALS  OF  CONSTRUCTION. 

a  chart  from  the  tension  tests  themselves.  It  must  be  understood,  however, 
that,  as  stated  in  the  previous  article,  so  much  depends  on  the  purity  of  the 
ingredients,  and  on  the  manipulation  of  the  process  of  melting  and  casting, 
that  this  chart,  or  any  similar  record,  must  be  taken  as  showing  what  may  be 
obtained  rather  than  as  what  will  be  obtained  from  the  use  of  these  particular 
mixtures. 

THE   BRASSES. 

142.  The  Brasses — Copper  and  Zinc. — The  most  valuable  brass  alloys  con- 
tain from  65  to  85  per  cent  of  copper  and  35  to  15  per  cent  of  zinc  (3  to  5 
of  copper  to  1  of  zinc).  These  mixtures  are  all  strong  and  ductile,  not  too 
hard  to  be  readily  worked  in  the  lathe  (a  little  tin,  say  2  per  cent,  helps  it 
for  this  purpose),  are  readily  rolled  into  plates  and  drawn  into  wire,  and 
under  various  names  are  the  brasses  of  commerce.  The  French  standard 
mixture  for  sheet  brass  is  67  Cu  to  33  Zn  (2  Cu  to  1  Zn),  and  care  is  taken 
to  use  only  the  purest  metal  for  this  purpose,  as  a  very  slight  amount  of  iron 
or  silicon  (or  lead  in  case  of  wire-drawing)  greatly  lessens  its  ductility. 
Rolled  or  hammered  brass  is  annealed  by  heating  to  a  cherry-red  and  cooling 
either  slowly  or  rapidly. 

Muntz-metal  and  Sterro-metal  are  used  for  ship-coverings  in  place  of 
copper.  The  former  contains  3.8  per  cent  of  zinc,  the  large  proportion  of 
zinc  producing  a  corroded  surface  which  prevents  the  attachment  of 
barnacles.  The  latter  contains,  in  addition,  1.5  to  2  percent  of  iron,  which 
greatly  strengthens  it.  It  is  also  used  for  hydraulic  cylinders  carrying 
very  great  pressures. 

Brass  Castings  should  contain  some  tin  when  used  for  bearings,  as  this 
increases  the  hardness.  Two  or  three  per  cent  is  sufficient.  One  or  two 
per  cent  of  lead  increases  its  adaptation  to  turning,  filing,  and  polishing, 
while  from  i  to  6  per  cent  aluminum  adds  greatly  to  its  strength  and  duc- 
tility. 

In  all  cases,  when  melting  copper,  brass,  or  bronze,  great  care  must  be 
exercised  to  keep  the  air  from  the  metal,  in  order  to  prevent  oxidation. 
This  is  done  by  covering  the  metal,  in  the  crucible,  with  a  thick  layer  of 
powdered  charcoal.  The  copper  is  first  melted  alone,  in  a  deoxidized  flame, 
and  then  the  scrap  brass  and  zinc  (previously  melted,  these  fusing  at  a  much 
lower  temperature)  are  added  and  the  whole  stirred  vigorously  to  effect  a 
thorough  mixing.  Sometimes  this  mixing  is  done  after  the  crucible  is 
removed  from  the  furnace.  If  it  is  done  in  the  furnace,  the  dampers  should 
be  nearly  closed  to  prevent  an  excessive  heat,  which  would  vaporize  the  zinc. 

A  new  brass-melting  furnace  is  shown  in  Fig.  77,*  in  which  crucibles  are 
not  used.  The  metal  is  charged  at  the  upper  door  upon  a  sloping  hearth 
from  which  it  falls,  when  melted,  upon  the  hearth  proper,  from  which  it  is 
drawn  from  the  tap-hole  as  shown.  The  flame  from  the  adjacent  fire  can 

*  Designed  and  built  by  J.  W.  Bennett  &  Co.,  Pittsburg.  From  Engr.  News,  Oct.  1, 
1896. 


THE  MINOR  METALS  AND  THEIR  ALLOTS. 


177 


be  turned  into  either  of  these  chambers  by  the  opening  of  suitable  dampers, 
or  into  both  at  once,  or  stopped  off  entirely  by  the  damper  at  the  top  of  the 
flue.  A  furnace  Jiaving  600  to  800  Ibs.  bosh  capacity  (5000  to  6000  Ibs. 
per  day)  occupies  a  space  of  only  30  to  40  sq.  ft.  By  means  of  the  top 
damper  the  character  of  the  flame  may  be  so  controlled  as  to  prevent  exces- 
sive oxidation. 

If  iron  moulds  are  used,  they  should  be  heated  and  the  interior  surfaces 


FIG.  77. — A  New  Brass- melting  Furnace. 

coated  with  a  mixture  of  resin  (3  pts.)  and  lard-oil  (1  pt.)  to  prevent  adhe- 
sion. In  pouring,  the  metal  must  be  very  carefully  skimmed.  The  pattern 
should  be  made  to  allow  a  shrinkage  of  J  in.  per  foot.  For  common  cast- 
ings green  sand  is  used,  but  for  fine  work  the  moulds  are  dried. 

143.  Delta-metal,  which  is  an  improvement  on  sterro-metal,  is  a  pro- 
prietary composition,  or  brass,  placed  on  the  market  since  1883  by  a  Mr. 
Alexander  Dick  (England),  who  used  the  Greek  form  of  the  initial  letter  of 
his  own  name  to  designate  his  product.  His  process  consists  in  incorporating 
a  fixed  amount  of  iron  by  making  first  a  saturated  solution  of  iron  (about  5 
per  cent)  in  molten  zinc.  To  prevent  all  oxidation  a  little  phosphorus  is 
added  to  the  melted  copper.  The  proportions  are  varied  for  different  pur- 
poses, having  from  50  to  65  per  cent  copper,  50  to  30  per  cent  zinc,  0.1  to 
5  per  cent  iron,  and  sometimes  0.1  to  1  per  cent  tin.  This  metal  is  as  strong 
and  ductile  as  mild  steel,  having  a  tensile  strength,  when  rolled  and  annealed, 
of  from  60,000  to  80,000  Ibs.  per  square  inch,  with  elongations  in  eight 
inches  of  from  40  to  14  per  cent,  respectively,  at  these  limits.*  When  cast 

*  Tests  made  at  Lloyd's  Proving-house,  as  given  by  Hiovns. 


178  THE  MATERIALS  OF  CONSTRUCTION. 

in  sand  its  tensile  strength  is  45,000  Ibs.,  with  an  elongation  of  10  per  cent. 
It  also  resists  corrosion  perfectly. 

144.  Tobin  Bronze  is  very  similar  to  sterro-metal  and  delta-metal,  the 
iron  ingredient  being  somewhat  less.     Its  composition  is  approximately  60 
per  cent  copper,  38  per  cent  zinc,  1  to  2  per  cent  tin,  with  small  portions 
(0.1  to  0.3  per  cent)  of  iron  and  lead.     Its  remarkable  properties  are  due  to 
its  rolling  and  annealing.     As  placed  on  the  market,*  its  tensile  strength  is 
from  GO, 000  to  80,000  Ibs.  per  square  inch,  with  an  elastic  limit  of  GO  per 
cent  of  its  ultimate  strength,  and  an  elongation  of  from  25  to  15  per  cent  in 
eight  inches  at  these  limits  respectively.     It  may  be  regarded  as  having  all 
the  mechanical  qualities  of  structural  steel,  with  the  advantage  of  being  non- 
corrosive.     It  can  be  procured  in  sheets  from  ^  inch  to  1-g-  inches  thick, 
and  in  round  rods  from  J  inch  to  5  inches  in  diameter.     It  is  readily  forged 
at  a  cherry-red  heat  either  by  hand  or  by  machinery.     It  also  works  well  in 
the  lathe.     It  seems,  therefore,  to  be  a  practically  perfect  non-corrosive, 
engineering  metal. 

THE   BRONZES. 

145.  The  Bronzes — Copper  and  Tin. — Since  tin  is  added  to  copper  solely 
to  harden  it  (it  strengthens  it  very  little),  the  copper-tin  bronzes  may  be  re- 
garded as  a  kind  of  hardened  copper.     The  ancients  used  this  combination 
for  their  cutting-tools,  and  it  is  used  largely  at  the  present  time  to  produce 
a  very  hard,  non-corrosive  metal,  useful  for  many  engineering  purposes. 
If  more  than  25  per  cent  tin  is  used,  the  alloy,  though  hard,  becomes  very 
weak  and  brittle.     The  most  common  mixture  is  that  of  gun-metal,  which 
consists  of  90  per  cent  copper  and  10  per  cent  tin.     If  more  than  5  per  cent 
tin  is  used,  the  metal  loses  most  of  its  malleability  when  cold.     With  about 
20  per  cent  tin  the  metal  is  very  hard  and  sonorous,  making  it  suitable  for 
bells,  gongs,  and  wind-instruments.     The  copper- tin  alloys  are  annealed  by 
sudden  cooling,  as  by  quenching  in  water  from  a  red  heat,  while  by  slow 
cooling  they  are  hardened.     They  differ  in  this  respect  from  nearly  all  other 
metals. 

By  using  33  per  cent  tin  (2  copper  to  1  tin),  a  beautiful,  hard,  perfectly 
white  alloy  is  produced,  called  speculum-metal,  suitable  for  polishing  for 
mirrors,  f 

146.  Phosphor-bronze  is  a  plain  copper-tin  alloy  made  by  using  a  little 
phosphorus  as  a  deoxidizer.     It  is  also  claimed  that  the  phosphorus  causes 
the  tin  to  form  a  crystallized  compound  with  the  copper.     It  is  mainly,  how- 
ever, as  a  cleanser  of  the  melted  metal  from  the  oxide  of  copper  that  it  is 
valuable.     When  used  properly  it  forms  a  slag,  and  is  skimmed  off,  and  is 
not  found  in  the  finished  product.     The  phosphorus  is  added  in  the  form 
of  phosphor-copper  or  phosphor-tin,  these  containing  phosphides  of  copper 

*  By  the  Ansonia  Brass  and  Copper  Co.,  New  York. 

f  Lord  Ross's  great  telescopic  reflector  was  made  of  this  alloy. 


THE  MINOR  METALS  AND   THEIR  ALLOTS.  179 

or  of  tin.  For  a  malleable  product,  to  be  rolled  or  drawn  into  wire,  the  tin 
should  not  exceed  4  or  5  per  cent,  and  the  phosphorus  should  not  exceed 
•yL  of  one  per  cent.  For  hard  castings  of  great  strength,  as  for  pinions, 
valves,  bearings,  or  bushings,  use  7  to  0  per  cent  of  tin  and  \  to  1  per  cent 
of  phosphorus.  A  greater  amount  of  phosphorus,  up  to  4  per  cent,  increases 
the  hardness  and  brittleness.  More  than  4  per  cent  phosphorus  will  make 
the  product  useless. 

147.  Silicon-bronze  is  now  used  extensively  in  Europe  for  electric  con- 
ductors, as  it  has  70  per  cent  of  the  conductivity  of  copper,  while  phosphor- 
bronze  has  but  30  per  cent,  and  steel  10,5  per  cent.     By  using  silico-bronze 
wires  the  poles  may  be  put  much  farther  apart  than  when  copper  wires  are 
used.*    While  the  proportion  of  silicon  remaining  in  the  alloy  is  very  small, 
it  has  an  excellent  cleansing  action,  like  phosphorus,  without  danger  of  devel- 
oping brittleness.     The  "dose"  of  silicon,  to  be  added  to  the  melted  copper 
or  bronze,  is  prepared  by  the  inventor,  Weiller,  as  follows:  "  Take  potassium 
silico-fluoride  450  parts  by  weight,  powdered  glass  GOO  parts,  common  salt 
250  parts,  carbonate  of  soda  75  parts,  carbonate  of  lime  GO  parts,  and  dried 
chloride  of  calcium  500  parts.     Heat  these  in  a  covered  plumbago  crucible 
a  little  below  the  temperature  where  they  begin  to  act  on  each  other,  when 
the  whole  is  added  to  the  melted  copper  or  bronze,  and  vigorously  stirred." 
The  resulting  slag  is  skimmed  off. 

148.  Aluminum  Bronze  has  now  come  to  be  regarded  as  one  of  the  most 
valuable  made.     It  is  composed  of  from  5  to  12  per  cent  aluminum  with 
from  95  to  88  per  cent  of  copper.     These  alloys  have  remarkable  ductility, 
combined  with  great  strength.     Thus  the  5  to  7|  per  cent  aluminum  bronzes 
have,  when  rolled  or  forged,  an  ultimate  tensile  strength  of  from  70,000  to 
80,000  Ibs.  per  square  inch,  an  elastic  limit  of  over  40,000  Ibs.,  and  an  elong- 
ation in  8  inches  of  over  30  per  cent.     With  10  per  cent  of  aluminum,  the 
rolled  bars  have  an  ultimate  tensile  strength  of  100,000  Ibs.  per  square  inch, 
an  elastic  limit  of  60,000  Ibs.,  and  an  elongation  of  10  per  bent  in  8  inches. 
If  further  rolled,  it  hardens  and  strengthens  to  130,000  Ibs.  tensile  strength 
with  5  per  cent  elongation.    The  5  to  7  per  cent  bronzes  can  be  hammered, 
rolled,  and  forged  at  a  red  heat,  and  are  very  similar  in  every  way  to  mild  steel. 
They  are  almost  absolutely  non-corrosive.     It  hardens  by  cold  working,  but 
may  be  annealed  by  heating  to  a  red  heat  and  quenching  in  water.     It  has 
a  modulus  of  elasticity  of  about  18,000,000,  which  is  higher  than  that  of  the 
alloys  of  copper,  zinc,  and  tin. 

On  account  of  the  excessive  shrinkage  of  this  alloy  in  hardening,  it  is 
necessary  to  provide  a  large  sinking  head  in  casting,  and  to  so  locate  this  as 
to  supply  to  the  cast  form  the  necessary  fluid  metal  to  give  a  sound  casting 
as  it  shrinks  away  in  cooling. 

*  The  Austrian  Railway  Company  puts  its  poles  from  328  to  720  feet  apart  in  open 
country  when  using  silico-brouze  wires. 


180 


THE  MATERIALS  OF  CONSTRUCTION. 


149.  Alloyed  (or  Hardened)  Aluminum. — Just  as  a  small  percentage  of 
aluminum  added  to  copper  greatly  hardens  and  strengthens  it,  without  de- 
stroying its  ductility,  so  a  small  percentage  of  copper  added  to  aluminum 
works  a  similar  change  in  this  soft  metal.     If  more  than  15  or  20  per  cent 
o'f  either  be  added  to  85  to  80  per  cent  of  the  other,  however,  the  resulting 
mixtures  become  hard,  weak,  and  brittle,  and  entirely  worthless  as  commer- 
cial products. 

Both  tin  and  zinc,  up  to  15  per  cent,  are  used  to  harden  and  strengthen 
aluminum,  while  an  alloy  of  15  per  cent  zinc,  3  per  cent  tin,  and  S2  per 
cent  aluminum  is  especially  recommended.  There  are  a  number  of  secret 
mixtures  of  hardened  aluminum,  some  of  which  are  used  for  casting  bicycle- 
frames. 

150.  Aluminum  in  Steel. — If  about  one  pound  of  aluminum  per  ton  of 
steel  be  added  to  the  heat  just  before  drawing  or  teeming,  it  prevents  the 
formation  and  escape  of  gases,  and  gives  solid  ingots  or  castings.     For  steel 
castings  two  to  three  pounds  per  ton  is  now  commonly  added  to  the  melted 
steel  by  throwing  small  pieces  into  the  ladle  as  the  steel  is  drawn  from  the 
furnace.     In  both  methods  it  permeates  the  entire  mass  without  artificial 
stirring,  as  manganese  does,  and  seems  to  have  very  much  the  same  effect. 
Its  effect  on  cast  iron  are  the  same  as  those  of  silicon,  but  as  it  is  much  more 
expensive  it  is  not  used  in  this  way.     In  steel,  however,  its  use  is  common, 
as  nothing  seems  to  take  its  place.     Besides  preventing  blow-holes  it  adds 
to  the  ductility  of  the  product. 

151.  Alloys  which  Fuse  below  the  Boiling-point. — The  following  remark- 
able alloys,  all  of  which  fuse  at  very  low  temperatures,  may  be  used  as  safety- 
plugs  in  automatic  fire-spraying  pipe-systems  in  mills  and  for  similar  pur- 
poses. 

TABLE   XVII. — FUSIBLE   ALLOYS. 


Name. 

Percentage  of  Ingredients. 

Fusing 
Tempera- 
ture. 

Bismuth. 

Lead. 

Tin. 

'Cadmium. 

Newton's          .                            .... 

50 
50 
50 
50 
50 

31 

28 
25 

24 

27 

19 
22 
25 
14 
13 

0 
0 
0 
12 
10 

95°  C. 
100°  C. 
93°  C. 
66-71  °C. 
60°  C. 

Rose's  

Darcet's  

Wood's 

L/ipoirtz's  .    .    . 

CHAPTER  "XL' 
LIME,  CEMENT,  MORTAR,  AND  CONCRETE. 

LIME  AND  NATURAL  CEMENT. 

152.  Quick,  or  Fat,  Lime.— If  carbonate  of  lime  (CaC03),  as  found  in 
ordinary  limestone,  or  marble,  or  chalk,  be   heated  to  a   temperature   of 
about  800°  F.,  when  it  becomes  a  cherry-rod,  the  carbon  dioxide  (C0a)  is 
driven  off,  and  the  oxide  of  calcium  (CaO)  remains,  and  is  called  quick- 
lime.    In  a  pure  carbonate  of  lime  4-1  parts  by  weight  of  carbon  dioxide 
(carbonic  acid)  are  combined  with  56  parts  by  weight  of  oxide  of  calcium, 
or  quicklime.     Since  the  rock  will  contain  some  moisture,  the  amount  of 
quicklime  obtained  from  burning  limestone  will  never  be  more  than  one 
half  the  weight  of  the  stone  charged.     The  calcium  oxide,  or  quicklime, 
cannot  be  decomposed  by  heat,  but  it  has  a  very  strong  affinity  for  water. 
When  water  is  added  to  it,  it  rapidly  rises  in  temperature,  swells,  and  falls 
into  an  impalpable  powder,  and  increases  its  volume  to  about   three  times 
its  initial  volume  before  the  water  was  added.     This  process  is  called  slack- 
ing, and  the  product  is  then  called  hydrated,  or  fat,  lime  (calcic  hydrate),  or 
slacked  lime,  or  lime  paste  or  putty  when  further  diluted  with  water.     The 
quicklime,  or  calcium  oxide,  will    slack  by  absorbing  moisture   from   the 
atmosphere,  unless  kept  in  closed  vessels.     It  is  therefore  not  kept  in  stock 
for  any  great  length  of  time,  as  it  becomes  bulky  and  difficult  to  handle 
when  slacked.     It  can  be  kept  indefinite^  without  deterioration  in  the 
form  of  lime  paste,  or  putty,  if  kept  wet  so  as  to  exclude  the  air.     Quick- 
lime is  not  found,  as  such,  in  nature,  since  it  has  a  tendency  to  recombine 
with   carbonic   acid  from  the  atmosphere,    and  form    carbonate   of    lime. 
Rocks  composed  of  nearly  pure  carbonate  of  lime  are  found  in  all  parts  of 
the  world,  and    they  have   been  used    in  this  way  for  the   manufacture  of 
-quicklime  for  mortar  from   the  most  ancient  times.     In  slacking,  18  parts 
by  weight  of  water  unite  with  56  parts  by  weight  of  quicklime,  making  74 
parts  of  calcic  hydrate,  Ca(OH)2.     The  heat  generated  in  slacking  greatly 
facilitates  the  process,  and   some  limes  will   slack  in  boiling  water  whicn 
cannot  be  slacked  by  the  use  of  cold  water.     Limes  of  this  latter  class  are 
called  "  poor,"  in  distinction  from  those  which  slack  readily,  which  are 
commonly  termed  "fat." 

153.  Hardening   of  Lime-mortar. — When  quicklime  has   been   slacked 
and  mixed  with  sand  it  forms  what  is  commonly  called  lime-mortar,  which 

181 


182  THE  MATERIALS  OF  CONSTRUCTION. 

is  used  for  laying  brick  and  stone  masonry,  for  plastering  houses,  and 
the  like,  where  the  mortar-joints  will  be  exposed  to  the  action  of  the  air 
only.  Because  of  the  great  shrinkage  of  lime-paste  in  drying,  it  cannot  be 
used  neat,  but  must  always  be  mixed  with  several  times  its  volume  of  sand. 
"When  exposed  to  atmospheric  action,  the  hydrated  lime,  Ca(OH)2,  slowly 
unites  with  carbonic  acid  (C02),  which  is  always  present  in  the  atmosphere, 
thus  changing  a  portion  of  the  hydrated  lime  back  to  its  original  form  of 
carbonate  of  lirne,  leaving  another  portion  in  the  hydrated  form.  Since  the 
carbonic  acid  can  have  access  to  the  lime  only  by  the  circulation  of  air 
through  it,  it  follows  that  this  chemical  change  occurs  mostly  at  the  outer 
and  exposed  surfaces  of  lime-mortar  joints,  and  does  not  take  effect  at  a 
distance  from  the  surface  to  any  appreciable  extent,  except  through  the 
lapse  of  long  periods  of  time.  In  all  cases,  therefore,  where  it  is  neces- 
sary for  the  mortar  to  harden  in  a  comparatively  short  time,  lime-mortar 
must  not  be  used. 

154.  Hydraulic  Lime. — When  a  limestone  contains  from  10  to  20  per 
cent  of  clayey  matter,  new  combinations  of  lime  and  the  silica  in  the  clay 
are  formed  in  the  furnace,  if  the  temperature  is  sufficiently  high,  which 
causes  the  product  to  slack  less  readily,  and  with  a  much   less  increase  of 
volume,  than  in  the  case  of  quicklime.     Hydraulic  lime  is  partially  slacked 
on  drawing  from  the  kiln  by  adding  from  15  to  20  per  cent  of  its  weight  of 
water,  and  it  is  then  thrown  into  large  heaps.     The  steam  thus  formed 
causes  it  to  slack  in  the  course  of  a  week,  after  which  it  is  screened  and 
packed  for  market.     It  cannot  be  kept  in  the  form  of  paste,  as  fat  lime 
always  is,  as  it  would  harden,  like  cement.     If  this  same  rock  be  calcined  at 
a  high  heat  and  reduced  to  a  clinker  but  not  fused,  and  then  ground  with- 
out slacking,  it  forms  the  natural  cement  described  in  the  next  article.     It 
is  changed  from  the  one  product  to  the  other  by  the  chemical  reactions 
which  occur  at  the  higher  temperature  in  the  kiln.     Mortar  made  with  this 
lime  will  harden  somewhat  under  water,  by  a  process  of  partial  crystalliza- 
tion, and  hence  it  is  called  hydraulic  lime.     Limestones  having  a  composi- 
tion suitable  to  make  hydraulic  lime  are  very  common  in    England   and 
Europe,  but  are  not  common  in  America;  hence  what  is  there  known  as 
hydraulic  lime  is  not  known  in  America  as  an  article  of  commerce. 

155.  Natural  Cement. — Carbonate  and  magnesian  limestone  rocks  con- 
taining from   20  to  40  per  cent  of  clay,  when  calcined  to  a  clinker,  just 
short  of  fusion,  and  finely  ground,  give  a  product  which  sets  or  hardens 
quickly  on  the  addition  of  about  25  per  cent  of  its  weight  of  water,  without 
any  increase  of  volume,  and  forms  a  permanent  artificial  stone  which  in- 
creases in  strength  and  hardness  for  many  years.     This  product  is  known 
as  natural  cement*  because  it  is  produced  wholly  from  a  natural  rock.     It 

*  In  England  and  on  the  Continent  this  kind  ef  cement  is  commonly  called  Roman 
cement,  from  a  supposed  similarity  to  the  cement  the  Romans  used  on  their  hydraulic 


LIME,  CEMENT,  MORTAR,  AND   CONCRETE.  183 

has  become  customary  to  give  to  natural  cements  local  geographical  names, 
indicating  the  place  of  their  manufacture.  This  is  more  especially  appro- 
priate since  the  natural  cements  made  in  a  given  locality  will  have  the 
same  general  characteristics,  because  they  are  all  made  from  the  same  sedi- 
mentary rock.  These  cements  are  very  largely  used  in  America,  some  of  the 
principal  varieties  being  the  "  Rosendale  "  cement,  made  near  the  Hudson 
River  in  Ulster  County,  N.  Y.,  the  "  Utica  "  cement,  made  at  Utica,  111., 
the  "Louisville"  cement,  made  mostly  on  the  Indiana  side  of  the  Ohio 
River  in  the  vicinity  of  Louisville,  Ky.,  and  the  "  Milwaukee"  cement, 
made  at  Milwaukee,  Wis.  Such  cements  are  made  at  various  other  places 
in  the  United  States  and  Canada,  and  are  known  by  their  corresponding 
local  geographical  names.  These  cements  are  now  very  cheap,  and  often- 
times are  found  to  vary  greatly  in  quality.  While  the  better  grades  of 
natural  cement  are  quite  sufficient  in  strength  for  nearly  all  kinds  of 
engineering  works,  the  want  of  uniformity  in  their  hardening  properties 
is  a  serious  objection  to  their  use. 

Some  of  the  American  natural  cements  are  very  quick  setting,  which  is 
a  further  objection  to  them,  since  it  is  difficult  to  use  the  mortar  or  concrete 
made  from  them  before  it  begins  to  set,  or  harden. 

The  old  Roman  cement  used  by  the  Romans  in  their  hydraulic  masonry 
constructions  was  made  by  mixing  volcanic  ashes  with  lime  in  proper  pro- 
portions. 

PORTLAND  CEMENT. 

156.  Historical. — An  artificial  mixture  of  lime  and  clay  in  proper  propor- 
tions, calcined  to  a  clinker  at  a  temperature  of  incipient  fusion,  and  finely 
ground,  is  called  Portland  cement.  It  received  this  name  in  1824  in  Eng- 
land, where  it  was  first  made,  from  its  similarity  in  appearance  when 
hardened  to  the  noted  oolitic  limestone  from  the  "  Isle  of  Portland  "  *  long 
used  in  England  for  building  purposes.  It  was  patented  in  that  year  by 
Mr.  Joseph  Aspdin,  a  Leeds  brickmaker,  as  an  "artificial  stone."  He 
mixed  pulverized  limestone,  taken  from  the  public  macadamized  roads, 
with  clay,  by  adding  water  enough  to  reduce  it  to  a  liquid  form.  This  was 
then  dried  and  burned  "  in  a  furnace  similar'  to  a  lime-kiln  till  the  car- 
bonic acid  is  entirely  expelled."  The  necessity^!  burning  to  a  clinker 
was  not  given  in  the  specification,  and  was  pro&ably  not  known  at  that 
time,  neither  was  the  proper  proportion  of  clay  mentioned.  His  success  was 
therefore  something  of  an  accident,  as  was  doubtless  the  discovery  of  the 

engineering  works.  There  are  few  suitable  rocks  in  Europe  for  making  this  cement.  It 
is  extremely  irregular  in  composition,  and  not  to  be  compared  with  the  very  uniform 
beds  found  in  inexhaustible  quantities  in  the  United  States.  If  such  natural-cement 
rocks  as  we  have,  had  been  common  in  England  and  on  the  Continent,  it  is  almost  certain 
that  the  artificial  Portland  cement  would  never  have  been  discovered. 

*  This  is  really  a  peninsula  on  the  south  coast  of  England,  in  Dorset,  near  Weymoutb, 
noted  for  its  building-stone.  The  Westminster  cathedral  is  built  of  this  stone. 


184  THE  MATERIALS  OF  CONSTRUCTION. 

hydraulic  property  of  the  mixture  itself.     Aspdin  began  manufacturing  his 
cement  at  Wakefield  *  in  1825. 

Previous  to  his  time  a  kind  of  natural  cement  had  become  common 
under  the  general  name  of  "Roman  cement."  This  was  made  by  calcining 
nodules  (geodes)  of  a  clayey  limestone  found  along  the  seacoast,  "  at  a  heat 
nearly  sufficient  to  vitrify  them,"  and  grinding  the  product.  (Patented  by 
James  Parker  in  England  in  1796.) 

The  discovery  that  the  hydraulic  property  of  certain  limes  was  due  to 
the  clay  ingredient  is  due  to  Smeaton  (about  1756),  who  had  some  knowl- 
edge of  chemistry. f  The  occasion  of  these  investigations  was  the  building 
of  the  first  Eddystone  lighthouse.  This,  therefore,  marks  the  beginning 
of  all  intelligent  study  of  the  subject  of  hydraulic  cements.  J 

Although  Aspdin  began  manufacturing  Portland  cement  in  the  north 
of  England  in  1825  (and  continued  to  1853),  and  it  was  introduced  exten- 
sively on  the  Continent,  it  was  not  known  in  London  till  made  by  J.  M. 
Maude  and  Son  (with  Aspdin's  son)  in  1843  under  Aspdin's  patents  in  what 
is  now  a  part  of  London,  and  by  J.  B.  White  and  Sons,  in  Kent,  in  1845.  § 

In  tests  made  in  1843  for  the  new  Houses  of  Parliament  this  Portland 
-cement  was  shown  to  be  superior  to  the  Eoman  cement  then  in  common 
use,  but  engineers  and  architects  were  slow  to  grant  the  fact.  Public  com- 
petitive tests  between  the  above-named  firms  were  conducted  in  1848 
which  further  proved  the  superiority  of  the  Portland  cement,  |  and  after 
the  Exhibition  in  1851,  at  which  many  tests  were  made,  its  use  soon  became 
general  in  England. 

Many  failures  marked  the  first  thirty  years  of  the  Portland-cement 
manufacture,  from  an  entire  neglect  of  the  chemical  analysis  of  the  ingredi- 
ents. Reliance  was  placed  solely  on  the  empirical  knowledge  of  workmen 
ignorant  of  chemical  science,  and  much  sophistry  and  deception  were  used 
to  cover  up  their  failures.  It  is  now  known  that  good  Portland  cement 


*  A  small  city  in  Yorkshire  near  Leeds. 

f  A  report  of  his  investigations  and  conclusions  was  not  published  till  1791,  in  Book 
IV  of  his  Narrative  of  the  Building,  etc.,  of  the  Eddystone  Lighthouse. 

^  For  a  very  good  account  of  the  early  history  of  >  this  subject  see  Redgrave's  Cal- 
careous Cements,  London,  1895. 

§  This  was  a  Roman  cement  factory,  but  Mr.  I.  C.  Johnson,  their  manager,  after 
long  search  and  experimentation,  the  Aspdin  processes  being  secret  and  purposely  mys- 
tified, discovered  the  secret  of  burning  to  a  clinker.  He  also  at  last  discovered  the 
proper  proportions.  From  an  account  by  Mr.  Johnson  himself  in  The  Building  News 
(London),  1880. 

||  These  tests  consisted  in  building  out  brick  beams  from  solid  walls,  and  in  crushing- 
tests  of  large  cement  prisms.  As  late  as  1845-6  Sir  Robert  Peel  announced  in  Parlia- 
ment his  intention  of  taxing  the  use  of  the  clay  nodules  of  which  the  Roman  cement  was 
then  made,  to  prevent  their  complete  exhaustion,  and  to  retain  sufficient  of  them  for 
government  works.  Aspdin  thereupon  addressed  him  a  personal  note  describing  his 
artificial  cement,  and  the  proposed  measure  was  dropped. 


LIME,  CEMENT,  MORTAR,  AND   CONCRETE.  185 

can  be  made  anywhere  by  properly  combining,  burning,  and  grinding  a 
mixture  of  carbonate  of  lime  and  a  suitable  clay,  the  only  elements  of 
commercial  success  being  economy  and  scientific  direction. 

Since  a  good  Portland  cement,  with  or  without  sand,  gravel,  and  broken 
stone,  makes  an  artificial  compound  equal  to  almost  any  natural  stone  in 
hardness,  strength,  and  durability,  and  since  it  can  be  moulded  to  any  form 
and  is  much  cheaper  than  quarried  and  cut  stone,  it  is  constantly  finding 
wider  and  wider  fields  of  application.  This  material  has  already  worked  a 
revolution  in  engineering  construction  nearly  equal  in  significance  to  that 
following  upon  the  general  use  of  the  Bessemer  and  open-hearth  processes 
of  making  steel.  The  character  of  Portland  cement  also  has  constantly 
improved,  until  now  it  has  reached  practical  perfection.  Within  the  past 
ten  years  the  improvement  has  been  very  marked,  as  a  result  of  the  universal 
system  of  testing  now  in  vogue,  and  of  the  general  employment  of  compe- 
tent scientific  supervision  of  the  works,  made  necessary  by  these  tests  on 
the  part  of  the  user.  Portland  cement  is  now  made  on  a  gigantic  scale  in 
Germany,  Belgium,  France,  and  England,  and  its  manufacture  is  rapidly 
increasing  in  the  United  States. 

157.  The   Ingredients  of  Portland  Cement. — All   mixtures,  natural  or 
artificial,  of  carbonate  of  lime  (CaC03)  and  clay  in  the  proportions  of  from 
72  to  77  per  cent  of  the" former  to  20  to  25  per  cent  of  the  latter  will,  when 
calcined  at   the   proper  temperature,  produce  a  Portland   cement  of  fair 
quality.     After  calcining,  and  driving  the  carbonic  acid   (C02)  from  the 
carbonatelSf  lime  (CaC03),  the  proportions  of  lime  (CaO)  and  clay  (silicate 
of  alumina  (A1308,  2Si02, 2H20)  are  about  60  to  65  per  cent  of  lime  and 
fr0in  25  to  30  per  cent  of  clay,  with  some  5  per  cent  of  other  ingredients, 
such  as  sulphate  of  lime,  magnesia,  iron  oxides,  etc.     "A  variation  in  the 
lime  ingredient  of  one  per  cent  above  the  true  amount  will  give  a  cement 
liable  to  crack  on  long  exposure  to  water,  and  a  deficiency  of  one  per  cent 
of  lime  will  reduce  the  strength  of  the  cement  and  also  make  the  mixture 
liable  to  fuse  in  the  kiln."*     The  most  competent  chemical  supervision  and 
continual  analyses  of  the  ingredients  are  therefore  necessary  to  secure  the 
best  results. 

158.  Chemical   Characteristics    of  the   Ingredients. — The   carbonate   of 
lime  should  be  nearly  free  from  all   other  substances   except  clay  (silica 
and  alumina).     While  magnesia  and  iron  in  small  amounts  are  not  injuri- 
ous, they  are  probably  inert,  and  the  sulphur  compounds  are  a  positive 
injury,  above  a  two  or  three  per  cent  limit. 

159.  The  Clay. — "  The  best  clays  for  the  cement-manufacturer  are"  those 
having  a  greasy,  unctuous,  feeling,  quite  smooth  to  the  touch.     As  a  rule, 
clays  which  stain  the  fingers  should  be  avoided,  as  being  either  too  much 

*  Prof.  Spencer  B.  Newberry  in  the  Engineering  Magazine,  Juue,  1894.  Mr.  New- 
berry  is  chemist  and  manager  of  the  Sandusky,  O.,  Portland  Cement  Works.  This 
Statement  is  probably  a  little  too  strong. 


186  THE  MATERIALS  OF  CONSTRUCTION. 

impregnated  with  iron  compounds,  or  containing  a  large  proportion  of 
organic  or  other  impurities.  This  does  not  hold  good  in  the  case  of  the 
carboniferous  shales,  some  of  which  are  rich  in  matters  which  assist  in  the 
calcination  of  the  cement.  Shales  which  contain  much  alum,  selenite,  or 
iron  pyrites,  and  many  of  the  shales  having  a  high  percentage  of  carbonate 
of  lime,  need  great  care  in  manipulation,  as  they  are  apt  to  fluctuate  widely 
in  composition  and  to  lead  to  mistakes  in  the  proportions  of  the  ingredients. 
Some  clays  contain  a  high  percentage  of  sandy  particles,  or  of  nearly  pure 
silica  not  in  combination  with  lime,  iron,  or  alumina,  and  these  clays,  though 
useful  to  the  brick-maker,  are  ill  adapted  for  cement-making.  They  are 
generally  characterized  by.  a  harsh  gritty  touch  when  tested  between  the 
finger  and  thumb,  and  it  is  possible  to  wash  out  a  considerable  percentage 
of  sandy  particles."* 

160.  Silica  and  its   Compounds. — "  It   will   be   necessary,   in   order   to 
understand  the  chemistry  of  cements,  to  treat  in  some  detail  of  silica  and 
its  compounds.      Silica,  the  oxide  of  the  element  silicon,  is  found  very 
widely  distributed  in  nature,  sometimes  pure,  but  more  often  in  combina- 
tion with  other  substances,  as  it  has  a  great  tendency  to  forrr  complex 
salts,  known  as  silicates.     It  plays  the  part  of  an  acid,  and  combines  with 
lime,  alumina,  iron,  and  the  alkalies  in  a  vast  number  of  different  propor- 
tions.    It  is  found  that  28  parts  by  ^weight  of  silicon  and  32  parts  by  weight 
of  oxygen  are  present  in  silicic  anhydride  or  silica,  having  the  chemical 
formula  Si02.     Clay,  a  hydrous  silicate  of  alumina,  may  oe  taken  as  a  type 
of   the.  silica   compounds,  while  quartz,  flint,  and  chalcedony   consist  of 
almost  pure  silica.     Porcelain  clay,  which  contains  about  47  per  cent  of 
silica,  39.2  per  cent  of  alumina  (A1203),  and  13.7  per  cent  of  water,  and 
corresponds  to  the  chemical  formula  Al2032Si03  +  2II20,  or  clay  proper, 
with  a  molecular  weight  of  258.4,  may  represent  th,e  silicates.     There  are, 
however,  an   enormous  number  of  clays  in  which  silica  and  alumina  are 
present  in  very  varying  proportions,  and  which  contain  in  addition  iron, 
alkaline  matters,  lime,  etc.     For  certain  of  these  clays  it  becomes  almost 
impossible  to  propound  any  reliable   chemical   formula   to   express   their 
composition;  and  alumina,  while  it  may  combine  in  certain  definite  pro- 
portions with  the  silica  as  a  base,  is  also  capable  of  acting  as  an  acid,  and  of 
combining  with  lime  and  the  alkalies,  especially  at  high  temperatures,  to 
form  certain  more  or  less  unstable  and  little  known  compounds  termed 
aluminates."  * 

161.  "  Alumina  is  the  oxide  of  the  metal  aluminum  which  has  the  atomic 
weight  of  27.2,  and  two  parts  of  aluminum  combine  with  three  parts  of  oxy- 
gen, equal  48,  to  form  its  only  known  oxide,  termed  alumina,  amounting  in 
all  to  102.4.     It  will  not  be  necessary  to  study  in  detail  the  combinations  of 
silica  and  alumina  with  iron  and  the  alkalies — soda  and  potash — though 
these  compounds  play  a  very  important  part  in  cement  action."  * 

*  Redgrave. 


LIME,  CEMENT,  MORTAR,  AND   CONCRETE. 


187 


162.  Sulphur  and  its  Compounds. 

Portland  cement  may  be  associated 
with  a  small  percentage  of  gypsum 
or  sulphate  of  lime  (calcic  sulphate 
CaS04,  2H20),  the  water  of  which  is 
driven  off  in  the  calcining  process, 
reducing  this  compound  to  what  is 
commonly  known  as  plaster  of  paris 
(GuS04).  Sulphur  may  also  be  intro- 
duced in  the  fuel  used  for  burning, 
or  from  the  clay  which  sometimes 
contains  iron  pyrites.  The  sulphuric 
acid  relieved  from  these  compounds 
ma  unite  with  the  free  lime  in 


—  The  carbonate  of  lime  used  for  making 


0  5 

F.G.  78.— Effect  of  Plaster  of  Paris  on 
Time  of  Setting  of  Cement.  (Wheeler, 
Rep.  Chf.  Engrs.  1895,  p.  2938.) 


/.a         2.0       3.0 

FIG.  79.— Showing  the  Effect  of  Plaster  of 
Paris  011  the  Strength  of  Portland-cement 
Mortar,  1  C.  :  3  S.  (Tetmajer,  vol.  vn.  p 
39.) 


furnace  and  form  an  additional  portion  of  calcic  sulphate.  The  effect  of 
this  calcic  sulphate  or  plaster  of  paris  in  quantities  not  exceeding  two  or 
three  per  cent  is  to  greatly  delay  the  time  of  setting  (Fig.  78),  but  to 
increase  slightly  the  final  strength  of  the  cement  (Fig.  79).  When  present 
in  quantities  exceeding  four  or  five  per  cent  both  these  effects  are  lost,  and 
it  is  also  considered  injurious  in  other  ways,  since  it  is  comparatively  sol- 
uble in  water,  and  when  present  in  the  kiln  in  considerable  quantity  it 
leads  to  the  formation  of  calcic  sulphide,  which  decomposes  the  iron  com- 
pounds in  the  cement,  thus  leading  to  disintegration.  The  German  standard 
rules  allow  a  proportion  of  calcic  sulphate  not  to  exceed  two  per  cent,  but  an 
effort  has  recently  been  made  to  have  this  limit  raised  to  three  per  cent. 

163.  The  Chemical  Reactions  Produced  in  Calcining. — It  has  been  com- 
monly agreed  by  chemists  that  the  following  combinations  are  effected  by  cal- 
cining an  intimate  mixture  of  lime  and  clay  to  the  point  of  incipient  fusion : 


188 


THE  MATERIALS  OF  CONSTRUCTION. 


Silicate  of  lime  (SiOQ,  3CaO) 


j  Silii 
|Lirr 

Aluminate  of  lime  (AlaOa,  3CaO) j  £! 


Proportions  by 
Weight. 

Silica  23 
Lime  43 
Alumina  17 
jme  28 
Silica  15 

Double  silicate  of  lime  and  alumina  (Si03(Al203-fCaO)3) J  Alumina  51 

Lime        28 

Magnesia  probably  remains  inert,  and  does  not  combine  with  alumina 
and  silica.  It  is  harmless  if  not  forming  over  five  or  six  per  cent  of  the 
whole.*  Oxide  of  iron  is  also  a  useless  ingredient. 

M.  Le  Chatelier  has  been  able  to  identify  the  aluminate  of  lime  by  a 
microscope,  with  polarized  light,  in  both  cement  clinker  and  in  an  artificial 
synthetic  compound.  He  also  thought  he  determined  two  other  substances 
in  this  manner,  they  being  a  silicate  of  lime  (2CaOSi02)  found  crystallized 


4 


out 
COMP/JESS/ON 


/  N 


DAYS 


6000 


0  /40  28O 

FIG.    80. — Showing  the  Inferior   Character  of  the  Furnace-dust   compared   with   the 
Ground  Clinker,  when  used  in  Mortar,  1C.:  3S.    (Tetmajer,  vol.  vn.  p.  12.) 

in  a  matrix  of  an  alumino-ferrite  of  lime,  with  a  formula  2(AlFe)2033CaO. 
These  chemical  reactions  in  the  furnace  are,  however,  not  yet  known  with 
certainty. 

Since  there  is  no  further  mixing  of  the  lime  and  clay  ingredients  in  the 
furnace  in  the  calcining  action,  it  is  absolutely  necessary,  in  order  to  secure 

*  The  German  Cement  Manufacturers' Association  has  allowed  five  per 'cent  since 
1893. 


LIME,  CEMENT,  MORTAR,  AND   CONCRETE.  189 

perfect  results,  to  have  the  lime  and  the  clay  perfectly  and  uniformly 
mixed  before  going  into  the  furnace;  that  is  to  say,  each  particle  of  lime 
should  have  adjacent  to  it  its  particle  of  clay  with  which  to  unite  when  the 
proper  temperature  has  been  attained.  Since  it  is,  of  course,  impossible  to 
intermix  these  materials  to  this  degree  of  perfection,  there  must  of  necessity 
result  from  the  burning  more  or  less  inert  or  un combined  clay  and  lime 
without  cementing  qualities,  which  inert  matter  forms  a  large  part  of  the 
furnace-dust.  (See  Fig.  80.)  If  the  ingredients  were  actually  fused  or  melted 
into  a  liquid  mass,  and  the  chemical  action  were  to  take  place  after  the 
ingredients  were  in  the  liquid  form,  a  much  more  perfect  union  of  the  ele- 
ments would  of  course  be  effected.  In  the  formation  of  the  clinker  which 
is  ground  into  Portland  cement,  however,  the  ingredients  are  not  fused, 
since  fusion  would  be  fatal,  and  hence  the  elements  of  the  mixture  are 
incapable  of  uniting  except  they  be  in  immediate  juxtaposition.  The 
further  improvement  of  Portland  cement  evidently  lies  in  the  direction  of 
more  perfect  and  more  uniform  mixture  of  the  raw  materials  in  a  finely 
divided  state  before  they  are  burned.  From  experimental  tests  which 
have  been  made  in  this  direction,  it  would  seem  that  the  strength  of 
Portland  cement  might  be  made  at  least  twice  what  it  is  now,  by  more 
perfectly  satisfying  this  requirement. 

164.  The  Chemical  and  Physical  Changes  involved  in  Setting  and 
Hardening. — By  the  setting  of  cement  is  meant  its  initial  change  from  a  soft 
or  plastic  mortar  to  a  friable  solid.  This  change  is  usually  effected  with 
great  suddenness,  after  it  begins,  as  shown  by  the  curves  in  Fig.  333,  and 
it  has  been  shown  to  be  always  accompanied  by  the  evolution  of  heat. 
After  the  cement  has  become  thoroughly  set  it  still  is  very  weak,  and  is 
readily  pulverized  in  the  fingers.  If  left  undisturbed,  however,  it  increases 
in  hardness  and  strength,  sometimes  for  several  months,  but  generally  for 
many  years.  There  is  no  relation  between  the  time  elapsing  after  wetting 
before  setting  takes  place,  and  the  period  of  time  required  to  attain  to 
nearly  its  ultimate  strength.  The  setting  of  cement  is  thought  to  be  effected 
by  the  crystallizing  out  of  the  silicate  and  the  aluminate  of  lime,  which 
are  soluble  in  water  in  their  anhydrous  form.  After  dissolving  in  the 
water  they  pass  to  the  hydrated  state  in  which  they  are  insoluble,  and  hence 
are  precipitated  in  a  crystalline  form,  with  a  development  of  heat.  This 
process  is  greatly  hastened  at  higher  temperatures. 

The  hardening  of  cement  is  due  to  a  continued  crystallization  of  salts 
from  solution,  and  to  further  chemical  and  physical  changes  which  develop 
slowly,  but  which  continue  for  long  periods  of  time.  M.  Fremy  regards  the 
aluminate  of  lime  as  the  chief  source  of  the  hardening  property,  and  he  also 
thinks  the  silica  and  the  alumina  of  the  clay  are  separated  by  calcining  and 
take  on  allotropic  forms,  ready  to  unite  into  new  compounds  with  the  quick- 
lime when  water  is  added.  There  are  so  many  kinds  of  combinations  of 
various  substances  which  will  serve  to  produce  the  final  characteristics  of 


190 


THE  MATERIALS  OF  CONSTRUCTION. 


hardened  Portland  cement,  that  there  must  be  many  different  chemical 
compounds  which,  after  calcining,  will  harden  on  the  addition  of  water. 

The   problem   is   so    complicated 

^..   ^  „  ,,  ^  „  „. -•-^Jl--         .^.     .   that  ^  nas  as  T?e^  Defied  a  complete 

chemical  analysis. 

165.  Slag-cements. — Many  va- 
rieties of  iron  blast-furnace  slags 
will  make  an  excellent  cement 
when  ground  with  hydrated  or 
slacked  lime,  without  further  cal- 
cining. The  slag  is  "  granulated  " 
by  running  it  from  the  blast-fur- 
nace into  water,  where  it  forms  into 
a  brittle,  porous,  pumice-like  mass 
resembling  caked  sand,  and  in  this 
condition  it  is  called  "  slag-sand/' 
It  is  now  easily  crushed  into 
powder,  but  retains  the  water  in 
its  meshes  so  that  it  is  very  diffi- 
cult to  dry  it.  Sometimes  this 
"  slag-sand  "  is  calcined  at  a  low 
heat  simply  to  dry  it. 

This  method  of  suddenly  cool- 
ing the  melted  vitreous  slag  in 
water  has  no  effect  upon  it  further 
than  to  simply  reduce  it  to  the 
porous,  friable  condition,  since 
when  allowed  to  cool  in  the  ordi- 
nary way,  into  a  solid  mass,  and 
then  crushed  to  powder  and  lime 
added,  it  has  no  hydraulic  proper- 
ties (see  Fig.  81).  It  seems  prob- 
able, therefore,  that  the  sudden 
cooling  leaves  the  chemical  com- 
pounds in  a  mere  unstable  con- 
dition, so  that  when  powdered 
and  intimately  mixed  with  hy- 
drated lime,  and  water  added, 
they  are  ready  to  enter  into  new 
chemical  combinations  with  the  lime.  To  three  parts  by  weight  of  the 
dry  "slag-sand"  is  added  one  part  of  hydrated  lime  (CaII202),  and  these 
are  thoroughly  ground  together  and  intermixed  by  suitable  mechanical 
appliances.  This  cement  does  not  deteriorate  appreciably  by  lapse  of 
time. 


a- 


\ 


LIME,  CEMENT,  MORTAR,  AND   CONCRETE.  191 

The  burdening  properties  of  slag-cement,  with  its  small  proportion  of 
lime,  and  its  being  an  artificial  mixture  of  free  lime  and  slag  without  subse- 
quent calcining,  have  greatly  disturbed  the  previously  accepted  theories  of 
the  chemical  transformations  in  the  furnace  and  after  melting,  in  the  case 
of  Portland  cements,  and  it  seems  that  now  the  whole  matter  will  have  to 
await  a  further  progress  of  chemical  knowledge  in  this  direction. 

Slag-cements  make  a  more  unctuous  mortar  and  are  much  liked  by 
architects  for  laying  brick  Avails  and  piers,  and  for  making  floors,  sidewalks, 
etc.  It  is  slow  setting  and  does  not  stain  the  masonry  in  outside  walls.  It 
is  often  mixed  with  additional  amounts  of  lime-putty  to  further  delay  the 
time  of  setting,  or  to  cheapen  the  mortar,  or  to  make  it  work  smoother 
under  the  trowel,  or  perhaps  for  all  these  reasons  combined. 

166.  Sources  of  the  Raw  Materials  Used  in  Making  Portland  Cement.*— 
"  Portland  cement  is  made  from  carbonate  of  lime  and  clay.  These  materials 
may  be  naturally  mixed,  as  in  the  case  of  argillaceous  limestones,  or  entirely 
separate.  In  all  cases,  however,  it  is  necessary  to  bring  the  material  to  cor- 
rect composition  by  artificial  additions  and  thorough  mixing.  In  England 
chalk  is  the  form  of  carbonate  of  lime  employed.  In  Germany  the  chief 
material  is  marl  (mergel),  by  which  is  understood  a  more  or  less  hard  lime- 
stone rock  containing  clay.  In  some  German  factories  a  pure  soft  marl 
(weisenkalk),  or  fresh-water  chalk,  is  used,  consisting  chiefly  of  carbonate 
of  lime  and  similar  to  the  marl  deposits  of  this  country. 

"  In  the  United  States  the  materials  used  are  very  similar  to  those  of 
Germany.  Most  of  our  clay  limestones  are  highly  magnesian,  and  there- 
fore unsuitable  for  Portland  cement,  though  they  are  used  on  an  immense 
scale  for  natural-rock  cements.  At  certain  localities,  however,  as  in  Lehigh 
County,  Pa.,  at  Phillipsburg,  N.  J.,  and  in  the  far  West,  limestones  con- 
taining sufficient  clay  and  nearly  free  from  magnesia  are  abundantly  found, 
and  in  the  above  localities  and  from*  this  material  most  of  our  Portland 
cement  is  made.  In  the  Lehigh  County  region,  the  chief  seat  of  the 
American  Portland-cement  industry,  the  different  strata  of  rock  are  care- 
fully selected  and  mixed  in  such  proportions  as  to  give  a  material  of  the 
right  composition. 

"  In  central  New  York  and  at  a  few  points  in  Ohio  and  Indiana  large 
deposits  of  pure  white  marl  are  found.  This  is  generally  called  ' shell- 
marl/  and  was  supposed  to  result  from  the  disintegration  of  fresh-water 
shells.  In  the  opinion  of  the  writer,  however,  these  marl-beds  are  generally 
pulverulent  deposits  from  calcareous  springs,  and  are  not  formed  from 
shells  to  any  great  extent.  At  the  localities  above  mentioned  this  material, 
artificially  mixed  with  clay,  is  largely  used  for  the  manufacture  of  Portland 
cement.  Owing  to  the  soft,  fine-grained  character  of  the  marl,  the  mixing 
can  be  much  more  cheaply  done  than  in  the  case  of  limestone,  though  this 

*  This  and  the  following  article  are  taken  from  the  paper  on  Portland  Cement  by 
Prof.  Spencer  B.  Newberry,  in  the  U.  S.  Geol.  Surv.  Report  for  1894,  Part  IV,  p.  581. 


192 


THE  MATERIALS  OF  CONSTRUCTION. 


advantage  is  largely  compensated  for  by  the  necessity  of  drying  out  the  40 
to  50  per  cent  of  water  which  the  marl  generally  contains.  It  must  be 
remembered  also  that  in  the  argillaceous  limestones  the  ingredients  are 
already  uniformly  mixed  in  nearly  the  proper  proportions,  while  with  the 
pure  lime  and  clay  this  mixing  must  be  wholly  effected  by  artificial  means. 
The  leaving  of  any  free  lime  in  the  final  product,  from  imperfect  mixing, 
has  often  led  to  the  disintegration  of  the  mortar  by  sea-water,  and  by  fresh 
water  containing  carbonic  acid  in  solution. 

"As  already  stated,  most  American  Portland  cement  is  made  from  argil- 
laceous limestone,  as  shown  by  the  following  table. 

NUMBER   OF    AMERICAN"    CEMENT    FACTORIES    USING    LIMESTONE    COMPARED 
WITH    THE    USERS    OF    MARL    (1894). 


Factories  Using 

Number. 

Quantity. 

Lim6stoii6    

17 

Barrels. 
611  829 

Marl   

7 

186  928 

Total      

24 

798  757 

"The  first  group  includes  G  factories  in  the  Lehigh  County  region  in 
Pennsylvania,  producing  over  400,000  barrels;  1  at  Phillipsburg,  N.  J. ;  and 
10  at  other  points.  The  second  group,  using  marl,  includes  4  factories  in 
New  York,  2  in  Ohio,  and  1  in  Indiana." 

167.  Processes  Used  in  Pulverizing  and  Mixing  the  Raw  Materials.— 
There  are,  in  general,  three  processes  employed  in  preparing  this  intimate 
mixture  of  the  raw  materials,  which  may  be  designated  "  The  Wet  Process/* 
"  The  Semi-wet  Process,"  and  "  The  Dry  Process." 

1.  The  Wet  Process  was  originally  employed  in  England  and  in  France, 
and  was  used  for  the  admixture  of  crushed  chalk  and  clay.  These  were 
pulverized  and  mixed  in  "  wash-mills  "  with  such  an  excess  of  water  as  to 
form  a  thin  liquid.  This  was  stirred  by  such  an  arrangement  as  that  shown 
in  Fig.  82,  the  escape  being  at  the  top  over  a  lip  or  weir.  The  coarsest 
particles  settled  in  this  wash-mill,  and  such  granulated  matter  as  escaped 
in  the  liquid  was  intercepted  on  its  way  to  the  "  backs,"  which  were  open 
tanks  some  four  feet  deep,  with  earth  or  gravel  bottoms.  The  mixture  was 
now  allowed  to  settle  for  some  days,  when  the  clear  water  was  siphoned  off 
and  the  "  slurry"  left  to  dry  in  the  open  air  until  it  could  be  handled  with 
a  shovel.  It  was  then  wheeled  upon  drying-floors  and  dried  by  artificial 
heat  into  irregular  clods  or  masses,  when  it  was  sent  to  the  furnace.  Even 
in  summer  this  process  required  many  weeks'  time  for  its  completion,  and 
in  the  first  settlement  the  chalk  and  clay  ingredients  would  sometimes  have 
a  different  specific  gravity,  and  hence  they  would  not  settle  simultaneously. 
This  would  give  an  uneven  mixture,  which  would  be  so  far  fatal,  since  it 


LIME,   CEMENT,  MORTAR,  AND   CONCRETE. 


193 


could  not  be  corrected.     This  process  is  going  out  of  use  even  for  such 
material  as  is  suited  for  this  method  of  treatment. 

2.  The  Semi-wet  Process  consists  in  mixing  the  ingredients  in  the  state 
of  a  soft  paste.  This  may  be  done  either  by  grinding  them  together  in  this 
condition  or  by  means  of  "edge-runners."  These  consist  of  heavy  cast-iron 
cylinders  of  short  length,  mounted  on  a  horizontal  axle  which  is  made  to- 


FIG.  8-3.—  Wash- mill  used  in  the  Wet  Process  of  making  Portland  Cement. 

swing  about  a  vertical  axis,  thus  causing  the  heavy  cylinder  to  roll  about  on 
a  bed-plate.  Sometimes  the  roller-axle  maintains  a  fixed  position  and  the 
plate  revolves  on  which  it  rests.  This  is  an  efficient  pulverizer  and  mixer 
when  the  ingredients  are  comparatively  soft.  It  does  not  produce  as 
uniform  a  pulverization,  however,  as  a  grinding-mill.  Both  these  processes 
are  used  in  America.* 

3.  The  Dry  Process  is  used  in  Germany,  and  in  Pennsylvania  and  New 
Jersey  in  this  country,  where  the  materials  consist  of  argillaceous  lime- 
stone having  nearly  the  proper  composition  for  making  Portland  cement. 
The  rock  is  first  crushed  and  then  ground.  The  final  mixture  of  limestone 
and  clay-shale  is  made  before  the  material  is  ground,  so  that  the  process  of 
grinding  effects  a  very  thorough  mixing.  The  ingredients  must  be  reduced 
to  an  impalpable  powder  in  order  to  make  possible  that  thorough  mixing 
necessary  to  enable  each  molecule  of  lime  to  associate  itself  with  its  mole- 
cule of  clay  in  the  calcining  process,  so  as  to  produce  the  true  chomical 
combinations  in  the  clinker.  If  the  limestone  used  has  primarily  nearly 
the  composition  required,  which  is  sometimes  the  case  in  America,  then  it 
is  evident  that  any  want  of  perfection  in  the  first  grinding  and  mixing  of 
the  raw  materials  is  not  so  injurious,  since  the  native  mixture  is  not  only 

*  At  Bellefontaine,  O.,  the  "edge-runners"  are  used,  and  at  Sandusky,   O.,  the 
grinding-mill,  the  material  in  both  cases  being  a  soft  marl  and  clay. 


194  THE  MATERIALS  OF  CONSTRUCTION. 

nearly  correct  as  to  proportions,  but  so  far  as  it  goes  the  admixture  is  prac- 
tically perfect.  When  pure  carbonate  of  lime  is  used  (as  in  the  case  of  soft 
marl)  with  clay,  there  is  no  primary  mixture  of  the  lime  and  clay  at  all,  and 
hence  the  necessity  of  a  much  more  elaborate  artificial  mixing  process  than 
when  these  ingredients  are  found  intimately  associated  in  a  natural  rock 
and  to  nearly  the  correct  proportions.  On  the  other  hand,  the  soft  marl 
and  clay  (of  Ohio,  for  instance)  are  much  more  easily  worked  than  the  hard 
limestone  and  clay  shales  (of  Pennsylvania).  In  order  to  enable  the  hard 
materials  to  compete  successfully  with  the  soft,  it  is  necessary  that  the 
limestone  should  contain  primarily  nearly  the  proper  proportion  of  clay. 

After  the  dry  grinding  and  mixing  of  the  raw  materials,  the  dust  is  wet 
sufficiently  and  moulded  into  bricks  (thus  obtaining  a  further  mixing),  and 
then  dried  and  burned.  The  raw  powder  cannot  be  calcined  in  the  ordinary 
furnaces  without  first  compacting  it  in  aggregate  forms  to  allow  of  a  draft 
of  air  through  them.  In  the  tubular  rotating  furnaces  it  is  calcined  as  a 
dry  powder,  and  this  is  one  of  the  great  advantages  of  that  process. 

168.  Processes  Used  in  Burning  Portland  Cement. — "There  are  three 
distinct  forms  of  kiln  used  in  burning  Portland  cement  in  America.  These 
are  (1)  intermittent  or  dome  kiln,  (2)  continuous  kiln,  of  the  Dietzsch  or 
Shofer  type,  (3)  rotary  furnace.  In  the  old-fashioned  intermittent  kiln  the 
bricks  of  cement  mixture  are  charged  into  the  kiln  with  coke  in  alternate 
layers,  and  the  whole  allowed  to  burn  out  and  cool  down  before  emptying. 
The  Dietzsch  or  Shofer  continuous  kiln  is  continuously  charged  with  bricks 
of  cement  mixture  and  soft  coal,  and  the  burned  clinker  periodically  with- 
drawn at  the  bottom.  It  presents  the  great  advantage  of  cheaper  fuel  and 
economy  of  labor,  and  burns  the  dry  powdered  material.  The  rotary  fur- 
nace consists  of  a  rotary  cylinder  heated  by  a  blast  of  air  and  gaseous  fuel, 
the  material  being  continuously  run  in  at  one  end,  and  issuing  as  burned 
clinker  at  the  other.  This  process  was  patented  by  Mr.  Frederick  Ransome, 
in  England,  in  1885,  and  has  been  subsequently  modified  and  improved  by 
others.  Many  difficulties  have  been  met  with  in  carrying  out  this  plan,  but 
it  is  now  successfully  operated  at  a  number  of  works  in  this  country.  It 
would  seem  to  be  the  most  rational  method  of  carrying  on  the  burning  of 
cement,  since  it  effects  an  enormous  saving  in  time  and  labor,  and  allows 
the  temperature  to  be  regulated  far  more  exactly  than  is  possible  in  the 
older  processes.  Crude  or  fuel  oil  is  used  as  a  source  of  heat  at  all  points  in 
America  where  this  kiln  is  employed,  though  producer-gas -with  or  without 
regenerative  furnaces  might  be  employed.* 

"  In  the  United  States  most  of  the  Portland  cement  produced  is  burned  in 
the  old-fashioned  intermittent  kilns.  The  Dietzsch  kiln  is  used  at  Harper 
and  Middle  Branch,  Ohio.  The  Shofer  kiln  is  to  be  used  at  new  works  now 

*  This  process  requires  a  much  greater  fuel  expense  than  the  kilns  and  seems  to  be 
used  only  where  the  raw  material  will  not  adhere  sufficiently  by  wetting  to  form 
briquettes  which  can  be  burned  in  kilns. — J.  B.  J. 


LIME,  CEMENT,  MORTAR,  AND   CONCRETE. 


195 


beginning  operations  at  Glens  Falls,  N.  Y.  The  rotary  furnace  is  in  oper- 
ation at  Colton,  Cal.,  Phillipsburg,  N.  J.,  Coplay,  Pa.,  and  Sandusky, 
Ohio.  The  following  table  shows  the  number  of  barrels  of  cement  made 
during  1894  and  1895  in  vertical  kilns  (continuous  and  intermittent)  and 
the  rotary  furnace. 

AMOUNT   OF   PORTLAND   CEMENT   MADE   IN    KILNS    OF   VARIOUS   KINDS. 


Rotar}r  furnace           

1893. 
Barrels. 
149.000 

1894. 
Barrels. 
242,176 

Vertical  kilns  (continuous  and  intermittent)    .  .  .         

441  653 

556  581 

Total.. 

590,653 

798.757 

It  thus  appears  that  the  output  of  rotary  furnaces  has  increased  much 
more  rapidly  than  that  of  vertical  kilns.  The  recent  rapid  advance  in  the 
price  of  crude  oil  is  a  great  obstacle  to  the  use  of  the  rotary  furnace.  At- 
tempts are  being  made  to  substitute  producer-gas  for  crude  oil  in  burning 
cement.  There  is  no  reason  why  this  should  not  be  successfully  done,  and 
the  change  will  greatly  reduce  the  cost  of 
burning  cement  at  all  points  where  the 
rotary  process  is  used." 

169.  Grinding  the  Clinker. — "  For 
grinding  the  finished  product  the  Griffin 
steel  mill  is  used  at  the  larger  factories. 
Some  of  the  older  works  still  use  buhr_ 
stones.  The  Griffin  mill*  consists  of  a 
steel  ring,  against  the  inside  surface  of 
which  a  heavy  steel  roll  revolving  on  a  ver- 
tical shaft  presses  by  centrifugal  force* 
Fig.  83.  The  mill  is  provided  with  screens 
which  allow  powder  of  the  requisite  fine- 
ness to  pass  through,  while  the  coarser 
particles  drop  back  into  the  mill.  This 
mill  is  an  American  invention,  and  is 
rapidly  finding  its  way  into  the  leading 
cement-works  of  Germany." 


FIG.  83.— Perspective  View  of  the 
Griffin  Mill. 


*  Made  by  the  Bradley  Pulverizer  Co.,  Boston,  Mass.  It  is  used  for  all  kinds  of 
pulverizing  where  buhrstones  and  stamp-mills  have  hitherto  been  employed.  It  works 
in  either  wet  or  dry  material,  and  is  an  extremely  ingenious  and  successful  grinding 
machine. — J.  B.  J. 


CHAPTER  XII. 

THE  MANUFACTURE  OF  VITRIFIED  PAVING-BRICK. 
By  H.  A.  WHEELER,  E.M.* 

170.  Definition. — As  there  is  a  lack  of  harmony  in  the  use  of  the  term 
vitrified  brick,  it  is  necessary  to  define  what  is  meant  by  vitrified.  There 
is  a  popular  idea  that  a  vitrified  brick  must  be  glassy,  in  accordance  with 
the  etymology  of  the  word;  whereas  a  truly  glassy  brick  is  impracticable  to 
make — at  least  to  a  reasonably  large  percentage;  and  unless  annealed  with 
very  much  more  care  than  is  now  given  to  paving-brick,  such  a  brick  would 
be  too  brittle  for  paving  purposes,  besides  being  badly  misshapen.  It  is  true 
that  samples  of  excellent  paving- brick  frequently  exhibit  to  an  eminent 
degree  a  glassy  or  vitreous  surface;  but  these  vitreous  faces  are  due  to  air- 
checks  (caused  by  the  hot  brick  being  struck  by  cold  air),  and  if  the  brick 
is  broken  along  an  unchecked  or  solid  face  it  will  not  exhibit  a  glassy 
surface:  it  will  there  present  a  very  close,  dense,  homogeneous,  stone-like 
.fracture,  and  this  fracture  is  what  is  recognized  and  accepted  as  character- 
istic of  a  vitrified  brick.  There  is  a  total  absence  of  the  individual  parti- 
cles of  the  clay  in  such  a  f lecture  the  presence  of  which  characterizes  build- 
ing and  fire-brick.  Furthermore,  such  a  vitrified  brick  has  a  hardness  of  6.5 
to  7,  on  Moh's  scale  of  hardness,  or  is  about  as  hard  as  quartz  (the  hardest 
mineral  in  granite),  and  it  ..readily  scratches  glass  or  the  hardest  steel.  While 
this  typical  vitrified  fracture  is  easily  recognized  by  the  experienced  eye, 
there  is  no  sharp  line  of  demarcation  between  it  and  the  glassy  fracture 
on  the  one  side  (when  the  brick  is  overturned),  and  a  hard  but  unvitrified 
brick  on  the  other  hand  (when  underlurned)\  for  clay  gradually  passes 
through  a  transition,  when  highly  heated,  from  (1)  an  eminently  porous, 
strong,  and  rather  hard  condition  just  previous  to  tjie  vitrifying-point;  (2) 
to  a  very  much  harder,  tougher,  slightly  porous  condition  when  vitrified; 
and  finally  (3)  to  a  very  dense,  glassy,  non-porous  condition  when  com- 
pletely vitrified,  in  which  latter  condition  it  is  very  apt  to  be  decidedly  brit- 
tle. These  three  stages  of  burning  can  usually  be  found  in  every  kiln  of 
paving-brick,  with  all  intermediate  transitions  from  one  extreme  to  the  other, 

*  Formerly  Assistant  Geologist  Missouri  State  Geological  Survey,,  in  charge  of  inves- 
tigations made  on  clays,  and  now  (1896)  manufacturing  paving-brick  in  St.  Louis,  Mo. 

196 


THE  MANUFACTURE  OF   VITRIFIED  PAVING-BRICK  197 

though  from  60$  to  90$  usually  come  within  the  second  or  properly  vitrified 
stage. 

171.  Clays  employed  for  Paving-brick. — Three  radically  different  classes 
of  clays  are  employed  in  the  manufacture  of  paving-brick,  viz.: 
I.  Surface  Clays; 
II.  Inferior  Fire-clays; 
III.  Shales. 

Surface  Clays. 

By  surface  clays  are  meant  those  soft,  unconsolidated  clays  at  or  near 
the  surface  which  have  been  deposited  during  or  since  the  glacial  period, 
or  that  have  resulted  from  the  atmospheric  decay  of  the  underlying  rocks. 
This  class  of  clays  was  more  frequently  used  in  the  earlier  development 
of  the  paving-brick  industry,  but  they  have  been  almost  completely 
given  up  on  account  of  the  great  difficulty  in  successfully  vitrifying 
a  large  percentage  of  the  brick ;  for,  as  a  rule,  they  are  apt  to  be  so  very 
siliceous  (or  have  from  60$  to  80$  silica),  or  else  so  very  calcareous  (or 
have  from  10$  to  25$  lime),  that  there  is  usually  a  very  narrow  range  of 
temperature  at  which  they  can  be  vitrified.  Hence  the  brick  are  apt  to  be 
either  too  soft  (underburned),  or  else  over  burned  and  badly  misshapen,  so 
that  these  clays  have  been  generally  abandoned  for  the  safer-burning  shales 
and  fire-clays. 

Inferior  Fire-clays. 

The  inferior  or  impure  fire-clays,  which  are  frequently  known  in  the 
trade  as  "  bastard  fire-clay  "  or  "  pipe-clay,"  have  been  quite  largely  used  in 
the  past,  and  are  still  employed  to  some  extent  in  the  manufacture  of 
paving-brick.  They  are  a  class  of  fire-clays  thaT  con  tain  sufficient  fluxing 
impurities  to  enable  them  to  be  slightly  vitrified,  and  the  more  impure 
the  fire-clay  the  more  successfully  it  can  be  used  for  this  purpose.  When 
the  physical  properties  of  the  fire-clay  are  suitable,  these  impure  fire-clays 
make  an  excellent  quality  of  fire-brick,  though  they  always  show  rather 
high  absorption,  or  from  2$  to  5$  of  water  after  soaking  24  hours  in  water. 
They  never  show  a  glassy  fracture,  and  are  rarely  misshapen  or  kiln-marked, 
as  in  the  other  two  classqs  of  clays;  but  they  are  very  much  more  apt  to  be 
soft,  and  therefore  short-lived,  from  underburning,  as  it  requires  a  very  high 
heat  to  vitrify  them.  When  properly  vitrified,  .they  make  a  very  satisfac- 
tory paving-brick,  on  account  of  their  toughness,  and  some  of  the  oldest 
paving-brick  in  the  country  were  made  from  this  class  of  clays,  notwith- 
standing that  they  exhibit  a  very  high  absorption  of  water. 

Shales. 

The  shales,  or  those  hard,  consolidated,  laminated,  rock-like  clays  that 
are  also  popularly  called  "soapstone"  and  "soft  slate,"  are  now  almost 
exclusively  used  in  the  manufacture  of  paving-brick.  They  occur  in  very 


198  THE  MATERIALS   OF  CONSTRUCTION. 

much  larger  and  thicker  bodies  than  either  the  surface  clays  or  fire-clays, 
often  outcropping  as  low  hills,  and  they  can  usually  be  cheaply  worked  by 
steam-shovels  in  open  pits.  While  they  are  usually  non-plastic  as  they 
occur  in  the  bank,  they  can  be  easily  ground  to  powder,  when  they  readily 
work  up  into  a  plastic  mass  with  water.  The  shales  are  usually  very  high 
in  fluxing  impurities,  and  this  is  the  reason  why  they  are  so  favorably 
adapted  for  paving-brick,  as  this  enables  them  to  be  readily  vitrified.  The 
average  composition  of  the  shales  that  have  proved  eminently  satisfactory 
for  this  purpose  is  as  follows: 

Silica  (Si02) 56  per  cent. 

Alumina  (A1203) - , 22       " 

Ignition  loss  (chemically  combined  water).     7       " 

Moisture  (H20) 2       " 

Total  non-fluxing  constituents 87  per  cent. 

Sesquioxide  of  iron  (Fe203) 7  per  cent. 

Lime  (CaO)  1       « 

Magnesia  (MgO) 1       " 

Alkalies  (K2ONa20) 4       « 

Total  fluxing  constituents 13  per  cent. 

Grand  total 100  per  cent. 

While  the  best  shales  range  quite  closely  around  the  preceding  analysis, 
quite  a  range  in  the  fluxing  constituents  is  permissible,  as  the  chemical 
analysis  is  always  very  secondary  in  the  consideration  of  clays.  All  clays, 
for  any  purpose  whatever,  depend  primarily  on  their  physical  properties, 
and  if  these  are  not  favorable  the  chemical  composition  is  of  no  importance. 
A  very  elaborate  discussion  of  the  chemical  composition  and  the  influence 
of  the  impurities  of  clays  is  given  by  the  writer  in  Part  I.  of  the  "Report 
on  the  Missouri  Clays,"  to  which  the  reader  is  referred  for  details  which  it 
is  impossible  to  discuss  in  this  brief  chapter.* 

172.  Physical  Properties  of  Clays. — The  physical  properties  of  clay,  on 
which  depend  its  manufacture  and  uses,  consist  of  the  following  factors : 
I.  Plasticity; 
II.  Shrinkage  in  drying  and  burning; 

III.  Speed  in  drying,  burning,  and  cooling; 

IV.  Point  of  incipient,  complete,  and  viscous  vitrification; 
V.  Density  before  and  after  burning; 

VI.  Colors  of  burned  ware; 
VII.  Strength  of  burned  ware. 

Plasticity. 

Plasticity  is  the  most  important  quality  of  any  clay,  as  its  ability  to  be 
moulded   depends   upon   this   property.      When  mixed   with   the   proper 
*  To  be  obtained  from  the  State  Geologist,  Jefferson  City,  Mo. 


THE  MANUFACTURE  OF  VITRIFIED  PAVING-BRICK.  199 

amount  of  water  it  is  called  fat  when  it  is  very  plastic,  and  the  more 
plastic  the  clay  the  stronger  the  brick  will  be.  In  making  paving-brick, 
excessive  plasticity  is  found  to  increase  the  defect  of  laminations,  which 
is  a  great  source  of  weakness  if  excessively  developed.  To  counteract  this 
trouble  the  clay  is  either  mixed  with  a  less  plastic  one,  or  with  sand,  "  grog," 
or  other  lean  materials  which  reduce  the  plasticity. 

Shrinkage. 

The  shrinkage  is  a  very  important  factor  in  determining  the  size  of 
moulds  and  dies  to  produce  a  given-sized  brick  after  burning.  The  drying 
shrinkage  is  the  reduction  of  volume  which  takes  place  when  the  soft  mud 
brick  becomes  dry  from  the  elimination  of  the  water  used  in  moulding, 
which  amounts  to  3  to  7  per  cent.  A  second  shrinkage  occurs  when  the 
dried  brick  is  burned,  which  is  greater  the  harder  the  brick  is  burned,  until 
thoroughly  vitrified,  when  it  ceases  to  shrink.  The  fire  shrinkage  varies 
from  4  to  8  per  cent,  and  the  total  shrinkage  ranges  from  7  to  15  per  cent. 

Speed  of  Drying,  etc. 

The  speed  of  drying,  burning,  and  cooling  are  extremely  important 
factors  to  the  manufacturer  in  determining  the  size  of  his  plant,  besides 
being  of  great  importance  in  affecting  the  strength  of  the  brick.  Some 
clays  can  be  rapidly  dried,  burned,  and  cooled  without  'having  their  strength 
seriously  impaired,  while  others  are  very  much  weakened,  if  not  actually 
cracked  or  ruptured,  unless  this  is  carried  on  very  slowly.  As  a  broad  rule, 
the  more  plastic  a  clay  the  more  slowly  it  must  be  dried,  burned,  and  cooled, 
while  the  coarser  and  leaner  clays  can  be  treated  much  more  rapidly  with- 
out detriment.  This  is  a  factor  that  is  keenly  appreciated  by  the  manu- 
facturer, but  is  rarely  understood  or  appreciated  by  the  engineer,  yet  it 
affects  the  strength  of  the  brick  more  than  any  one  factor.  It  does  not 
follow  that  a  clay  that  requires  to  be  slowly  dried  must  necessarily  be 
slowly  heated  and  cooled,  or  vice  versa;  for  there  is  an  individuality  about 
clays  that  requires  a  separate  determination  of  each  of  these  factors  as  to 
their  amount  and  influence. 

Vitrification. 

The  stages  of  (1)  incipient,  (2)  complete,  and  (3)  viscous  vitrification 
are  extremely  important,  as  paving-brick  should  be  raised  to  at  least  the 
stage  of  incipient  vitrification  to  secure  the  requisite  density,  hardness,  low 
absorption,  and  toughness;  while  it  must  not  be  raised  to  the  point  of 
viscous  vitrification,  as  it  then  loses  its  shape.  In  the  shales  suitable  for 
paving-brick  the  first  stage  is  reached  at  from  1500°  to  1800°  F.,  and  the 
second  at  1800°  to  2200°  F.,  or  at  a  very  bright  cherry-red. 

Density. 

The  denser  the  clay  the  denser  the  brick  made  therefrom  will  be,  and 
the  higher  the  density  the  more  durable  the  brick.  The  specific  gravity 


200  THE  MATERIALS  OF  CONSTRUCTION. 

of  shales  usually  range  from  2.10  to  2.60,  and  the  specific  gravity  of  the 
brick  will  be  about  the  same.  The  impure  fire-clay  brick  are  generally  some- 
what lighter,  or  vary  from  1.95  to  2.30,  but  the  brick  have  a  specific 
gravity  somewhat  lower  than  that  of  the  original  fire-clay. 

Color. 

The  color  of  paving-brick  is  of  great  local  importance  in  estimating  the 
degree  to  which  it  has  been  burned,  and  the  care  witli  which  it  has  been 
handled.  If  the  shale  is  high  in  iron  (which  is  usually  the  case)  the  result- 
ant brick  varies  from  red  to  very  dark  brown  in  color,  while  if  the  clay  is 
low  in  iron  and  high  in  lime  it  is  light  in  color.  Furthermore,  the  skill 
of  the  burner  is  able  to  largely  influence  the  color  by  the  manipulation  of 
his  fires,  so  that  general  rules  for  determining  the  quality  of  paving-brick 
by  color  only  are  dangerous,  though  for  specific  cases  and  a  given  burner 
they  are  of  very  great  aid  in  quickly  arriving  at  the  quality  of  the  brick. 

THE   MANUFACTURE   OF   PAVING-BRICK. 

173.  Preparing  the  Clays. — The  surface  clays  are  usually  obtained  by 
either  the  pick  and  shovel,  plough  and  scraper  or  clay  gatherer,  or  the 
steam-shovel  and  cars,  according  to  the  size  of  the  yard  and  local  conditions. 
The  fire-clays,  as  they  usually  occur  underground,  are  mined  by  the  room- 
and-pillar  system,  like  coal,  which  is  very  much  more  expensive.  The 
shales  are  sometimes  worked  by  the  room-and-pillar  system,  where  they 
occur  underground,  but  in  most  cases  they  are  worked  in  open  pits,  by 
blasting,  or  else  worked  direct  from  the  bank  into  the  cars  by  powerful 
steam-shovels. 

The  clays  are  sometimes  pulverized  by  toothed  rolls," and  occasionally  by 
centrifugal  disintegrators,  but  in  most  cases  a  revolving  dry-pan  with  a 
perforated  grate  bottom  is  employed  especially  for  shales  and  fire-clays. 

The  crushed  clay  is  usually  screened  in  either  revolving  trommels,  or 
fixed  or  shaking  riddles,  with  4  to  16  meshes  to  the  linear  inch.  The 
degree  of  fineness  of  the  screen  is  a  very  important  matter,  as  the  finer  the 
clay  the  more  plastic  it  is,  and  hence  the  stronger  the  brick.  In  some 
cases,  however,  excessive  fineness  causes  checking  and  cracking  in  drying 
or  burning,  and  aggravates  the  trouble  from  laminations,  so  that  the  fine- 
ness of  the  screen  should  be  determined  for  each  specific  clay.  Sometimes 
the  clay  is  not  screened  any  further  than  is  accomplished  by  the  screen- 
plates  of  the  dry-pan,  which  are  usually  ^  to  ^  inch  in  width. 

The  screened  clay  is  next  mixed  with  water  to  a  more  or  less  plastic 
mass  in  a  pug-mill.  The  pug-mill  consists  of  a  trough  containing  a  revolv- 
ing shaft  that  is  armed  with  blades  set  at  an  angle.  It  should  revolve  at 
such  a  speed,  or  the  blades  should  be  set  at  such  low  pitch,  or  the  length 
should  be  sufficiently  great,  or  the  amount  of  clay  to  be  pugged  should  be 
so  restricted,  as  to  secure  a  thorough,  uniform  mixture  of  the  clay  and 
water;  but  frequently  the  pug-mills  are  too  short  to  accomplish  this,  or  they 


THE  MANUFACTURE  OF   VITRIFIED  PAVING-BRICK.  201 

are  overcrowded,  or  speeded  too  high,  or  the  clay  is  run  through  too  quickly 
by  the  blades  being  given  an  excessive  pitch,  and  consequently  the  clay 
comes  out  with  variable  amounts  of  water.  This  causes  checking  and 
cracking  in  the  drying,  and  sometimes  in  the  burning,  with  marked  varia- 
tions in  the  strength  of  the  brick,  besides  causing  the  bar  of  clay  to  rag  as 
it  leaves  the  brick  machine.  The  more  thoroughly  a  clay  is  pugged,  the 
more  plastic  it  is  rendered,  and  the  more  uniform  and  reliable  will  be  the 
quality  of  the  brick,  and  this  department  could  be  remodelled  to  decided 
advantage  in  most  paving-brick  plants. 

174.  Moulding. — Three  processes  are  employed  for  moulding  paving 
brick,  to  wit: 

The  Soft-mud  Process; 
The  Stiff-mud  Process; 
The  Semi-dry  Process. 

In  tlie  Soft-mud  Process  the  clay  is  mixed  with  sufficient  water  to 
make  a  very  soft,  extremely  plastic  mud,  which  is  moulded  by  hand  or 
soft-mud  machines  into  imperfectly  formed  brick;  these  are  allowed  to 
partially  dry,  to  a  firm,  stiff  condition,  and  are  then  repressed  into  perfectly 
formed  brick.  This  process  makes  an  excellent  quality  of  brick,  but  it 
necessitates  a  second  handling  of  the  brick  during  the  drying  stage.  Out- 
side of  a  few  small  yards,  it  has  been  quite  generally  given  up  in  the  paving- 
brick  trade,  on  account  of  the  expense  of  the  extra  handling  and  breakage, 
besides  considerable  risk  of  injuring  the  strength  of  the  brick,  if  they  arc 
allowed  to  get  too  dry. 

In  the  Stiff -mud  Process  the  clay  is  pugged  with  sufficient  water  to 
make  a  stiff,  plastic  mud,  which  is  forced  through  a  die  by  a  continuous- 
working  auger  or  intermittent  plunger,  as  a  bar  of  clay,  which  is  then  cut 
by  wires  into  suitable  lengths.  This  is  the  process  that  is  almost  univer- 
sally employed  in  the  manufacture  of  vitrified  brick,  as  the  mud  is  stiff 
enough  to  be  made  into  perfectly  shaped  brick,  which  can  be  loaded  on  to 
cars  without  risk  of  being  marked  or  injured  in  handling. 

In  extruding  the  bar  of  clay  from  the  brick  machine,  two  types  of  dies 
are  employed;  in  one  the  bar  of  clay  is -approximately  3"  X  4"  in  section, 
which  is  cut  into  9"  lengths,  and  is  known  as  the  '*  end-cut  system";  while 
in  the  other  the  die  is  approximately  4"  X  9"  in  section,  and  the  bar  is  cut 
into  3"  lengths,  which  is  known  as  the  "side-cut  system."  There  is  con- 
siderable difference  of  opinion  as  to  the  relative  merits  of  these  two  methods 
of  moulding,  which  too  frequently  is  founded  on  very  diversified  facts.  If 
the  clay  is  lean  or  sandy,  the  side-cut  brick  is  apt  to  be  of  better  quality 
than  the  end-cut;  while  if  the  clay  is  very  fine  and  eminently  plastic,  the 
end-cut  system  gives  fewer  laminations  and  a  superior  quality  to  the  side- 
cut. 

In  the  Semi-dry  Process  the  clay  is  mixed  with  just  enough  water  to 
dampen  it,  so  that  it  adheres  slightly  when  firmly  pressed.  The  brick  are 


202  THE  MATERIALS  OF  CONSTRUCTION. 

moulded  by  feeding  the  damp  clay  into  a  mould-box,  in  which  it  is  sub- 
jected to  a  very  heavy  pressure  by  a  reciprocating  plunger.  This  process 
has  been  used  to  a  very  limited  extent  for  paving-brick,  as  the  brick  are 
not  as  tough  as  when  made  by  the  mud  process,  while  it  is  much  more 
difficult  to  burn  a  large  percentage  of  No.  1  grade.  As  there  is  consid- 
erable difficulty  in  feeding  the  mould-boxes  with  damp  clay,  the  mouids 
are  frequently  only  imperfectly  filled,  which  prevents  the  brick  from 
receiving  the  heavy  pressure  necessary  to  bond  it,  besides  causing  imperfect 
faces. 

Repressing. — Kecently  there  has  been  a  heavy  demand  for  repressing 
the  brick  made  by  the  stiff-mud  process  immediately  after  it  leaves  the 
brick  machine.  In  the  repressing  process  the  brick  is  exposed  to  a  mod- 
erate vertical  pressure  in  a  metal  mould-box,  while  still  in  a  plastic  condi- 
tion, which  thoroughly  fills  out  the  edges  and  angles,  and  rounds  them  if 
desired.  This  results  in  a  brick  of  uniform  size  and  perfect  shape,  so  that 
the  appearance  of  the  brick  is  greatly  improved  ;  but  as  the  pressure  is 
moderate,  it  is  doubtful  if  the  quality  of  the  brick  is  enhanced  by  this 
extra  operation.  Where  there  have  been  opportunities  for  testing  the 
relative  merits  of  the  same  clay  in  repressed  and  unrepressed  brick,  the 
facts  indicate  that  the  strength  of  the  brick  is  endangered  by  breaking  the 
structure  formed  in  the  slow-acting  brick-machine  by  subjecting  it  to  such" 
radically  different  forces  as  occur  in  a  vertical-acting,  quickly  applied 
repress.  Thus  some  Purington  unrepressed  brick  have  been  exposed  for 
two  years  on  Lasalle  Street,  Chicago,  to  the  heaviest  kind  of  metropolitan 
traffic,  which  it  has  very  successfully  withstood;  while  repressed  brick 
from  the  same  plant  has  not  stood  so  well  on  other  Chicago  streets  with 
much  less  traffic.  This  is  a  matter  that  needs  further  investigation  and 
more  facts,  and  the  above  is  the  most  important  evidence  known  to  the 
writer  that  bears  directly  on  this  question.  * 

175.  Drying  and  Burning. — Drying. — The  moulded  brick  are  hacked 
on  cars,  in  open  checkerwork,  direct  from  the  brick-machine,  which  are  run 
in  drying-tunnels,  where  they  are  exposed  for  24  to  60  hours  to  light  open 
fires,  or  to  a  heated  blast,  or  to  the  radiation  of  an  extensive  series  of  steam- 
pipes,  in  order  to  expel  the  water  used  in  moulding.  Some  clays  can  be 
safely  dried  in  18  to  30  hours  without  checking  or  cracking,  while  others 
have  their  strength  seriously  impaired  unless  the  drying  takes  from  48  to 
72  hours.  Usually  the  finer  and  more  plastic  the  clay  the  greater  the  time 
required,  while  the  coarser  and  leaner  the  cl^y  the  more  rapidly  it  can  be 
dried. 

Burning. — Three  classes  of  kilns  are  employed  in  burning:  the  up- 
draught,  the  down-draught,  and  the  continuous.  The  up-draught  kiln, 
which  is  the  type  usually  employed  in  burning  building-brick,  has  a  series 
of  parallel  fires  at  the  bottom  of  the  kiln,  from  which  the  heat  rises  through 
the  brick,  and  escapes  at  the  top  of  the  kiln.  The  brick  that  are  directly 
exposed  to  the  fire  at  the  bottom  receive  too  mmh  heat,  while  the  brick  at 

*  Recent  (1896)  rattler  tests  by  Prof  Orion,  on  bricks  made  from  the  same  clay,  on 
different  machines,  and  burned  together  in  the  same  kiln,  indicate  clearly  that  repress- 
ing an  end-cut  brick  benefits  it,  while  repressing  a  side-cut  brick  injures  it. 


THE  MANUFACTURE  OF   VITRIFIED  PAVING-BRICK.  203 

the  top  of  the  kiln  do  not  receive  sufficient  heat  to  vitrify  them.  There 
is,  consequently,  a  goodly  percentage  of  overburned,  misshapen  brick  at  the 
bottom  of  the  kiln,  and  a  heavy  percentage  of  soft,  unburned  brick  at  the 
top,  the  central  portion  being  the  only  part  that  receives  the  proper  degree 
of  heat.  As  the  percentage  of  No.  1  brick,  or  those  suitable  for  paving, 
ranges  from  35  to  65  per  cent,  according  to  the  skill  of  the  burner,  the  tip- 
draught  type  of  kiln  is  seldom  employed  for  paving-brick.  In  the  down- 
draught  type  of  kiln  the  heat  rises  to  the  top  or  crown  of  the  kiln  from  a 
series  of  outside  fires,  and  then  passes  down  through  the  brick  to  fines  at 
the  bottom  of  the  kiln,  and  then  escapes  to  one  or  more  stacks.  The  brick 
are  protected  from  excessive  heat,  and  the  heat  is  more  thoroughly  and 
completely  distributed  through  the  brick  than  in  the  up-draught  type.  The 
percentage  of  first-class  brick  is  therefore  much  greater,  as  with  intelligent 
handling  from  CO  to  90  per  cent  of  No.  1  pavers  can  be  obtained. 

The  down-draught  kilns  were  formerly  of  the  round  or  beehive  type, 
which  hold  from  25,000  to  75,000  brick;  but  in  recent  practice  the  long 
rectangular  design  is  preferred,  which  hold  from  100,000  to  300,000  brick, 
and  most  of  the  paving-brick  are  burned  to-day  in  kilns  of  this  design. 

In  -the  continuous  type  of  kiln  the  coal  is  fed  directly  in  among  the  brick, 
which  are  piled  in  a  long  tunnel,  and  the  heat  is  drawn  through  them  by  a 
high  stack  at  the  opposite  end.  This  results  in  a  great  economy  of  fuel 
over  both  the  up-draught  and  down-draught  types  of  kiln;  but  the  shrinkage 
and  the  difficulty  of  securing  uniformity  in  burning  is  so  great  that  they 
only  yield  from  40  to  70  per  cent  of  No.  1  pavers,  and  they  are  not  generally 
used. 

The  practice  of  glazing  paving-brick  with  salt,  similar  to  sewer-pipe,  was 
formerly  employed  to  a  considerable  extent,  as  it  gave  the  brick  a  dark  color, 
which  was  supposed  to  indicate  hardness,  besides  rendering  defects  less  con- 
spicuous. As  the  glaze  is  superficial,  it  adds  nothing  to  the  durability  of 
the  brick,  while  it  greatly  increases  the  difficulty  of  sorting  by  color,  and 
enables  soft  brick  to  be  overlooked  unless  very  thoroughly  inspected.  The 
practice  is  to  be  strongly  deprecated,  and  it  is  dying  out. 

176.  Annealing. — After  the  brick  have  been  burned,  the  kiln  should  be 
tightly  closed  to  shut  off  the  access  of  cold  air,  and  the  longer  the  time  given 
the  brick  to  cool  and  anneal  the  tougher  the  brick  will  be.  Bricks  made 
from  the  best  clays  can  be  ruined  by  cooling  off  the  kiln  too  rapidly.  If 
this  does  not  result  in  checking  the  brick  it  will  at  least  make  them  brittle. 
The  conductivity  of  clay  for  heat  is  so  feeble  that  unless  the  brick  are 
very  slowly  cooled  internal  stresses  are  produced — very  much  as  in  rapidly 
cooled  steel  or  glass— which  interfere  with  the  toughness  of  the  brick. 
This  annealing  or  toughening  by  slow  cooling  is  not  appreciated  by 
engineers,  though  well  understood  by  the  brickmakers.  They  claim  they 
cannot  afford  to  take  the  time  in  cooling  off  the  kilns  that  they  would  like 
to.  where  the  price  is  the  criterion  that  will  determine  the  successful  bidder, 
while  quality  is  made  subordinate.  The  kilns  are  the  most  expensive  portion 


204  THE  MATERIALS  OF  CONSTRUCTION. 

in  a  paving-brick  plant,  and  delay  in  emptying  them  by  slow  cooling  adds 
considerably  to  the  expense  of  manufacture;  so  that  unless  the  brick- 
makers  are  paid  accordingly,  they  cannot  afford  to  anneal  with  the  care 
that  is  demanded  for  the  best  quality  of  brick.  The  usual  practice  in 
brickyards  is  to  "  turn  "  or  fill  a  kiln  once  a  month,  which  allows  from  six 
to  nine  days  for  cooling  off.  If  the  kiln  capacity  of  a  yard  could  be  in- 
creased 25  per  cent  so  as  to  give  the  kilns  twice  the  time  to  cool  off,  it 
would  result  in  a  very  much  tougher,  more  uniform,  and  reliable  brick; 
but  it  would  necessitate  a  price  commensurate  with  this  increased  outlay 
of  capital,  as  there  would  be  no  increase  in  the  quantity  of  brick  produced. 

Where  the  very  best  quality  of  paving-brick  is  required,  a  matter  of  $1.00 
or  $2.00  increase  in  the  cost  of  the  brick  to  insure  thorough  annealing  would 
prove  to  be  very  great  economy,  and  a  very  judicious  investment,  in  greatly 
increasing  the  durability  of  the  pavement. 

177.  Sorting. — In  emptying  the  kiln  there  are  usually  three  grades  of 
brick  made  in  the  vitrified  trade.  In  the  down-draught  type  of  kiln,  one  or 
two  top  courses  are  liable  to  be  air-checked  and  more  or  less  brittle  if  the 
kiln  is  either  improperly  designed  or  improperly  handled  in  burning,  while- r 
the  top  layer  is  always  covered  with  soot  and  ashes  that  mars  and  stains  the 
surface  of  the  brick.  As  these  brick  get  the  highest  heat  they  are  usually, 
the  hardest,  and  while  not  generally  tough  enough  for  paving  purposes,  they 
are  very  desirable  brick  for  sewers,  foundations,  and  sidewalks,  especially  as 
they  are  free  from  kiln-marks,  and  are  seldom  misshapen.  The  first  two  or 
three  layers  are  therefore  usually  set  aside  and  sold  as  sewer  and  sidewalk 
brick. 

The  bottom  portion  of  the  kiln,  or  the  lower  two  to  ten  courses,  do  not 
usually  receive  sufficient  beat  to  be  properly  vitrified,  and  are  known  as  No. 
2  or  building  brick,  as  they  are  well  adapted  for  foundations  or  for  backing- 
stock  brick. 

The  intermediate  or  central  portion  of  the  kiln  are  No.  1,  or  strictly 
first-class,  paving-brick,  which  are  distinguished  by  the  fracture,  toughness, 
hardness,  and  the  color  from  the  other  two  grades  of  brick.  They  should  be 
perfectly  uniform  on  the  fracture,  homogeneous,  very  dense,  very  hard, 
tough,  and  reasonably  free  from  "  kiln-marks,"  or  indentations  made  by 
overlying  brick. 

Kiln-marks  are  a  splendid  guide  that  the  brick  have  received  sufficient 
heat  to  vitrify  them,  and  the  greater  the  depth  of  the  kiln-mark  the  more 
thoroughly  the  brick  is  usually  vitrified;  but  if  too  deep  they  make  a  rough, 
uneven  pavement.  There  is  usually  a  limit  as  to  what  is  allowable  for  the 
depth  of  the  kiln-mark,  which  is  a  matter  of  opinion  for  the  engineer,  and 
is  placed  at  ^  to  f  inch.  Except  in  fire-clays,  it  is  seldom  that  a  properly 
vitrified  brick  is  entirely  free  from  slight  indentations,  unless  from  the 
very  top  of  the  kiln;  with  the  exception  of  this  one  place,  a  total  absence  of 
such  marks  is  apt  to  indicate  underburning. 


CHAPTER  XIII. 
TIMBER.* 

CHARACTERISTICS   AND   PROPERTIES   OF   WOOD. 

178.  Structure  and  Appearance. — The  structure  of  wood  affords  the  only 
reliable  means  of  distinguishing  the  different  kinds.  Color,  weight,  smell, 
and  other  appearances,  which  are  often  direct  or  indirect  results  of  struc- 
ture, may  be  helpful  in  this  distinction,  but  cannot  be  relied  upon  entirely. 
In  addition,  structure  underlies  nearly  all  the  technical  properties  of  this 
important  product  and  furnishes  an  explanation  why  one  piece  differs  as  to 
these  properties  from  another. 

StTucture  explains  why  oak  is  heavier,  stronger,  and  tougher  than  pine; 
why  it  is  harder  to  saw  and  plane,  and  why  it  is  so  much  more  difficult  to 
season  without  injury.  From  its  less  porous  structure  alone,  it  is  evident 
that  a  piece  of  a  young  and  thrifty  oak  is  stronger  than  the  porous  wood  of 
an  old  or  stunted  tree  ;  or  that  Georgia  or  long-leaf  pine  excels  white  pine 
'ii  weight  and  strength.  Keeping  especially  in  mind  the  arrangement  and 
direction  of  the  fibres  of  wood,  it  is  clear  at  once  why  knots  and  "  cross- 
grains  "  interfere  with  the  strength  of  timber. 

It  is  due  to  structural  peculiarities  that  "  honeycombing "  occurs  in 
rapid  seasoning,  that  "checks  "or  cracks  extend  radially  and  follow  pith- 
rays,  that  tangent  or  "bastard"  boards  shrink  and  warp  more  than  quar- 
tered lumber.  These  same  peculiarities  enable  cherry  and  oak  to  take  a 
better  finish  than  basswood  or  coarse-grained  pine. 

Moreover,  structure,  aided  by  color,  determines  the  beauty  of  wood. 
All  the  pleasing  figures,  whether  in  a  hard-pine  ceiling,  a  desk  of  quar- 
tered oak,  or  in  the  beautiful  panels  of  "curly  "or  "bird's-eye"  maple 
decorating  the  saloon  of  a  ship  or  a  palace-car,  are  due  to  differences  in  the 
structure  of  the  wood.  Knowing  this,  the  appearance  of  any  particular 


*  This  chapter  is  taken  from  Bulletin  10  of  the  U.  S.  Forestry  Division,  Agricultural 
Department' 1895  ;  B.  E.  Feruow,  Chief  of  the  Division.  The  matter  contained  in  this 
bulletin  U  ijiiostly  the  result  of  original  studies  made  by  Mr.  Filibert  Roth,  this  work 
beiug  one  c'/epartuient  of  the  "  U.  S.  Timber  Investigations." 

205 


206  THE  MATERIALS  OF  CONSTRUCTION. 

section  can  be  foretold,  and  almost  unlimited  choice  and  combination  are 
thereby  suggested. 

Thus  a  knowledge  of  structure  not  only  enables  us  to  distinguish  the 
different  woods,  judge  as  to  their  qualities,  and  explain  the  causes  of  their 
beauty,  but  it  also  becomes  an  invaluable  aid  to  the  thoughtful  worker, 
guiding  him  to  a  more  careful  selection  and  a  more  perfect  use  of  his 
material. 

179.  Classes  of  Trees. — The  timber  of  the  United  States  is  famished 
by  three  well-defined  classes  of  trees:  the  needle-leaved,  naked-seeded  coni- 
fers (pine,  cedar,  etc.);  the  dicotyledonous  (with  two  seed-leaves),  broad- 
leaved  trees  (oak,  poplar,  etc.)  ;  and  to  an  inferior  extent  by  the  monocoty- 
ledonous  (with  one  seed-leaf),  palms,  yuccas,  and  their  allies,  which  last  are 
confined  to  the  most  southern  parts  of  the  country. 

Broad-leaved  trees  are  also  known  as  deciduous  trees,  although,  es- 
pecially in  warm  countries,  many  of  them  are  evergreen,*  while  the  coni- 
fers are  commonly  termed  "evergreens/'  although  the  larch,  bald  cypress, 
and  others  shed  their  leaves  every  fall,  and  even  the  names  "  broad-leaved  " 
and  "coniferous/'  though  perhaps  the  most  satisfactory,  are  not  at  all 
exact,  for  the  conifer  ginkgo  has  broad  leaves  and  bears  no  cones. 

In  the  lumber  trade,  the  woods  of  broad-leaved  trees  are  known  as 
*'  hardwoods,"  though  poplar  is  as  soft  as  pine,  and  the  coniferous  woods 
are  "  soft  woods,"  notwithstanding  that  yew  ranks  high  in  hardness  even 
when  compared  to  "  hardwoods." 

Both  in  the  number  of  different  kinds  of  trees  or  species  and  still 
more  in  the  importance  of  their  product  the  conifers  and  broad-leaved  trees 
far  excel  the  palms  and  their  relatives. 

In  the  manner  of  growth  both  conifers  and  broad-leaved  trees  behave 
alike,  adding  each  year  a  new  layer  of  wood  which  covers  the  old  wood  in 
all  parts  of  the  stem  and  limbs.  Thus  the  trunk  continues  to  grow  in 
thickness  throughout  the  life  of  the  tree  by  additions  (annual  rings)  which 
in  temperate  climates  are,  barring  accidents,  accurate  records  of  the  tree. 
With  the  palms  and  their  relatives  the  stem  remains  generally  of  the  same 
diameter,  the  tree  of  a  hundred  years  being  no  thicker  than  it  was  at  ten 
years,  the  growth  of  these  being  only  at  the  top.  Even  where  a  peripheral 
increase  takes  place,  as  in  the  yuccas,  the  wood  is  not  laid  on  in  well- 
defined  layers;  the  structure  remains  irregular  throughout. 

Though  alike  in  their  manner  of  growth,  and  therefore  similar  in  their 
general  make-up,  conifers  and  broad -leaved  trees  differ  markedly  in  the  de- 
tails of  their  structure  and  the  character  of  their  wood.  The  wood  of  all 
conifers  is  very  simple  in  its  structure,  the  fibres  composing  tjie  main  part 
of  the  wood  being  all  alike  and  their  arrangement  regular!  The  wood  of 
broad-leaved  trees  is  complex  in  structure;  it  is  made  up  of  several  differ- 

V 
*  In  CeylOn  even  the  cultivated  cherry  has  become  an  evergreen^ 


TIMBER. 

ent  kinds  of  cells  and  fibres  and  lacks  the  regularity  of  arrangement  so 
noticeable  in  the  conifers.  This  difference  is  so  great  that  in  a  study  of 
wood  structure  it  is  best  to  consider  the  two  kinds  separately. 

180.  Sapwood  and  Heartwood. — Examining  a  smooth  cross-section  or 
end  face  of  a  well-grown  log  of  Georgia  pine  or  Norway  pine,  we  distin- 
guish an  envelope  of  reddish,  scaly  bark,  a  small  whitish  pith  at  the  centre, 
and  between  these  the  wood  in  a  great  number  of  concentric  rings. 

A  zone  of  wood  next  to  the  bark,  1  to  3  or  more  inches  wide,  and  con- 
taining thirty  to  fifty  or  more  annual  rings,  is  of  lighter  color;  this  is  the' 
sa^wood,  the  inner,  darker  part  of  the  log  beirig  the  heartwood.  In  the 
former  many  cells  are  active  and  store  up  starch  and  otherwise  assist  in 
the  life-processes  of  the  tree,  although  only  the  last  or  outer  layer  of  cells 
(the  cambium  layer)  forms  the  growing  part  and  the  true  life  of  the  tree. 
In  the  heartwood  all  cells  are  lifeless  cases,  and  serve  only  the  mechanical 
function  of  keeping  the  tree  from  breaking  under  its  own  great  weight,  or 
from  being  broken  by  the  winds. 

The  darker  color  of  the  heartwood  is  due  to  infiltration  of  chemical  sub- 
stances into  the  cell-walls,  but  the  cavities  of  the  cells  in  pine  are  not  filled 
up,  as  is  sometimes  believed,  nor  do  their  walls  grow  thicker,  nor  is  their 
wall  any  more  lignified  than  in  the  sapwood.  Sapwood  varies  in  width  and 
in  the  number  of  rings  which  it  contains,  even  in  different  parts  of  the 
same  tree;  the  same  year's  growth  which  is  sapwood  in  one  part  of  a  disk 
may  be  heartwood  in  another.  Sapwood  is  widest  in  the  main  part  of 
the  stem  and  varies  often  within  considerable  limits,  and  without  apparent 
regularity.  Generally  it  becomes  narrower  toward  the  top  and  in  the 
limbs,  its  width  varying  with  the  diameter,  and  being  least,  in  a  given  disk, 
on  the  side  which  has  the  shortest  radius.  Sapwood  of  old  and  stunted 
pines  is  composed  of  more  rings  than  that  of  young  and  thrifty  specimens. 
Thus  in  a  pine  two  hundred  and  fifty  years  old,  a  layer  of  wood  or  annual 
ring  does  not  change  from  sapwood  to  heartwood  until  seventy  or  eighty 
years  after  it  is  formed,  while  in  a  tree  one  hundred  years  old,  or  less,  it 
remains  sapwood  only  from  thirty  to  sixty  years.  The  width  of  the  sap- 
wood  varies  considerably  for  different  kinds  of  pines;  it  is  small  for  long- 
leaf  and  white  pine,  and  great  for  loblolly  and  Norway  pines.  Occupying 
the  peripheral  part  of  the  trunk,  the  proportion  which  it  forms  of  the 
entire  mass  of  the  stem  is  always  great.  Thus  even  in  old  trees  of  long-leaf 
pine  the  sapwood  forms  about  40  per  cent  of  the  merchantable  log,  while 
in  the  loblolly  and  in  all  young  trees  the  bulk  of  the  wood  is  sapwood. 

181.  The   Annual    Rings. — The    concentric,   annual,   or    yearly,   rings 
which  appear  on  the  end  face  of  a  log  are  cross-sections  of  so  many  thin 
layers  of  wood.     Each  such  layer   forms   an   envelope   around  its   inner 
neighbor,  and  is  in  turn  covered  by  the  adjoining  layer  without,  so  that 
the  whole  stem  is  built  up  of  a  series  of  thin  hollow  cylinders,- or  rather 
cones.     A  new  layer  of  wood  is  formed  each  season,  covering  the  entire 


208  THE  MATERIALS  OF  CONSTRUCTION 

stem,  as  well  as  all  the  living  branches.  The  thickness  of  this  layer,  or 
the  width  of  the  yearly  ring,  varies  greatly  in  different  trees  and  also  in 
different  parts  of  the  same  tree.  In  a  normally  grown,  thrifty  pine  log 
the  rings  are  widest  near  the  pith,  growing  more  and  more  narrow 
toward  the  bark.  Thus  the  central  twenty  rings  in  a  disk  of  an  old 
long-leaf  pine  may  each  be  one-eighth  to  one-sixth  inch  (3  to  4  mm.)  wide, 
while  the  twenty  rings  next  to  the  barK  may  average  only  one-thirtieth 
inch  (0.8  mm.).  In  our  forest  trees  rings  of  one-half  inch  in  width  occur 
only  near  the  centre  in  disks  of  very  thrifty  trees  of  both  conifers  and  hard 
woods;  one-twelfth  inch  represents  good  thrifty  growth,  and  the  minimum 
width  of  about  one'two-hundredths  inch  (0.12  mm.)  is  often  seen  in  stunted 
spruce  and  pine.  The  average  width  of  rings  in  well-grown  old  white  pine 
will  vary  from  one-twelfth  to  one-eighteenth  inch,  while  in  the  slower  grow- 
ing long-leaf  pine  it  may  be  one  twenty-fifth  to  one  fiftieth  of  an  inch. 
The  same  layer  of  wood  is  widest  near  the  stump  in  very  thrifty  young 
trees,  especially  if  grown  in  the  open  part,  but  in  old  forest  trees  the  same 
year's  growth  is  wider  in  the  upper  part  of  the  tree,  being  narrowest  near 
the  stump  and  often  also  near  the  very  tip  of  the  stem.  Generally  the 
rings  are  widest  near  the  centre,  growing  narrower  towards  the  bark.  In 
logs  from  stunted  trees  the  order  is  often  reversed,  the  interior  rings  being 
thin  and  the  outer  rings  widest.  Frequently,  too,  zones  or  bands  of  very 
narrow  rings,  representing  unfavorable  periods  of  growth,  disturb  the 
general  regularity.  Few  trees,  even  among  pines,  furnish  logs  with  truly- 
circular  cross-sections;  usually  they  are  oval,  and  at  the  stump  commonly 
quite  irregular  in  figure.  Moreover,  even  in  very  regular  or  circular  disks 
the  pith  is  rarely  in  the  centre,  and  frequently  one  radius  is  conspicuously 
longer  than  its  opposite,  the  width  of  some  of  the  rings,  if  not  all,  being 
greater  on  one  side  than  on  the  other.  This  is  nearly  always  so  in  the 
limbs,  the  lower  radius  exceeding  the  upper. 

In  extreme  cases,  especially  in  the  limbs,  a  ring  is  frequently  conspicuous 
on  one  side  and  almost  or  entirely  lost  to  view  on  the  other.  Where  the 
rings  are  extremely  narrow,  the  dark  portion  of  the  ring  is  often  wanting, 
the  color  being  quite  uniform  and  light.  The  greater  regularity  or  irregu- 
larity of  the  annual  rings  has  much  to  do  with  the  technical  qualities  of 
the  timber. 

182.  Spring  and  Summer  Wood  (Coniferous  Trees}. — Examining  the 
rings  more  closely,  it  is  noticed  tha.  each  ring  is  made  up  of  an  inner, 
softer,  light-colored,  and  an  niter,  or  peripheral,  firmer  and  darker-colored 
portion.  Being  formed  in  the  fore  part  of  the  season,  the  inner,  light- 
colored  part  is  termed  spring  wood,  the  outer,  darker  portion  being  the 
summer  wood  of  the  ring.  Since  the  latter  is  very  heavy  and  firm,  it  de- 
termines to  a  large  extent  the  weight  and  strength  of  the  wood,  and  as  its 
darker  color  influences  the  shade  of  color  of  the  entire  piece  of  wood,  this 
color  effect  becomes  a  valuable  aid  in -.distinguishing  heavy  and  strong 


TIMBER.  209 


from  light  and  soft  pine  wood.  In  most  hard  pines,  like  the  long-leaf, 
the  dark  summer  wood  appears  as  a  distinct  band,  so  that  the  yearly 
ring  is  composed  of  two  sharply  defined  bands— an  inner,  the  spring  wood, 
and  an  outer,  the  summer  wood.  But  in  some  cases,  even  in  hard  pines, 
and  normally  in  the  wood  of  white  pines,  the  spring  wood  passes  gradually 
into  the  darker  summer  wood,  so  that  a  sharply  defined  line  occurs  only 
where  the  spring  wood  of  one  ring  abuts  against  the  summer  wood  of 
the  previous  year's  growth.  It  is  this  clearly  defined  line  which  en- 
ables the  eye  to  distinguish  even  the  very  narrow  rings  in  old  pines 
and  spruces.  In  some  cases,  especially  in  the  trunks  of  Southern  pines, 
and  normally  on  the  lower  side  of  pine  limbs,  there  occur  dark  bands  of 
wood  in  the  spring-wood  portion  of  the  ring,  giving  rise  to  false  rings 
which  mislead  in  a  superficial  counting  of  rings.  In  the  disks  cut  from 
limbs  these  dark  bands  often  occupy  the  greater  part  of  the  ring  and  appear 
as  "lunes"  or  sickle-shaped  figures.  The  wood  of  these  dark  bands  is 
similar  to  that  of  the  true  summer  wood — the  cells  have  thick  walls,  but 
usually  lack  the  compressed  or  flattened  form. 

Normally,  the  summer  wood  forms  a  greater  proportion  of  the  ring  in 
the  part  of  the  tree  formed  during  the  period  of  thriftiest  growth.  In  an 
old  tree  this  proportion  is  very  small  in  the  first  two  to  five  rings  about  the- 
pith,  and  also  in  the  part  next  to  the  bark,  the  intermediate  part  showing 
a  greater  proportion  of  summer  wood.  It  is  also  greatest  in  a  disk  taken 
from  near  the  stump  and  decreases  upward  in  the  stem,  thus  fully  account- 
ing for  the  difference  in  weight  and  firmness  of  the  wood  of  these  different 
parts.  In  the  long-leaf  pine  the  more  substantial  summer  wood  often  forms 
scarcely  10  per  cent  of  the  wood  in  the  central  five  rings;  40  to  50  per  cent 
of  the  next  one  hundred  rings;  about  30 -per  cent  in  the  next  fifty,  and 
only  about  20  per  cent  in  the  fifty  rings  next  to  the  bark.  It  averages  45 
per  cent  of  the  wood  of  the  stump  and  only  2-4  per  cent  of  tl]at  of  the  top. 

Sawing  the  log  into  boards,  the  yearly  rings  are  represented  on  the  faces 
of  the  middle  board  (radial  sections)  by  narrow,  parallel  stripes  (see  Fig.  84), 
an  inner,  lighter  stripe,  and  its  outer,  darker  neighbor,  always  corres- 
ponding to  one  annual  ring. 

On  the  faces  of  the  boards  nearest  the  slab  (tangential  or  "bastard" 
boards)  the  several  years'  growth  should  also  appear  as  parallel  but  much 
broader  stripes.  This  they  do  only  if  the  log  is  short  and  very  perfect. 
Usually  a  variety  of  pleasing  patterns  is  displayed  on  the  boards,  depend- 
ing on  the  position  of  the  saw-cut  and  on  the  regularity  of  growth  of 
the  log.  (See  Fig.  84!) 

Where  the  cut  passes  through  a  prominence  (bump  or  crook)  of  the  log, 
irregular,  concentric  circlets  and  ovals  are  produced,  and  on  almost  all 
tangent  boards  V-shaped  forms  occur. 

183.  Anatomical  Structure  of  Coniferous  Woods.— Holding  a  well- 
smoothed  disk  or  cross-section  one-eighth  inch  thick  toward  the  light,  it  is 


210 


THE  MATERIALS  OF  CONSTRUCTION. 


readily  seen  that  pine  wood  is  a  very  porous  structure.  If  viewed  with  a 
strong  magnifier,  the  little  tubes,  especially  in  the  spring-wood  of  the  rings, 
are  easily  distinguished  and  their  arrangement  in  regular  straight  radial 
rows  is  apparent.  Scattered  through  the  summer-wood  portion  of  the  rings, 
numerous  irregular  grayish  dots  (the  resin-ducts)  disturb  the  uniformity 
and  regularity  of  the  structure.  Magnified  one  hundred  times,  a  piece  of 
spruce,  which  is  similar  to  pine,  presents  a  picture  like  that  shown  in  Fig. 
85.  Only  short  pieces  of  the  tubes  or  cells  of  which  the  wood  is  com- 
posed are  represented  in  the  picture. 


FIG.  85.— Wood  of  Spruce. 


FIG.  84.— Board  of  Pine.  C8,  cross-section  ; 
US,  radial  section  ;  TS,  tangential  section  ; 
sw,  summer  wood  ;  spw,  spring  wood.* 


1,  natural   size; 

2,  small  part  of  one  ring  magnified  100 
times.  The  vertical  tubes  are  wood- fibres, 
in  this  case  all  "  tracheids."  m,  medullary 
or  pith  ray;  n,  transverse  tracheids  or  pith- 
ray;  a,  b,  and  c,  bordered  pits  of  the  tra- 
cheids, more  enlarged. 


The  total  length  of  these  fibres  is  one-twentieth  to  one-fifth  inch,  being 
smallest  near  the  pith,  and  is  fifty  to  one  hundred  times  as  great  as  their 
width  (Fig.  86).  They  are  tapered  and  closed  at  their  ends,  polygonal  or 
rounded  and  thin-walled,  with  a  large  cavity  (lumen)  or  internal  space  in 
the  spring  wood,  while  they  are  thick-walled  and  flattened  radially,  with  the 
internal  space  or  lumen  much  reduced,  in  the  summer  wood.  (See  right-hand 
portion  of  Fig.  85.)  This  flattening,  together  with  the  thicker  walls  of  the 
cells  which  reduces  the  lumen,  produces  the  greater  firmness  and  darker 

*  This  figure  is  deceptive  inasmuch  as  the  more  open  or  porous  spring  wood  is  repre- 
sented by  a  plain  white  surface,  as  though  it  were  solid,  while  the  more  solid  summer 
wood  is  represented  by  a  shaded  surface  as  though  it  were  more  porous.  The  reverse  is 
of  course  the  case. — J.  B.  J. 


TIMBER. 


211 


mr. 


color  of  the  summer  wood ;  that  is  to  say,  there  is  more 
material  in  the  same  volume.  As  shown  in  the  figure,, 
the  tubes,  cells,  or  "  tracheids  "are  decorated  on  their 
walls  by  circlet-like  structures,  called  "  bordered  pits/' 
sections  of  which  are  seen  more  magnified  at  a,  b,  and 
c,  Fig.  85.  These  pits  are  in  the  nature  of  pores,  cov- 
ered by  very  thin  membranes,  and  serve  as  waterways 
between  the  cells  or  tracheids. 

The  dark  lines  on  the  side  of  the  smaller  piece  (lr 
Fig.  85)  appear  when  magnified  (in  2,  Fig.  85)  as  tiers 
of  eight  to  ten  rows  of  cells,  lying  in  vertical  radial 
planes,  and  are  seen  as  bands  on  the  radial  face,  and  as 
rows  of  pores  on  the  tagential  face.  These  kinds  or 
tiers  of  cell-rows  are  the  "  medullary  rays  "  or  "pith- 
rays,"  and  are  common  to  all  our  lumber  woods.  In 
the  pines  and  other  conifers  they  are  quite  small,  but 
they  can  readily  be  seen,  even  without  a  magnifier,  if  a 
radial  surface  of  split  wood  (not  smooth)  is  examined. 
The  entire  radial  face  will  be  seen  almost  covered, 
with  these  tiny  structures,  which  appear  as  fine  but 
conspicuous  cross-lines.  As  shown  in  Fig.  85,  the  cells 
of  the  medullary  or  pith  rays  are  smaller  and  very 
much  shorter  than  the  wood-fibres  or  tracheids,  see 
b,  Fig.  90,  and  their  long  axis  is  at  right  angles  to  that 
of  the  fibres.  In  pines  and  spruces  the  cells  of  the 
upper  and  lower  rows  of  each  tier  or  pith -ray  have 
"  bordered  "  pits  like  those  of  the  wood-fibres  or  tra- 
cheids proper,  but  the  cells  of  the  intermediate  rows, 
and  of  all  rows  in  the  rays  of  cedars,  etc.,  have  only 
"simple"  pits,  i.e.,  pits  devoid  of  the*  saucer-like 
"border"  or  rim. 

In  pine,  many  of  the  pith-rays  are  larger  than  the 


FIG.  87.— Block  of  Oak.  C.S.,  cross-section;  JR.8.,  radial 
section;  T.S.,  tangential  section  ;m. r. ,  medullary  or  pith  ray; 
a,  height,  b,  width,  mid  e,  length  of  a  pith- ray. 


212 


THE  MATERIALS  OF  CONSTRUCTION. 


majority,  each  containing  a  whitish  line,  the  horizontal  resin-duct,  which, 
though  much  smaller,  resembles  the  vertical  ducts  seen  on  the  cross-section. 
The  larger  vertical  resin-ducts  *  are  best  observed  on  the  removal  of  the  bark 
from  a  fresh  piece  of  white  pine,  cut  in  winter,  where  they  appear  as  con- 
spicuous white  linos,  extending  often  for  many  inches  up  and  down  the  stem. 
Neither  the  horizontal  nor  the  vertical  resin  ducts  are  vessels  or  cells, 
but  are  openings  between  cells,  i.e.,  intercellular  spaces  in  which  the  resin 
accumulates,  freely  oozing  out  when  the  ducts  of  a  fresh  piece  of  sap- 
wood  are  cut.  They  are  present  only  in  our  coniferous  woods,  and  even 
here  they  are  restricted  to  pine,  spruce,  and  larch,  and  are  normally  absent 
in  fir,  cedar,  cypress,  and  yew. 

Altogether  the  structure  of  coniferous  wood  is  very  simple  and  regular, 
the  bulk  being  made  up  of  smallfabres  called  tracheids,  the  disturbing  ele- 
ment, of  pith-rays  and  resin-ductsfceing  insignificant,  and  hence  the  great 
unifo/mity  and  great  technical  val^of  coniferous  wood.  - 

184.  Anatomical  Structurff"vP"Sjtad-leajed  Trees. — On  a  cross-section 

of  oak,  the  same  arrangement  of 
pith  and  bark,  of  sapwood  and 
heartwood,  and  the  same  disposi- 
tion of  the  wood  in  well-defined 
concentric  or  annual  rings  occurs, 
but  the  rings  are  marked  by  lines, 
or  rows,  of  conspicuous  pores  or 
openings  which  occupy  the 
greater  part  of  the  spring  wood 
of  each  ring  (see  Fig.  87,  also 
Fig.  89)  and  are,  in  fact,  the 
openings  through  the  vessels  cut 
by  the  section.  On  the  radial 
section,  or  quarter-sawed  board, 
the  several  layers  appear  as  so 
many  parallel  stripes  (see  Fig. 
88) ;  on  the  tangential  section  or 
"  bastard  "  face,  patterns  similar 
to  those  mentioned  for  pine  wood 
are  observed.  But  while  the  pat- 
terns in  hard  pine  are  marked  by 
the  darker  summer  wood  and  are 
FIG.  88.— Board  of  Oak.  CS,  cross-section;  ES,  composed  of  plain,  alternating 
radial  section;  TS,  tangential  section  ;i>,  vessels  stripes  of  darker  and  lighter 
or  pores,  cut  through;  A,  slighVcurve  in  log  WQod>  the  figures  jn  oak  (an(J 
which  appears  in  section  as  an  islet.  ofcher  broad.leaved  woods)  are 

due  chiefly  to  the  vessels,  those  of  the  spring  wood  in  oak  being  the  most 

*  See  rdt  Fig.  118. 


TIMBER. 


213 


conspicuous  (see  Fig.  88);  so  that  in  an  oak  table  the  darker,  shaded  parts 
are  the  spring  wood,  the  lighter  parts  the  summer  wood. 

On  closer  examination  of  the  smoothed  cross-section  of  oak,  the  spring- 
wood  part  of  the  ring  is  found  to  be  formed,  in  great  part,  of  pores:  large, 
round,  or  oval  openings  through  long  vessels.  These  are  separated  by  a 


FIG.  89.— Cross-section  of  Oak  magnified  about  5  times. 

grayish  and  quite  porous  tissue  (see  Fig.  89)  which  continues  here  and  there 
in  the  form  of  radial,  often  branched,  patches  (not  the  pith-rays)  into  and 
through  the  summer  wood  to  the  spring  wood  of  the  next  ring.  The  large 
vessels  of  the  spring  wood,  occupying  6  to  10  per  cent  of  the  volume  of  a 
log  in  very  good  oak,  and  25  per  cent  or  more  in  inferior  and  narrow-ringed 
lumber,  are  a  very  important  feature,  since 
it  is  evident  that  the  greater  their  share  in 
the  volume,  the  lighter  and  weaker  the 
wood.  They  are  smallest  near  the  pith,  and 
grow  wider  outward;  they  are  wider  in  the 
stem  than  limb  and  seem  to  be  of  indefinite 
length,  forming  open  channels  in  some  cases 
probably  as  long  as  the  tree  itself. 

Scattered  through  the  radiating  gray 
patches  of  porous  wood  are  vessels  similar  ' 
those  of  the  spring  wood,  but  decided^ 
smaller.  These  vessels  are  usually  fewer ^and 
larger  near  the  spring  wood,  and  smaller  and 
more  numerous  in  the  outer  portions  of  the  FIG.  90. —Portion  of  the  Firm  Bodies 
ring.  Their  number  and  sizecan  be  utilized  of  Fibres  with  Two  Cells  of  a  small 
to  distinguish  the  oaks  classed  as  white  oaks  Pilh-ray'  mr'  Highly  magnified. 
from  those  classed  as  black  and  red  oaks;  they  are  fewer  and  larger  in  red 
oaks,  smaller  but  much  more  numerous  in  white  oaks.  The  summer  wood, 
except  for  these  radial  grayish  patches,  is  daik-colored  and  firm.  This  firm 
portion,  divided  into  bodies  or  strands  by  these  patches  of  porous  wood  and 
also  by  fine  wavy  concentric  lines  of  short,  thin-walled  cells  (see  Fig.  89), 
consists  of  thick-walled  fibres  (see  Fig.  90)  and  is  the  chief  element  of 


214 


THE  MATERIALS  OF  CONSTRUCTION. 


strength  in  oak  wood.    In  good  white  oak  it  forms  one  half  and  more  of  the 
wood;  it  cuts  like  horn,  and  the  cut  surface  is  shiny  and  of  a  deep  chocolate- 
brown  color.     In  very  narrow-ringed  wood  and  in  inferior  red  oak  it 
is  usually  much  reduced  in  quantity  as  well  as  quality. 

The  pith-rays  of  the  oak,  unlike  those  of  coniferous  woods,  are  at 
least  in  part  very  large  and  conspicuous  (see  Fig.  87,  their  height  in- 
dicated by  the  letter  a,  and  their  width  by  the  letter  Z>).     The  large 
medullary  rays  of  oak  are  often  twenty  and  more  cells  thick  and  sev- 
eral hundred  cell-rows  in  height,  which  amount  commonly  to  one  or 
more  inches.     These  large   rays  are  con- 
spicuous on  all  sections.     They  appear  as 
long,  sharp,  grayish  lines  on  the  cross-sec- 
tion, as  short,  thick  lines,  tapering  at  each 
end,  on  the  tangential  or  "bastard  "  face, 
and   as    broad,    shiny    bands,   the  "silver 
grain  "  or  "  mirrors,"  on  the  radial  section. 
In  addition  to  these  coarse  rays,  there  is 
also  a  large  number   of   small   pith-rays, 
which  can  be  seen  only  when  magnified. 
On  the  whole,  the  pith-rays  form  a  much 
larger  part  of  the  wood  than  might  be  sup- 
posed.    In  specimens  of  good  white  oak  it 
has  been  found  that  they  formed  about  1C 
to  25  per  cent  of  the  wood. 

185.  Minute  Structure.  —  If  a  well- 
smoothed,  thin  disk  or  cross-section  of 
oak  (say  one-sixteenth  inch  thick)  is  held 
up  to  the  light,  it  looks  very  much  like  a 
sieve,  the  pores  or  vessels  appearing  as 
clean-cut  holes;  the  spring  wood  and  gray 
patches  are  seen  to  be  quite  porous,  but 
the  firm  bodies  of  fibres  between  them  are 
dense  and  opaque.  Examined  with  the 
magnifier  it  will  be  noticed  that  there  is 
no  such  regularity  of  arrangement  in 
straight  rows  as  is  conspicuous  in  the  pine; 
on  the  contrary,  great  irregularity  prevails. 
At  the  same  time,  while  the  pores  are  as 
as  large  as  pin-holes,  the  cells  of  the  denser 
wood,  unlike  those  of  pine  wood,  are  too 
small  to  be  distinguished.  Studied  with 
the  microscope,  each  vessel  is  found  to  be  a  vertical  row  of  a  great 
number  of  short,  wide  tubes,  joined  end  to  end  (Fig.  91,  6-).  The  porous 
spring  wood  and  radial  gray  tracts  are  partly  composed  of  smaller  vessels, 


FIG.  91.— Isolated  Fibres,  and  Cells. 

a,  four  cells  of  wood-parenchyma; 

b,  two  cells  from  a  pith-ray;  c,  a 
single  joint  or  cell  of  a  vessel,  the 
openings  x  leading  into  its  upper 
and  lower  neighbors;  d,  tracheid; 
e,  wood-fibre  proper. 


TIMBER. 


215 


but  chiefly  of  tracheids  like  those  of  pine,  and  of  shorter  cells,  the  "wood- 
parenchyma/'  resembling  the  cells  of  the  medullary  rays.  These  latter,  as 
well  as  the  fine  concentric  lines  mentioned  as  occurring  in  the  summer  wood, 
are  composed  entirely  of  short,  tube-like  parenchyma-cells  with  square  or 
oblique  ends  (Fig.  91,  a  and  b).  The  wood-fibres  proper,  which  form  the 
dark,  firm  bodies  referred  to,  are  very  fine,  thread-like  cells  one  twenty-fifth 
to  one-tenth  inch  long,  with  a  wall  commonly  so  thick  that  scarcely  any 
empty  internal  space  or  lumen  remains  (Figs.  91,  e,  and  90). 

If  instead  of  oak  a  piece  of  poplar  or  basswood  (Fig.  92)  had  been  used 
in  this  study,  the  structure  would  have  been  found  to  be  quite  different. 


FIG.  92 — Cross-section  of  Basswood  (magnified),     v,  vessels  ;  mr,  pith-rays. 

The  same  kinds  of  cell-elements,  vessels,  etc.,  are  present,  but  their  com- 
bination and  arrangement  is  different,  and  thus  from  the  great  variety  of 
possible  combinations  results  the  great  variety  of  structure  and,  in  conse- 
quence, of  the  qualities  which  distinguish  the  wood  of  broad-leaved  trees. 
The  sharp  distinction  of  sapwood  and  heartwood  is  wanting;  the  rings  are 
not  so  clearly  defined,  the  vessels  of  the  wood  are  small,  very  numerous, 
and  rather  evenly  scattered  through  the  wood  of  the  annual  ring,  so  that 
the  distinction  of  the  ring  almost  vanishes  and  the  medullary  or  pith  rays, 
in  poplar,  can  be  seen,  without  being  magnified,  only  on  the  radial  section. 

186.  Different  "Grains"  of  Wood.— The  terms  "fine-grained/'  "coarse- 
grained," "straight-grained,"  and  " cross-grained  "  are  frequently  applied 
in  woodworking.  In  common  usage,  wood  is  "  coarse-grained  "  if  its 
annual  rings  are  wide,  "  fine-grained  "  if  they  are  narrow;  in  the  finer  wood 
industries  a  "  fine-grained  "  wood  is  capable  of  high  polish,  while  a  "  coarse- 
grained "  wood  is  not,  so  that  in  this  latter  case  the  distinction  depends 
chiefly  on  hardness,  and  in  the  former  on  an  accidental  case  of  slow  or 
rapid  growth. 

Generally  the  direction  of  the  wood-fibres  is  parallel  to  the  axis  of  the 
stem  or  limb  in  which  they  occur,  the  wood  is  straight-grained,  but  in 
many  cases  the  course  of  the  fibres  is  spiral  or  twisted  around  the  tree  as 


THE  MATERIALS  OF  CONSTRUCTION 


shown  in  Fig.  93,  and  sometimes  (commonly  in  butts  of  gurn  and  cypress) 
the  fibres  of  several  layers  are  oblique  in  one  Direction,  and  those  of  the 


FIG.  93.  FIG.  94. 

FIG.  93. — Spiral  Grain.  Season-checks,  after  removal  of  bark,  indicate  the  direction  of 
the  fibres  or  grain. 

FIG.  94. — Alternating  Spiral  Grain  in  Cypress.  Side  and  end  view  of  same  piece.  When 
the  bark  was  at  o  the  grain  at  this  point  was  straight.  From  that  time  each  year  it 
grew  more  oblique  in  one  direction,  reaching  a  climax  at  a,  and  then  turned  back  in 
the  opposite  direction.  These  alternations  were  repeated  periodically,  the  bark 
sharing  in  these  changes. 

next  series  of  layers  are  oblique  in  the  opposite  direction,  as  shown. in 
Fig.  94;  the  wood  is  cross-  or  twisted-grained.  Wavy  grain  in  a  tan- 
gential plane  as  seen  on  the  radial  section  is  illustrated  in  Fig.  940,  which 

represents  an  extreme  case  observed  in  beech. 
This  same  form  also  occurs  on  the  radial  plane, 
causing  the  tangential  section  to  appear  wavy  or 
in  transverse  folds.  When  wavy  grain  is  fine, 
i.e.,  the  folds  or  ridges  small  but  numerous,  it 
gives  rise  to  the  "curly"  structure  frequently 
seen  in  maple.  Ordinarily,  neither  wavy,  spiral, 
nor  alternate  grain  is  visible  on  the  cross-section; 
its  existence  often  escapes  the  eye  even  on  smooth, 
longitudinal  faces  in  sawed  material,  so  that  the 

Tly  saf!  Sui1e  to  their  discovery  lies  in  splitting 

the  wood  m  the  two  normal  planes. 
Generally  the  surface  of  the  wood  under  the  bark,  and  therefore  also 
that  of  any  layer  in  the  interior,  is  not  uniform  and  smooth,  but  is  chan- 
nelled and  pitted  by  numerous  depressions  which  differ  greatly  in  size  and 
form.  Usually,  any  one  depression  or  elevation  is  restricted  to  one  or  a 
few  annual  layers  (i.e.,  seen  only  in  one  or  a  few  rings),  and  is  then  lost, 


TIMBER. 


217 


being  compensated  (the  surface  at  the  particular  spot  evened  up)  by  growth. 

In  some  woods,  however,'wny  depression  or  elevation  once  attained  grows 

from  year  to  year  and  reaches  a  maximum  size  which  is  maintained  for 

many  years,  sometimes  throughout  life. 

In  maple,  where  this  tendency   to  preserve  any  particular  contour  is 

very  great,  the  depressions  and  elevations  are  usually  small  (commonly  less 

than   one-eighth   inch,  but  very  numerous.     On 

tangent  boards  of  such  wood  the  sections  of  these 

pits  and  prominences  appear  as  circlets  and  give 

rise    to   the    beautiful.  "  bird Veye  "    or   "land- 
scape "  structure.     Similar  structures  in  the  burls 

of  black  ash,  maple,  etc.,  are  frequently  due  to 

the  presence  of  dormant  buds,  which  cause  the 

surface  of  all  the  layers  through  which  they  pass 

to  be  covered  by  small  conical  elevations,  whose 

cross-sections  on  the  sawed  board  appear   as  ir- 
regular circlets  or  islets  each  with  a  dark  speck, 

the  section  of  the  pith  or  "  trace  "  of  the  dor- 
mant bud  in  the  centre. 

In  the  wood  of  many  broad-leaved  trees  the 
wood-fibres  are  much  longer  when  full  grown 
than  when  they  are  first  formed  in  the  cambium 
or  growing  zone.  This  causes  the  tips  of  each 
fibre  to  crowd  in  between  the  fibres  above  and 
below,  and  leads  to  an  irregular  interlacement  of 
these  fibres,  which  adds  to  the  toughness  but 
reduces  the  cleavability  of  the  wood. 

At  the  junction  of  limb  and  stem  the  fibres 
on  the  upper  and  lower  sides  of  the  limb  behave 
differently.  On  the  lower  side  they  run  from  the 
stem  into  the  limb,  forming  an  uninterrupted 
strand  or  tissue  and  a  perfect  union.  On  the 
upper  side  the  fibres  bend  aside,  are  not  con- 
tinuous into  the  limb,  and  hence  the  connection 
is  imperfect  (Fig.  95). 

Owing  to  this  arrangement  of  the  fibres,  the 
cleft  made  in  splitting  never  runs  into  the  knot, 
if  started  on  the  side  above  the  limb,  but  is  apt 
to  enter  the  knot  if  started  below,  a  fact  well 
understood  in  woodcraft.  When  limbs  die,  de- 
cay, and  break  off,  the  remaining  stubs  are  sur- 
rounded and  may  finally  be  covered  by  the  growth 
of  the  trunk,  and  thus  give  rise  to  the  annoying  " 


55. —Section  of  Wood 
showing  Position  of  the 
Grain  at  Base  of  a  Limb 
which  has  been  Dead  Three 
Years.  P,  pith  of  both 
stem  and  limb  ;  1-7,  seven 
yearly  layers  of  wood;  a, 
b,  knot  or  basal  part  of  a 
limb  which  lived  four 
years,  then  died  and  broke 
off  near  the  stem,  leaving 
the  part  to  the  left  of  a,  b, 
a  "  sound  "  knot,  the  part 
to  the  right  a  "  dead  " 
knot,  which  would  soon  be 
entirely  covered  by  the 
growing  stem. 


dead  "  or  "  loose  "  knots. 
187.  Color  and  Odor. — Color,  like   structure,  lends  beauty  to  the  wood, 


218  THE  MATERIALS  OF  CONSTRUCTION. 

aids  in  its  identification,  and  is  of  great  value  in  ^.he  determination  of  its 
quality.  Considering  only  the  heartwood,  the  black  color  of  the  per- 
simmon, the  dark  brown  of  the  walnut,  the  light  brown  of  the  white  oaks, 
the  reddish  brown  of  the  red  oaks,  the  yellowish  white  of  the  tulip  and 
poplar,  the  brownish  red  of  the  redwood  and  cedar,  the  yellow  of  the  papaw 
and  sumac,  are  all  reliable  marks  of  distinction;  and  color  together  with 
lustre  and  weight  are  only  too  often  the  only  features  depended  upon  in 
practice.  Newly  formed  wood,  like  that  of  the  outer  few  rings,  has  but 
little  color.  The  sapwood  generally  is  light,  and  the  wood  of  trees  which 
form  no  heartwood  changes  but  little,  except  when  stained  by  forerunners 
of  disease. 

The  different  tints  of  colors,  whether  the  brown  of  oak,  the  orange- 
brown  of  pine,  the  blackish  tint  of  walnut,  or  the  reddish  cast  of  cedar,  are 
due  to  pigments,  while  the  deeper  shade  of  the  summer-wood  bands  in  pine 
and  cedar,  or  in  oak  or  walnut,  is  due  to  the  fact  that,  the  wood  being 
denser,  more  of  the  colored  wood  substance  occurs  on  a  given  space,  i.e., 
there  is  more  colored  matter  per  square  inch. 

Wood  is  translucent,  a  thin  disk  of  pine  permitting  light  to  pass 
through  quite  freely.  This  translucency  affects  the  lustre  and  brightness 
of  lumber.  When  wood  is  attacked  by  fungi  it  becomes  more  opaque,  loses 
its  brightness,  and  in  practice  is  designated  "dead"  in  distinction  from 
"live  "or  bright  timber.  Exposure  to  air  darkens  all  wood;  direct  sun- 
light and  occasional  moistening  hasten  this  change  and  cause  it  to  pene- 
trate deeper.  Prolonged  immersion  has  the  same  effect,  pine  wood  becom- 
ing a  dark  gray,  while  oak  changes  to  a  blackish  brown. 

Odor,  like  color,  depends  on  chemical  compounds,  forming  no  part  of 
the  wood  substance  itself.  Exposure  to  weather  reduces  and  often 
changes  the  odor,  but  a  piece  of  dry  long-leaf  pine,  cedar,  or  camphor  wood 
exhales  apparently  as  much  odor  as  ever  when  a  new  surface  is  exposed.. 

Heartwood  is  more  odoriferous  than  sapwood.  Many  kinds  of  wood  are 
distinguished  by  strong  and  peculiar  odors.  This  is  especially  the  case 
with  camphor,  cedar,  pine,  oak,  and  mahogany,  and  the  list  would  com- 
prise every  kind  of  wood  in  use  were  our  sense  of  smell  developed  in  keep- 
ing with  its  importance.  Decomposition  is  usually  accompanied  by  pro- 
nounced odors;  decaying  poplar  emits  a  disagreeable  odor,  while  red  oak 
often  becomes  fragrant,  its  smell  resembling  that  of  heliotrope. 

188.  Resonance. — If  a  log  or  scantling  is  struck  with  the  axe  or  hammer, 
a  sound  is  emitted  which  varies  in  pitch  and  character  with  the  shape  and 
size  of  the  stick,  and  also  with  the  kind  and  condition  of  wood.  Not  only 
can  sound  be  produced  by  a  direct  blow,  but  a  thin  board  may  be  set  vibrat- 
ing and  be  made  to  give  a  tone  by  merely  producing  a  suitable  tone  in  its 
vicinity.  The  vibrations  of  the  air,  caused  by  the  motion  of  the  strings  of 
the  piano,  communicate  themselves  to  the  board,  which  vibrates  in. the 
same  intervals  as  the  string  and  reenforces  the  note.  The  note  which  a 


TIMBER.  219 

given  piece  of  wood  may  emit  varies  in  pitch  directly  with  the  elasticity, 
and  indirectly  with  the  weight,  of  the  wood.  The  ability  of  a  properly 
shaped  sounding-board  to  respond  freely  to  all  the  notes  within  the  range 
of  an  instrument,  as  well  as  to  reflect  the  character  of  the  notes  thus 
emitted  (i.e.,  whether  melodious  or  not),  depends,  first,  on  the  structure  of 
the  wood  and  next  on  the  uniformity  of  the  same  throughout  the  board. 
In  the  manufacture  of  musical  instruments  all  wood  containing  defects, 
knots,  cross  grain,  resinous  tracts,  alternations  of  wide  and  narrow  rings, 
and  all  wood  in  which  summer  and  spring  wood  are  strongly  contrasted  in 
structure  and  variable  in  their  proportions,  is  rejected,  and  only  radial 
sections  (quarter-sawed 'or  split)  of  wood  of  uniform  structure  and  growth 
are  used. 

The  irregularity  in  structure,  due  to  the  presence  of  relatively  large 
pores  and  pith-rays,  excludes  almost  all  our  broad-leaved  woods  from  such 
use,  while  the  number  of  eligible  woods  among  conifers  is  limited  by  the  ne- 
cessity of  combining  sufficient  strength  with  uniformity  in  structure,  absence 
of  two  pronounced  bands  of  summer  wood,  and  relative  freedom  from  resin. 

Spruce  is  the  favored  resonance  wood;  it  is  used  for  sounding-boards 
both  in  pianos  and  violins,  while  for  the  resistant  back  and  sides  of  the  latter 
the  highly  elastic  hard  maple  is  used.  Preferably  resonance  wood  is  not 
bent  to  assume  the  final  form;  the  belly  of  the  violin  is  shaped  from  a 
thicker  piece,  so  that  every  fibre  is  as  nearly  in  its  original  unstrained  con- 
dition as  possible,  and  therefore  free  to  vibrate.  All  wood  for  musical 
instruments  is,  of  course,  well  seasoned,  the  final  drying  in  kiln  or  warm 
room  being  preceded  by  careful  seasoning  at  ordinary  temperatures  often 
for  as  many  as  seven  years  or  more.  The  improvement  of  violins,  not  by 
age  but  by  long  usage,  is  probably  due  not  only  to  the  adjustment  of  the 
numerous  component  parts  to  each  other,  but  also  to  a  change  in  the  wood 
itself;  years  of  vibrating  enabling  any  given  part  to  vibrate  much  more 
readily.  \ 

"*»      SPECIFIC   GRAVITY,    OR   WEIGHT. 

189.  Weight  Dependent  on  Structure   and  Moisture. — A   small   cross- 
section  of  wood,  as  in  Fig.  96,  dropped  into  water,  sinks,  showing  that  the 
substance  of  which  wood-fibre  or  wood  is  built  up  is  heavier 
than  water.     By  immersing  the  wood  successively  in  heavier 
liquids,  until  we  find  a  liquid  in  which  it  does  not  sink, 
and  comparing  the  weight  of  the  same  with  water,  we  find 
that  wood-substance  is  about  1.6  times  as  heavy  as  water, 

and  that  this  is  as  true  of  poplar  as  of  oak  or  pine. 

c,  , .  ,  •      T-T      ™          -i      •  Cross  -  section 

Separating  a  single  cell,  as  shown  in  Fig.  97,  a,  drying      of  ^  Grou  D  of 

and   then   dropping   it   into  water,  it  floats.     The  air-filled      Wood  fibres, 
cell-cavity  or  interior  reduces  its  weight,  and,  like  a  corked 
empty  bottle,  it  weighs  less  than  the  water.     Soon,  however,  -water  soaks 
into  the  cell,  when  it  fills  up  and  sinks. 


220  THE  MATERIALS  OF  CONSTRUCTION. 

Many  such  cells  grown  together,  as  in  a  block  of  wood,  sink  when  all  or 
most  of  them  are  filled  with  water,  but  will  float  as  long  as  the  majority  are 
empty  or  only  partly  filled.  This  is  why  a  green,  sappy  pine  pole  soon 
sinks  in  "  driving  "  (floating).  Its  cells  are  largely  filled  before  it  is  thrown 
in,  and  but  little  additional  water  suffices  to  make  its  weight  greater  than 
that  of  the  water. 

In  a  white-pine  log,  composed  chiefly  of  empty  cells  (heart wood),  the 
water  requires  a  very  long  time  to  fill  up  the  cells  (five  years  would  not 
suffice  to  fill  them  all),  and  therefore  the  log  may  float  for  many  months  or 
even  years.  When  the  wall  of  the  wood-fibre  is  very  thick  (five-eighths  or 
more  of  the  volume),  as  in  Fig.  97, 1,  the  fibre  sinks  whether  empty  or  filled. 
This  applies  to  most  of  the  fibres  of  the  dark  summer-wood 
bands  in  pines,  and  to  the  compact  fibres  of  oak  or  hickory, 
and  many,  especially  tropical  woods,  have,  such  thick- walled 
.cells  and  so  little  empty  or  air  space  that  they  never  float. 

Here,  then,  are  the  two  main  factors  of  weight  in  wood: 
The  amount  of  cell-wall,  or  wood-substance,  constant  for  any 
given  piece,  and  the  amount  of  water  contained  in  the  wood, 
variable  even  in  the  standing  tree,  and  only  in  part  eliminated 
in  drying. 

The  weight  of  the  green  wood  of  any  species  varies  chiefly 
as  the  second  factor,  and  is  entirely  misleading  if  the  relative 
weight  of  different  kinds  is  sought.  Thus  some  green  sticks 
of  the  otherwise  lighter  cypress  and  gum  sink  more  readily 
than  fresh  oak. 

*  The  weight  of  sapwood,  or  the  sappy  peripheral  part  of 

our  common  lumber  woods,  is  always  great  whether  cut  in 
winter  or  summer.     It  rarely  falls  much  below  45  pounds  and' 
commonly  exceeds  55  pounds  to  the  cubic  foot,  even  in  our  lighter  wooded 
species. 

It  follows  that  the  green  wood  of  a  sapling  is  heavier  than  that  of  an 
old  tree,  the  fresh  wood  from  a  disk  of  the  upper  part  of  a  tree  often 
heavier  than  that  of  the  lower  part,  and  the  wood  near  the  bark  heavier 
than  that  nearer  the  pith,  and  also  that  the  advantage  of  drying  the  wood 
before  shipping  is  most  important  in  sappy  and  light  kinds. 

When  kiln-dried,  the  misleading  moisture  factor  of  weight  is  uniformly 
reduced  and  a  fair  comparison  made  possible.  For  the  sake  of  convenience 
in  comparison,  the  weight  of  wood  is  expressed  either  as  the  weight  per  cubic 
foot  or,  what  is  still  more  convenient,  as  specific  weight  or  density. 

190.  Variation  in  Weight  in  a  Single  Trunk. — If  an  old  long-leaf  pine 
is  cut  up  as  shown  in  Fig.  98,  the  wood  of  disk  No.  1  is  heavier  than  that 
of  disk  No.  2,  the  latter  heavier  than  that  of  disk  No.  3,  and  the  wood  of 
the  top  disk  is  found  to  be  only  about  three  fourths  as  heavy  as  that  of 
disk  No.  1. 


TIMBER.  221 

Similarly,  if  disk  No.  2  is  cut  up  as  in  the  figure,  the  specific  weight  of 
the  different  pieces  is: 

a  about  0.52 

I  about  0.64 

c  about  0.67 

d,  e,f  about  0.65 

Showing  that  in  this  disk,  at  least,  the  wood  formed  during  the  many  years' 
growth,  represented  in  piece  a,  is  much  lighter  than  that  of  former  years. 
It  also  shows  that  the  best  wood  is  the  middle  part,  with  its  large  proportion 
of  dark  summer-wood  bands. 

Cutting  up  all  disks  in  the  same  way,  it  will  be  found  that  the  piece  a 
of  the  first  disk  is  heavier  than  piece  a  of  the  fifth,  and  that  piece  c  of  the 
first  disk  excels  the  piece  c  of  all  the  other  disks.  This  shows  that  the  wood 
grown  during  the  same  number  of  years  is  lighter  in  the  upper  parts  of  the 
stem;  and  if  the  disks  are  smoothed  on  their  radial  surfaces  and  set  up  one 
on  top  of  the  other  in  their  regular  order  for  sake  of  comparison,  this  decrease 
in  weight  will  be  seen  to  be  accompanied  by  a 
decrease  in  the  amount  of  summer  wood.  The 
color  effect  of  the  upper  disks  is  conspicuously 
lighter. 

If  our  old  pine  had  been  cut  one  hundred 
and  fifty  years  ago,  before  the  outer,  lighter  wood 
was  laid  on,  it  is  evident  that  the  weight  of  the  wood 
of  any  one  disk  would  have  been  found  to  increase 
from  the  centre  outward,  and  no  subsequent  decrease 
could  have  been  observed. 

In  a  thrifty  young  pine,  then,  the  wood  is  heav-  FlG"    98-~ 
ier  from  the  centre  outward,  and  lighter  from  below 

upward;  only  the  wood  laid  on  in  old  age  fails  in  weight  below  the 
average.  The  number  of  brownish  bauds  of  summer  wood  are  a  direct  indi- 
cation of  these  differences. 

If  an  old  oak  is  cut  up  in  the  same  manner,  the  butt  cut  is  also  found 
heaviest  and  the  top  lightest,  but,  unlike  the  disk  of  pine,  the  disk  of  oak  has 
its  firmest  wood  at  the  centre,  and  each  successive  piece  from  the  centre  out- 
ward is  lighter  than  its  inner  neighbor. 

Examining  the  pieces,  this  difference  is  not  as  readily  explained  by  the 
appearance  of  each  piece  as  in  the  case  of  pine  wood.  Nevertheless,  one  con- 
spicuous point  appears  at  once:  the  pores,  so  very  distinct  in  oak,  are  very 
minute  in  the  wood  near  the  centre  and  thus  the  wood  is  far  less  porous. 
Studying  different  trees  it  is  found  that,  in  the  pines,  wood  with  narrow 
rings  is  just  as  heavy  as,  and  often  heavier  than,  the  wood  with  wider  rings, 
but  if  the  rings  are  unusually  narrow  in  any  part  of  the  disk  the  wood  has 
a  lighter  color;  that  is,  there  is  less  summer  wood  and  therefore  less  weight. 

In  oak,  ash,  or  elm  trees  of  thrifty  growth,  the  wider  rings  (not  less  than 


222 


THE  MATERIALS   OF  CONSTRUCTION. 


one-twelfth  inch)  always  form  the  heaviest  wood,  while  any  piece  with  very 
narrow  rings  is  light.  On  the  other  hand/the  weight  of  a  piece  of  hard 
maple  or  birch  is  quite  independent  of  the  width  of  its  rings,  since  the 
structure  here  is  uniform  across  the  entire  width  of  the  annual  ring. 

The  bases  of  limbs  (knots)  are  usually  heavy,  very  heavy  in  conifers,  and 
also  the  wood  which  surrounds  them,  but  generally  the  wood  of  the  limbs  is 
lighter  than  that  of  the  stem,  and  the  wood  of  the  roots  is  the  lightest. 

191.  Weight  of  Different  Species.— In  general,  it  may  "be  said  that  none 
of  the  native  woods  in  common  use  in  this  country  are,  when  dry,  as  heavy 
as  water,  i.e.,  G2  pounds  to  the  cubic  foot.  Few  exceed  50  pounds,  while 
most  of  them  fall  below  40  pounds,  and  much  of  the  pine  and  other  conif- 
erous wood  weighs  less  than  30  pounds  per  cubic  foot. 

The  weight  of  the  wood  is,  in  itself,  an  important  quality.  Weight  assists 
in  distinguishing  maple  from  poplar.  Lightness,  coupled  with  great  strength 
and  stiffness,  recommends  wood  for  a  thousand  different  uses.  To  a  large 
extent  weight  predicates  the  strength  of  the  woody  at  least  in  the  same  species, 
so  that  a  heavy  piece  of  oak  will  exceed  in  strength  a  light  piece  of  the  same 
species,  and  in  pine  it  appears  probable  that,  weight  for  weight,  the  strength 
of  the  wood  of  various  pines  is  nearly  equal,  all  being  reduced  to  the  same 

*ee  of  dry  ness. 


WEIGHT    OF    KILN-DKIED   WOOD    OF   DIFFERENT   SPECIES. 


Common  Name  of  Species. 

Approximate. 

Specific 
Gravity. 

Weight  of- 

1  cubic 
foot. 

1000  feet 
of  lum- 
ber. 

(a)  Very  heavy  woods: 
*  Hickory,  oak,  persimmon,  osage  orange,  black  locust, 
hackberry    blue  beecb   best  of  elm   and  ash  

0.70-0.80 
.60-  .70 
.50-  .60 

.40-  .50 
.30-   .40 

Pounds. 

42-48 
36-42 
30-36 

24-30 

18-24 

Pounds. 
3700 

3200 
2700 

2200 
1800 

(b)  Heavy  woods: 
Ash,  elm,  cherry,  birch,  maple,  beech,  walnut,  sour  gum, 
coffee-tree,  honey-locust,  best  of    Southern  pine,  and 
tamarack                                       

(c)  "Woods  of  medium  weight: 
Southern  pine,  pitch-pine,   tamarack,   Douglas    spruce, 
Western  hemlock,  sweet  gum,  soft  maple,  sycamore, 
sassafras,  mulberry,  light  grades  of  birch  and  cherry.  . 
(d)  Light  woods: 
Norway  and  bull  pine,  red  cedar,  cypress,  hemlock,  the 
heavier  spruce  and  fir,   redwood,   basswood,  chestnut, 
butternut,  tulip,  catalpa,  buckeye,  heavier  grades  of  poplar 
(e)  Very  light  woods  : 

*  For  the  scientific  names  of  timbers  see  the  list  of  Useful  American  Timbers  at  the 
end  of  this  chapter. 


TIMBER.  223 

Since  ordinary  lumber  contains  knots  and  also  more  water  than  is  here 
assumed,  and  also  since  its  dimensions  either  exceed  or  fall  short  of  perfect 
measurement,  the  figures  in  the  table  are  only  approximate. 
Thus  1000  feet,  13.  M.,  of  long-leaf  pine  weighs: 

Pounds. 

Rough  and  green 4500 

Boards  rough  but  seasoned 3500 

Boards  dressed  and  seasoned 3000 

Flooring,  matched  dressed  and  seasoned 2500 

Weather-boarding,  bevelled  and  dressed. 1500 

MOISTURE  IN  WOOD. 

192.  Moisture  Distribution. — Water  may  occur  in  wood  in  three  con- 
ditions: (1)  it  forms  the  greater  part  (over  90  per  cent)  of  the  proto- 
plasmic contents  of  the  living  cells;  (2)  it  saturates  the  walls  of  all 
cells;  and  (3)  it  entirely  or  at  least  partly  fills  the  cavities  of  the  life- 
less cells,  fibres,  and  vessels.  In  the  sapwood  of  pine  it  occurs  in  all 
three  forms;  in  the  heartwood  only  in  the  second  form,  that  is,  it 
merely  saturates  the  walls.  Of  100  pounds  of  water  associated  with 
100  pounds  of  dry  wood-substance  in  200  pounds  of  fresh  sapwood  of 
white  pine,  about  35  pounds  are  needed  to  saturate  the  cell  walls, 
less  than  5  pounds  are  contained  in  living  cells,  and  the  remaining  60 
pounds  partly  fill  the  cavities  of  the  wood-fibres.  This  latter  forms  the 
sap  as  ordinarily  understood.  It  is  water  brought  from  the  soil,  containing 
small  quantities  of  mineral  salts,  and  in  certain  species  (maple,  birch,  etc.) 
it  also  contains  at  certain  times  a  small  percentage  of  sugar  and  other 
organic  matter.  These  organic  substances  are  the  dissolved  reserve  food 
stored  during  winter  in  the  pith-rays,  etc.,  of  the  wood  and  bark;  generally 
but  a  mere  trace  of  them  is  to  be  found.  From  this  it  appears  that  the 
solids  contained  in  the  sap,  such  as  albumen,  gum,  sugar,  etc.,  cannot 
exercise  the  influence  on  the  strength  of  the  wood  which  is  so  commonl^ 
claimed  for  them. 

The  Avood  next  to  the  bark  contains  "the  most  water.  In  the  species 
which  do  not  form  heartwood  the  decrease  toward  the  pith  is  gradual;  but 
where  this  is  formed,  the  change  from  a  more  moist  to  a  drier  condition  is 
usually  quite  abrupt  at  the  sapwood  limit.  In  long-leaf  pine  the  wood  of 
the  outer  1  inch  of  a  disk  may  contain  50  per  cent  of  water,  that  of  the 
next,  or  second  inch,  only  35  per  cent,  and  that  of  the  heartwood  only  20 
per  cent.  In  such  a  tree  the  amount  of  water  in  an  entire  cross-section 
varies  with  the  amount  of  sapwood,  and  is  therefore  greater  for  the  upper 
than  the  lower  cuts,  greater  for  limbs  than  stems,  and  greatest  of  all  in  the 
roots. 

Different  trees,  even  of  the  same  kind  and  from  the  same  place,  differ 
as  to  the  amount  of  water  they  contain.  A  thrifty  tree  contains  more  water 


224  THE  MATERIALS  OF  CONSTRUCTION. 

than  a  stunted  one,  and  a  young  tree  more  than  an  old  one,  while  the  wood 
of  all  trees  varies  in  its  moisture  relations  with  the  season  of  the  year. 

Contrary  to  the  general  belief,  a  tree  contains  about  as  much  water  in 
winter  as  in  summer.  The  fact  that  the  bark  peels  easily  in  the  spring 
depends  on  the  presence  of  incomplete,  soft  tissue,  the  rapidly  growing 
cambium  layer  found  between  wood  and  bark  during  this  season,  and  has 
little  to  do  with  the  total  amount  of  water  contained  in  the  wood,  of  the 
stem. 

Even  in  the  living  tree  a  flow  of  sap  from  a  cut  occurs  only  in  certain 
kinds  of  trees  and  under  special  circumstances;  from  boards,  timber,  etc., 
the  water  does  not  flow  out,  as  is  sometimes  believed,  but  must  be  evapo- 
rated.* 

193.  Drying  Timber. — The  rapidity  with  which  water  is  evaporated, 
that  is,  the  rate  of  drying,  depends  on  the  size  and  shape  of  the  piece  and 
on  the  structure  of  the  wood.  An  inch  board  dries  more  than  four  times 
as  fast  as  a  4-inch  plank  and  more  than  twenty  times  as  fast  as  a  10-inch 
timber.  White  pine  dries  faster  than  oak.  A  very  moist  piece  of  pine  or 
oak  will,  during  one  hour,  lose  more  than  four  times  as  much  water  per 
square  inch  from  the  cross-section,  but  only  one  half  as  much  from  the 
tangential  as  from  the  radial  section. 

In  a  long  timber,  where  the  end  or  cross-sections  form  but  a  small  part 
of  the  drying  surface,  this  difference  is  not  so  evident.  Nevertheless,  the 
ends  dry  and  shrink  first,  and  being  opposed  in  this  shrinking  by  the  more 
moist  adjoining  parts  they  check,  the  cracks  largely  disappearing  as  season- 
ing progresses. 

High  temperatures  are  very  effective  in  evaporating  the  water  from 
wood  no  matter  how  humid  the  air.  A  fresh  piece  of  sap  wood  may  lose 
weight  in  boiling  water,  and  can  be  dried  to  quite  an  extent  in  hot  steam. 

Kept  on  a  shelf  in  an  ordinary  dwelling,  wood  still  retains  8  to  10  per 
cent  of  its  weight  of  water,  and  this  percentage  is  always  greater  than  the 
percentage  of  moisture  in  the  surrounding  air.  Nor  is  the  amount  of 
water  in  dry  wood  constant;  the  weight  of  a  panful  of  shavings  varies; 
with  the  time  of  day,  being  on  a  summer  day  greatest  in  the  morning  and 
least  in  the  afternoon. 

Desiccating  the  air  with  chemicals  will  cause  the  wood  to  dry,  but  wood 
thus  dried  at  80°  R  will  still  lose  water  in  the  kiln.  Wood  dried  at  120° 
F.  loses  water  still  if  dried  at  200°  F.,  and  this  again  will  lose  more  water 
if  the  temperature  is  raised.  Absolutely  dry  wood  cannot  be  obtained; 
chemical  destruction  sets  in  before  all  the  water  is  driven  off. 

On  removal  from  the  kiln  the  wood  at  once  takes  up  water  from  the  air,  j 

*The  seeming  exceptions  to  this  rule  are  mostly  referable  to  two  causes,  namely.'; 
(a)  Clefts  or  "shakes"  will  allow  water  contained  in  them,  to  flow  out.  (b)  Froroj 
sound  wood,  if  very  sappy,  water  is  forced  out  whenever  the  wood  is  warmed,  just  as  ; 
water  flows  from  green  wood  in  the  stove. 


TIMBER.  225 

even  in  the  driest  weather.  At  first  the  absorption  is  quite  rapid;  at  the 
end  of  a  week  a  short  piece  of  pine,  1£  inches  thick,  has  regained  two 
thirds  of,  and  in  a  few  months  all,  the  moisture  which  it  had  when  air-dry, 
8  to  10  per  cent,  and  also  its  former  dimensions. 

In  thin  boards  all  parts  soon  attain  the  same  degree  of  dryness;  in 
heavy  timbers  the  interior  remains  moister  for  many  months,  and  even 
years,  than  the  exterior  parts.  Finally  an  equilibrium  is  reached,  and  then 
only  the  outer  parts  change  with  the  weather. 

With  kiln-dried  wood  all  parts  are  equally  dry,  and  when  exposed  the 
moisture  coming  from  the  air  must  pass  in  through  the  outer  parts,  and 
thus  the  order  is  reversed.  Timber  seasoned  out  of  doors  requires  months, 
or  even  years,  before  it  is  at  its  best;  kiln-dry  timber,  if  properly  handled, 
is  prime  at  once. 

Dry  wood  when  soaked  in  water  soon  regains  its  original  volume,  and 
in  the  heartwood  portion  it  may  even  surpass  it;  that  is  to  say,  swell  to  a 
larger  dimension  than  it  had  when  green.  With  the  soaking  it  continues 
to  increase  in  weight,  the  cell-cavities  filling  with  water,  and  if  left  many 
months  all  pieces  sink.  Yet  even  after  a  year's  immersion  a  piece  of  oak 
2  by  2  inches  and  only  6  inches  long  still  contains  air,  i.e.,  it  has  not 
taken  up  all  the  water  it  can.  By  rafting,  or  prolonged  immersion,  wood 
loses  some  of  its  weight,  soluble  materials  being  leached  out,  but  it  is  not 
impaired  either  as  fuel  or  as  building  material.  Immersion  and,  still  more, 
boiling  and  steaming  reduce  the  hygroscopicity  of  wood  and,  therefore,  also 
the  troublesome  "  working,"  or  shrinking  and  swelling. 

Exposure  in  dry  air  to  a  temperature  of  300°  F.  for  a  short  time  re- 
duces, but  does  not  destroy,  the  hygroscopicity  and  with  it  the  tendency  to 
shrink  and  swell.  A  piece  of  red  oak  which  has  been  subjected  to  a  tem- 
perature of  over  300°  F.  still  swells  in  hot  water  and  shrinks  in  the  kiln. 

In  artificial  drying,  temperatures  of  from  158°  to  180°  F.  are  usually 
employed.  Pine,  spruce,  cypress,  cedar,  etc.,  are  clried  fresh  from  the  saw, 
allowing  four  days  for  1-inch  boards;  hard  woods,  especially  oak,  ash, 
maple,  birch,  sycamore,  etc.,  are  air-seasoned  for  three  to  six  months,  to 
allow  the  first  shrinkage  to  take  place  more  gradually,  and  are  then  exposed 
to  the  above  temperatures  in  the  kiln  for  about  six  to  ten  days  for  1-inch 
lumber.  Freshly  cut  poplar  and  cotton  wood  are  often  dried  directly  in 
kilns. 

By  employing  lower  temperatures,  100°  to  120°  F.,  green  oak,  ash,  etc., 
can  be  seasoned  in  dry  kilns  without  danger  to  the  material.*  Steaming 
the  lumber  is  commonly  resorted  to  in  order  to  prevent  checking  and 
"  casehardening,"  but  not,  as  has  frequently  been  asserted,  to  enable  the 
board  to  dry.  Yard-dried  lumber  is  not  dry,  and  its  moisture  is  too  un- 

*  The  dry  kiln  shown  in  Fig.  99  is  operated  at  this  temperature,  and  -live  steam  is 
admitted  once  or  twice  a  day  to  prevent  checking. — J.  B.  J. 


226 


THE  MATERIALS  OF  CONSTRUCTION. 


evenly  distributed   to  insure   good  behavior  after  manufacture.     Careful 
piling  of  the  lumber  both  in  the  yard  and  kiln,  is  essential  to  good  drying. 


•  nnnnnnnnnnci^ 


: 


©  ©  ©  ©  © 
©  ©  ©  ©  ©© 
©©©©©© 
©©©©©© 
o  o  o  ©  o  o 
©©©©©©' 
©©©©©© 
©©©©©© 
©  ©  ©  ©, 


f  Steam 
Coils 


Lumber  Dryer  for  U.S.  Test  Timbers 

Dimensions:  —  Length  —  3O  ft. 

Heigth    —  16  ft. 

Width    —  12.  ft. 
FIG.  99. 

Piling  boards  on  edge  or  standing  them  on  end  is  believed  to  hasten  drying. 
This  is  true  only  because  in  either  case  the  air  can  circulate  more  freely 
.around  them  than  when  they  are  piled  in  the  ordinary  way.  Boards  on 


TIMBER. 


227 


end  dry  unequally;   the  upper  half  dries  much  faster  than  the  lower  half 
and  horizontal  piling  is,  therefore,  preferable. 

Since  the  proportion  of  sap-  and  heart- wood  varies  with  size,  age,  species, 
and  individual,  the  following  figures  must  be  regarded  as  mere  approxima- 
tions : 

POUNDS   OF   WATER  LOST   IX    DRYING    100    POUNDS   OF    GREEN   WOOD 

IN   THE   KILN. 


Common  Names  of  Species. 

Sap  wood  or 
Outer  Part. 

Heartwood 
or  Interior. 

45-65 

16-25 

(2)  Cypress,  extremely  variable     

50-65 

18-60 

(3)  Poplar,  cot  ton  wood    basswood  

60-65 

40-60 

(4)  Oak,  beech,  ash,  elm,  maple,   birch,  hickory,  chestnut,  wal- 
nut, and  sycamore  ... 

40-50 

30-40 

The  lighter  kinds  have  the  most  water  in  the  sapwood;  thus  sycamore  has  more  than 

hickory. 

SHRINKAGE  OF  WOOD. 

194.  Shrinkage  Explained. — When  a  short  piece  of  wood-fibre,  such  as 
that  shown  in  Fig.  100,  A,  is  dried  it  shrinks,  its  wall  grows  thinner  (as  in- 
dicated by  dotted  lines),  its  width,  ab, 
the  thickness  of  the  fibre,  becomes 
smaller,  and  the  cavity  or  opening 
larger,  but,  strange  to  say,  the  height 
or  length,  lc,  remains  the  same.  In  a 
similar  piece  of  fibre  with  a  thinner 
wall  (Fig.  100,  B)  the  effect  is  the 
same,  but  the  wall  being  only  half  as 
thick  the  total  change  is  only  about 
half  as  great.* 

If  sections  or  pieces  of  fibres  are 
dried  and  then  placed  on  moist  blotting- 
paper,  they  will  take  up  water  and 
swell  to  their  original  size,  though  the 
water  has  been  taken  up  only  by  their 
walls  and  none  has  entered  into  their 
lumina. 


openings    or 


This    indicates   FIG.  100.— Short  Pieces  of  Wood-fibres, 


one  thick-,  the  other  thin-walled;  mag- 
nified. 


that  the  water  in  the  cavity  or  lumen  of 
a  fibre  has  nothing  to  do  with  its  di- 
mensions, and  that  if  the  cell-walls  are  saturated  it  makes  no  difference 

*  Though  generally  true,  it  must  not  be  supposed  that  the  fibres  of  all  species,  or 
even  the  fibres  of  the  same  tree,  shrink  exactly  in  proportion  to  the  thickness  of  their 
walls. 


228 


THE  MATERIALS  OF  CONSTRUCTION. 


in  the  volume  of  a  block  of  pine  wood  whether  the  cell-cavities  are  empty 
as  in  the  heartwood  or  three  fourths  filled  as  in  the  sapwood. 

If  an  entire  fibre,  as  shown  in  Fig.  101,  is  dried,  the  wall  at  its  ends 
a  and  b,  like  those  of  the  sides,  grows  thinner,  and  thereby  the  length  of 
the  entire  cell  grows  shorter.  Since  this  length  is  often  a  hundred  or 
more  times  as  great  as  the  diameter,  the  effect  of  this  shrinkage  is  inap- 
preciable; and  if  a  long  board  shrinks  lengthwise,  it  is  largely  due,  as 
we  shall  see,  to  quite  another  cause. 

A  thin  cross-section  of  several  fibres  (see  Fig.  102,  A)  like  the  piece 
of  a  single  fibre  shrinks  when  dried,  the  wall  of  each  fibre  becomes 


FIG.  101. 
Isolated  Cell. 


FIG.    10'2.— Warping    of 
Wood. 


thinner,  and  thus  each  piece  smaller,  and  the  piece  on  the  whole  necessarily 
shares  this  diminution  of  size,  the  distances  ab  and  cd  each  becoming 
shorter.  Where  the  cells  are  very  similar  in  size  and  in  the  thickness  of 
their  walls,  as  in  the  case  of  piece  A,  Fig.  102,  ab  and  cd  become  shorter 
by  about  the  same  amount ;  but  if  the  piece  is  made  up  of  fibres  some 
of  which  have  thin  and  others  thick  walls,  as  piece  B,  Fig.  102,  then,  the 
row  of  thick-walled  cells  shrinking  much  more  than  the  row  of  thin-walled 
cells,  the  piece  becomes  unevenly  shrunk  or  warped  as  shown  in  Fig.  102, 
C.  Not  only  is  the  piece  warped,  but  the  force  which  led  to  this  warping 
continues  to  strain  the  interior  parts  of  the  piece  in  different  directions. 

Since  in  all  our  woods  cells  with  thick  walls  and  cells  with  thin  walls 
are  more  or  less  intermixed,  and  especially  as  the  spring  wood  and  summer 
wood  nearly  always  differ  from  each  other  in  this  respect,  strains  and 
tendencies  to  warp  are  always  active  when  wood  dries  out,  because  the 
summer  wood  shrinks  more  than  the  spring  wood,  heavier  wood  in  general 
more  than  li^ht  wood  of  the  same  kind. 


TIMBER. 


229 


X 


If  the  piece  A,  Fig.  102,  after  drying  is  placed  edgewise  on  moist  blot- 
ting-paper, the  cells  on  the  under  side,  at  cd,  take  up  moisture  from  the 
paper  and  swell  before  the  upper  cells  at  ab  re- 
ceive any  moisture.  This  causes  the  under  side  ^ 
of  the  piece  to  become  longer  than  the  upper 
side,  and,  as  in  the  case  of  piece  C,  warping  c 
occurs.  Soon,  however,  the  moisture  penetrates 
to  all  the  cells  and  the  piece  straightens  out.  A 
thin  board  behaves  exactly  like  this  minute 
piece,  only  the  process  is  slower  and  more  easily 
observed.  But  while  a  thin  board  of  pine  curves 
laterally,  it  remains  quite  straight  lengthwise, 
since  in  this  direction  both  shrinkage  and  swell- 
ing are  small.  A  thin  disk  or  cross-section 
swells,  and  when  moistened  on  one  side  warps  as 
readily  in  one  direction  as  in  another.  If  a  green 
board  is  exposed  to  the  sun  upon  one  side,  warp- 
ing is  produced  by  removal  of  water  and  conse- 
quent shrinkage  of  that  side,  and  the  course  of 
the  process  is  simply  reversed. 

As  already  stated,  wood  loses  water  faster 
from  the  end  than  from  the  longitudinal  faces. 
Hence  the  ends  shrink  at  a  different  rate  from 
the  interior  parts. 

195.  Effects  of  Shrinkage.— In  a  timber,  the  width  AB  (Fig.  103,  X) 
may  have  shortened  (Fig.  21,  Y),  while  a  short  distance  from  the  end  cd 
the  original  width  is  still  preserved.  This  should  produce  a  bending  of 
the  parts  toward  the  centre  of  the  piece  as  shown  in  exaggeration  at  Y,  but 
the  rigidity  of  the  several  parts  of  the  t.i-.iber  prevents  such  bending  and 
the  consequent  strain  leads  to  their  separation  as  shown  at  Z,  the  end  sur- 
face of  the  timber  being  "  checked." 

As  the  timber  dries  out,  the  line  cd  becomes  shorter,  the  parts  1  to  6 
are  allowed  to  approach  again,  and  the  checks  close  up  and  are  no  longer 
visible. 

The  faster  the  drying  at  the  surface,  the  greater  is  the  difference  in  the 
moisture  of  the  different  parts,  and  hence  the  greater  the  strains  and  con- 
sequently also  the  amount  of  checking.  This  becomes  very  evident  when 
fresh  wood  is  placed  in  the  sun,  and  still  more  in  a  hot  kiln.  While  most 
of  these  smaller  checks  are  thus  only  temporary,  closing  up  again,  some 
large  radial  checks  remain  and  even  grow  larger  as  drying  progresses. 
Their  cause  is  a  different  one  and  will  presently  be  explained. 

The  temporary  checks  not  only  occur  at  the  ends,  but  are  developed  on 
the  sides  also,  only  to  a  much  smaller  degree.  They  become  especially  an- 


FIG. 


103.— Formation    of 
Checks. 


230 


THE  MATERIALS -OF  CONSTRUCTION. 


noying  on  the  surface  of  thick  planks  of  hard  woods,  and  also  on  peeled 

logs  when  exposed  to  the  sun. 

So  far  we  have  considered  the  wood 
as  if  made  up  only  of  parallel  fibres  all 
placed  longitudinally  in  the  log.  This, 
however,  is  not  the  case.  A  large  part  of 
the  wood  is  formed  by  the  medullary  or 
pith  rays.  In  pine  over  15,000  of  these 
occur  on  a  square  inch  of  a  tangential  sec- 
tion, and  even  in  oak  the  very  large  rays, 
which  are  readily  visible  to  the  eye,  repre- 
sent  scarcely  a  hundredth  part  of  the  num- 
ber which  the  microscope  reveals. 

As  seen  in  Fig.  104,  the  cells  of  these 
rays  have  their  length  at  right  angles  to 
the  direction  of  the  wood-fibres. 

If   a  large   pith-ray  of   white   oak   is 

whittled   out   and   allowed   to  dry,  it    is 

...  /  '       . 

found  to  shrmk  S^^J  m  the  direction 
from  c  to  d  (Fig.  104),  while,  as  we  have 
stated,  the  fibres  to  which  the  ray  is 
firmly  grown  in  the  wood  do  not  shrink  in  the  same  direction.  There- 
fore, in  the  wood,  as  the  cells  of  the  pith-ray  dry,  they  pull  on  the  longitu- 
dinal fibres  and  try  to  shorten  them,  and,  being  opposed  by  the  rigidity  of 
the  fibres,  the  pith-ray  is  greatly  strained.  But  this  is  not  the  only  strain 
it  has  to  bear.  Since  the  fibers  from  a  to  b  (Fig.  104)  shrink  as  much 
again  as  the  pith-ray  in  this,  its  longitudinal  direction,  the  fibres  tend  to 
shorten  the  ray,  and  the  latter,  in  opposing  this,  prevents  the  former  from 
shrinking  as  much  as  they  otherwise  would.  Thus  the  structure  is  sub- 
jected to  severe  strains  at  right  angles  to  each  other;  and  herein  lies  the 
greatest  difficulty  of  wood-seasoning,  for  whenever  the  wood  dries  rapidly 
these  fibres  have  not  the  chance  to  '  '  give  "  or  accommodate  themselves, 
and  hence  fibres  and  pith-rays  separate  and  checks  result  which,  whether 
visible  or  not,  are  detrimental  in  the  use  of  the  wood. 

The  contraction  of  the  pith-rays  parallel  to  the  length  of  the  board  is 
probably  one  of  the  causes  of  the  small  amount  of  longitudinal  shrinkage 
which  has  been  observed  in  boards.*  The  smaller  shrinkage  of  the  pith- 
rays  along  the  radius  of  the  log  (the  length  of  the  pith-ray)  opposing  the 
shrinkage  of  the  fibres  in  this  direction  becomes  one  of  the  causes  of  the 
second  great  trouble  in  wood-seasoning,  namely,  the  difference  in  the 


FIG.  104.—  Small  Pith-ray  m  Oak.  a, 
6,  wood-fibres;  c,  d,  cells  of  pith- 
rav 


*  In  addition  to  this  all  fibres  having  an  oblique  position,  as  those  at  pith-rays  and 
knots,  also  the  oblique,  tapering  ends^all  fibers,  contribute  to  this  longitudinal  shrink- 
age, since  one  component  of  their^rrrm)  shrinkage  is  longitudinal. 


TIMBER. 


231 


FIG.     105.— Effects 
of  Shrinkage. 


amount  of   the  shrinkage  along  the   radius   and  that  along  the  rings   or 
tangent. 

This  greater  tangential  shrinkage  appears  to  be  due, 
in  part,  to  the  cause  just  mentioned,  but  also  to  the  fact 
that  the  greatly  shrinking  bands  of  summer  wood  are 
interrupted,  along  the  radius,  by  as  many  bands  of  porous 
spring  wood,  while  they  are  continuous  in  the  tangential 
direction.  In  this  direction,  therefore,  each  such  band 
tends  to  shrink,  as  if  the  entire  piece  were  composed  of 
summer  wood;  and  since  the  summer  wood  represents  the 
greater  part  of  the  wood-substance,  this  tendency  of 
greater  tangential  shrinkage  prevails. 

The  effect  of  this  greater  tangential  shrinkage  affects 
every  phase  of  woodworking.  It  lead£  to  permanent 
checks,  and  causes  the  log  to  split  open  on  drying. 

Sawed  in  two,  the  flat  sides  of  the  log  become  convex, 
as  in  Fig.  105;  sawed  into  a  timber,  it  checks  along  the 
median  line  of  the  four  faces,  and  if  converted  into 
boards  the  latter  take  on  the  forms  shown  in  Fig.  105, 
all  owing  to  the  greater  tangential  shrinkage  of  the  wood. 

Briefly,  then,  shrinkage  of  wood  is  due  to  the  fact 
that  the  celL walls  grow  thinner  on  drying.  The  thicker  cell-walls  and  there- 
fore the  heavier  wood  shrinks  most,  while  the  water  in  the  cell-cavities  does 
not  influence  the  volume  of  the  wood.  Owing  to  the  great  difference  of 
cells  in  shape,  size,  and  thickness  of  walls,  and  still  more  in  their  arrange- 
ment, shrinkage  is  not  uniform  in  any  kind  of  wood.  This  irregular  defor- 
mation produces  stresses  which  grow  with  the  difference  between  adjoining 
cells  and  are  greatest  at  the  pith-rays.  These  deformations  cause  warping 
and  checking,  and  exist  even  when  no  outward  signs  are  visible;  they  are 
greater  if  the  wood  is  dried  rapidly  than  if  dried  slowly,  but*  can  never  be 
entirely  avoided. 

Temporary  checks  are  caused  by  the  more  rapid  drying  of  the  outer  parts 
of  any  stick;  permanent  checks  are  due  to  the  greater  shrinkage,  tangen- 
tially,  along  the  rings  than  that  along  the  radius.  This,  too,  is  the  cause  of 
most  of  the  ordinary  phenomena  of  shrinkage,  such  as  the  difference  in 
behavior  of  entire  and  quartered  logs,  "bastard"  (tangent)  and  "rift" 
(radial)  boards,  etc.,  and  explains  many  of  the  phenomena  erroneously  attrib- 
uted to  the  influence  of  the  bark,  or  of  the  greater  shrinkage  of  outer  and 
inner  parts  of  any  log. 

Once  dry,  wood  may  be  swelled  again  to  its  original  size  by  soaking  in 
water,  boiling,  or  steaming.  Soaked  pieces,  on  drying,  shrink  again  as 
before;  boiled  and  steamed  pieces  do  the  same,  but  to  a  slightly  less  degree. 
Neither  hygroscopicity,  i.e.,  the  capacity  of  taking  up  water,  nor  shrinkage  of 
Wood  can  be  overcome  by  drying  at  temperatures  below  200°-F.  Higher 


232  THE  MATERIALS  OF  CONSTRUCTION. 

temperatures,  however,  reduce  these  qualities,  but  nothing  short  of  a  coaling 

heat  robs  wood  of  the  capacity  to  shrink  and 
swell.     Rapidly  dried  in  the  kiln,  the  wood  of 
oak  and  other  hard  woods  "  caseharden,"  that 
is,  the  outer  part  dries  and  shrinks  before  the 
interior  has  a  chance  to  do  the  Fame,  and  thus 
FIG.    106. —"  Honeycombed  "    forms  a  firm  s}ien  or  case  Of  shrunken,  corn- 
Board      The  checks  or  cracks    mo]lly  checked  wood  around  the  interioi,   This 
form  along  the  pith-rays.  in-,  -i      •    ,     •       <. 

shell  does  not  prevent  the  interior  irorn  dry- 
ing, but  when  this  drying  occurs,  the  interior  is  commonly  checked  along 
the  medullary  rays,  as  shown  in  Fig.  106.  In  practice  this  occurrence  can  be 
prevented  by  steaming  the  lumber  in  the  kiln,  and  still  better  by  drying  the 
wood  in  the  open  air  or  in  a  shed  before  placing  in  the  kiln.  Since  only 
the  first  shrinking  is  apt  to  check  the  wood,  any  kind  of  lumber  which  has 
once  been  air  dried  (three  to  six  months  for  1-inch  stuff)  may  be  subjected 
to  kiln-heat  without  any  danger.  Kept  in  a  bent  or  warped  condition  during 
the  first  shrinking,  the  wood  retains  the  shape  to  which  it  was  bent  and 
firmly  opposes  any  attempt  at  subsequent  straightening. 

196.  Amount  of  Shrinkage  in  Timber. — Sapwood,  as  a  rule,  shrinks  more 
than  heartwood  of  the  same  weight,  but  very  heavy  heartwood  may  shrink 
more  than  lighter  sapwood.  The  amount  of  water  in  wood  is  no  criterion  of 
its  shrinkage,  since  in  wet  wood  most  of  the  water  is  held  in  the  cavities, 
where  it  has  no  effect  on  the  volume. 

The  wood  of  pine,  spruce,  cypress,  etc.,  with  its  very  regular  structure,  dries 
and  shrinks  evenly  and  suffers  much  less  in  seasoning  than  the  wood  of 
broad-leaved  trees.  Among  the  latter,  oak  is  the  most  difficult  to  dry  with- 
out injury.  Small-sized  split  ware  and  "rift"  boards  season  better  than 
ordinary  boards  and  planks. 

To  avoid  "working"  or  warping  and  checking,  all  high-grade  stock  is 
carefully  seasoned,  preferably  in  a' kiln,  before  manufacture.  Thicker  pieces 
may  be  made  of  several  parts  glued  together;  larger  surfaces  are  made  in 
panels  or  of  smaller  pieces  covered  with  veneer.  Boring  is  sometimes  resorted 
to  to  prevent  the  checking  of  wooden  columns. 

Since  repeated  swelling  increases  the  injuries  due  to  seasoning,  wood 
should  be  protected  against  moisture  when  once  it  is  dry. 

Since  the  shrinkage  of  our  woods  has  never  been  carefully  studied,  and 
since  wood,  even  from  the  same  tree,  varies  within  considerable  limits,  the 
figures  given  in  the  following  table  are  to  be  regarded  as  mere  approximations. 
The  shrinkage  along  the  radius  and  that  along  the  tangent  (parallel  to  the 
rings)  are  not  stated  separately  in  the  following  table,  and  the  figures  repre- 
sent an  average  of  the  shrinkage  in  the  two  directions.  Thus,  if  the  shrink- 
age of  soft  pine  is  given  at  3  inches  per  hundred,  it  means  that  the  sum  of 
radial  and  tangential  shrinkage  is  about  6  inches,  of  which  about  4  inches  fall 


TIMBER.  233 

to  the  tangent  and  2  inches  to  the  radius,  the  ratio  between  these  varying 
from  3  to  2,  a  ratio  which  practically  prevails  in  most  of  our  woods. 

Since  only  an  insignificant  longitudinal  shrinkage  takes  place  (being 
commonly  less  than  0. 1  inch  per  hundred,  though  in  oak  it  is  much  more),  the 
change  in  volume  during  drying  is  about  equal  to  the  sum  of  the  radial  and 
tangential  shrinkage,  or  twice  the  amount  of  linear  shrinkage  indicated  in 
the  table. 

Thus,  if  the  linear  average  shrinkage  of  soft  pine  is  3  inches  per  hun- 
dred, the  shrinkage  in  volume  is  about  6  cubic  inches  for  each  100  cubic 
inches  of  fresh  wood,  or  6  per  cent  of  the  volume. 

APPROXIMATE    SHRINKAGE   OF   A    BOARD,    OR    SET   OF   BOARDS,    100   INCHES 
WIDE,    DRYIXG    IN   THE    OPEN   AIR. 

Lateral 

Common  Names  of  Species.  Shrinkage 

Inches. 

(1)  All  light  conifers  (soft  pine,  spruce,  cedar,  cypress) 3 

(2)  Heavy  conifers  (hard  pine,  tamarack,  yew),  honey-locust,  box-elder,  wood 

of  old  oaks 4 

(3)  Ash,  elm,  walnut,  poplar,  maple,  beech,  sycamore,  cherry,  black  locust..  5 

(4)  Basswood,  birch,  chestnut,  horse  chestnut,  blue  beech,  young  locust 6 

(5)  Hickory,  young  oak,  especially  red  oak Up  to  10 

MECHANICAL  PROPERTIES  OF  WOOD.* 

197.  General  View. — Every  joist  and  studding,  every  rafter,  sash,  and 
door,  the  chair  we  sit  on,  the  floor  we  walk  on,  the  wood  of  the  wagon  or 
boat  we  ride  in,  are  all  continually  tested  as  to  their  stiffness  and  strength, 
their  hardness  and  toughness.  Every  step  from  the  simple  splitting  of  a 
shingle  or  stave  to  the  construction  of  the  most  elegant  carriage  or  side- 
board involves  a  knowledge  not  only  of  one,  but  of  several,  of  the  mechani- 
cal properties  of  the  material. 

In  the  shop  the  fitness  of  the  wood  for  a  given  purpose  never  depends  on 
any  one  quality  alone,  but  invariably  upon  a  combination  of  several  quali- 
ties. A  spoke  must  not  only  be  strong,  it  must  be  stiff  to  hold  its  shape,  it 
must  be  tough  to  avoid  shattering  to  pieces,  and  it  must  also  be  hard  or  else 
its  tenons  will  become  loose  in  their  mortises. 

Selecting  wood  in  this  way,  the  woodworker  has  learned  almost  all  that 
is  at  present  known  about  his  material;  but  in  many  cases  the  great  diffi- 
culty which  always  attends  the  judgment  of  complex  phenomena  has  led  to 
erroneous  conclusions,  and  not  a  few  well-established  beliefs  have  their  origin 
more  in  accidental  errors  of  observation  than  in  fact. 

The  experimenter  endeavors  to  avoid  this  complexity  by  testing   the 

*  This  section  of  the  Bulletin  was  made  very  simple  for  popular  comprehension.  It 
seems  somewhat  out  of  place,  therefore,  in  a  scientific  work,  but  is  retained  here  for  the 
sake  of  completeness.— J.  B.  J. 


234  THE  MATERIALS  OF  CONSTRUCTION. 

wood  for  each  kind  of  resistance  separately;  when  tested  as  to  their  stiff- 
ness, the  pieces  are  all  shaped,  placed,  and  loaded  alike.  The  wood  is 
selected  with  a  definite  object  in  view;  it  is  green  or  dry,  clear  or  knotty, 
straight  or  cross-grained,  according  as  he  wishes  to  find  out  the  influence  of 
each  of  these  conditions.  If  pine  and  oak  are  to  be  compared,  the  pieces 
are  from  the  same  position  in  the  tree  and  are  tried  under  exactly  the  same 
'conditions,  and  thus  the  case  is  simplified. 

But  even  results  thus  arrived  at  cannot  be  used  indiscriminate!}^  and 
the  figures  on  the  strength  of  oak  given  in  any  book  must  not  be  supposed 
to  apply  to  all  oak  if  tested  in  the  given  manner.  This  is  due  to  the  fact 
that  a  piece  of  wood  is  not  simply  a  material  but  a  structure,  just  as  much 
as  a  railroad-bridge  or  a  balloon  frame,  and  as  such  varies  greatly  even  in 
the  wood  of  the  same  tree,  nay,  more  than  that,  even  in  the  same  year's 
growth  of  the  same  cross-section  of  a  log. 

A  scantling  resists  bending;  it  is  stiff.  On  removal  of  the  load  it 
straightens;  it  is  elastic.  A  column,  a  prop,  or  the  spoke  of  a  wagon-wheel 
resists  being  crushed  endwise.  So  does  the  upper  side  of  a  joist  or  beam 
when  loaded,  while  the  under  side  of  the  beam  or  of  an  axe-handle  suffers  in 
tension.  The  tenons  of  a  window  sash  or  of  a  door  tend  to  break  out  their 
mortises,  the  wood  has  to  resist  shearing  along  the  fibres;  the  steel  edge  of 
the  eye  tends  to  cut  into  the  hammer-handle,  it  tries  to  shear  it  across- the 
grain,  and  every  nail,  screw,  bore-hole,  or  mortise  tends  to  split  the  board 
and  tries  the  wood  as  to  its  cleavability,  while  all  "bent"  ware,  from  the 
wicker  basket  to  the  one-piece  felly  or  ship's  knee,  involves  its  flexibility. 

198.  Stiffness. — If  100  pounds  placed  in  the  middle  of  a  stick  2  by 
inches  and  4  feet  long,  supported  at  both  ends,  bend  or  "deflect"  this 
stick  one  eighth  of  an  inch  (in  the  middle),  then  200  pounds  will  bend  it 
about  one-fourth  inch,  300  pounds  three-eighths  inch,  the  deflection  varying- 
directly  as  the  load.  Soon,  however,  a  point  is  reached  where  an  additional 
100  pounds  adds  more  than  one-eighth  inch  to  the  deflection — the  limit  of 
elasticity  has  been  reached.  Taking  another  piece  from  the  straight-grained 
and  perfectly  clear  plank  of  the  same  depth  and  width,  but  8  feet  long,  the 
load  of  100  pounds  will  cause  it  to  bend  not  only  one-eighth  inch,  but  will 
deflect  it  by  about  1  inch.  Doubling  the  length  reduces  the  stiffness  eight- 
fold. Stiffness  then  decreases  as  the  cube  of  the  length. 

Cutting  out  a  piece  2  by  4  inches  and  4  feet  long,  placing  it  flatwise  so 
that  it  is  double  the  width  of  the  former  stick,  and  loading  it  with  100 
pounds,  we  find  it  bending  only  one-sixteenth  inch:  doubling  the  width 
doubles  the  stiffness. 

Setting  the  same  2  X  4-inch  piece  on  edge,  so  that  it  is  2  inches  wide 
and  4  inches  deep,  the  load  of  100  pounds  bends  it  only  about  one  sixty- 
fourth  inch:  doubling  the  thickness  increases  the  stiffness  about  eightfold. 

It  follows  that  if  we  double  the  length  and  wish  to  retain  the  same 
stiffness  we  must  also  double  the  thickness  of  the  piece. 


TIMBER.  235 

A  piece  of  wood  is  usually  stiffer  with  the  annual  rings  set  vertically 
than  if  the  rings  are  placed  horizontally  to  the  load. 

Cross-grained  and  knotty  wood,  to  be  sure,  is  not  as  stiff  as  clear  lumber; 
a  knot  on  the  upper  side  of  a  joist,  which  must  resist  in  compression,  is, 
however,  not  so  detrimental  as  a  knot  on 
the  lower  side,  where  it  is  tried  in  tension, 


Every  large  timber  which  comes  from  A 


--~—' 


3 


the  central  part  of  the  tree  contains  knots, 

and  much  of  its  wood  is  cut  more  or  less      ^^  ^ 

,.,.  FIG.  107.— Bending  a  Beam, 

obliquely  across  the  grain,  both  conditions 

rendering  such  material  comparatively  less  stiff  than  small  clear  pieces. 

The  same  stick  of  pine  green  or  wet  is  only  about  two  thirds  as  stiff  as 
when  dry.  A  heavy  piece  of  long-leaf  pine  is  stiffer  than  a  light  piece; 
heavy  pine  in  general  is  stiffer  than  light  pine,  but  a  piece  of  hickory, 
although  heavier  than  the  pine,  may  not  be  as  stiff  as  the  piece  of  long-leaf 
pine;  and  a  good  piece  of  larch  exceeds  in  stiffness  any  oak  of  the  same 
weight. 

(  In  the  same  tree  stiffness  varies  with  the  weight,  the  heavier  wood  being 
the  stiffer;  thus  the  heavier  wood  of  the  butt  log  is  stiffer  than  that  of  the 
top;  timber  with  much  of  the  heavy  summer  wood  is  stiffer  than  timber  of 
the  same  kind  with  less  summer  wood.  In  old  trees  (of  pine)  the  centre  of 
the  tree  and  the  sap  are  the  least  stiff;  in  thrifty  young  pine  the  centre  is 
the  least  stiff,  but  in  young  second-growth  hard  woods  it  is  the  stiffest. 

Since  it  is  desirable,  and  for  many  purposes  essential,  to  know  before- 
hand that  a  given  piece  with  a  given  load  will  bend  only  a  given  amount, 
the  stiffness  of  wood  is  usually  stated  in  a  uniform  manner  and  under  the 
term  "  modulus  (measure)  of  elasticity." 

If  AB,  Fig.  107,  is  a  piece  of  wood,  and  d  the  deflection  produced  by  a 
weight  or  load,  the  stiffness  of  the  wood,  as  usually  stated,  is  found  by  the 
formula 

wr 

Modulus  of  elasticity  —  E  =      .  ,  a,[ 

where  W  is  the  weight,  I  the  length,  b  and  li  the  breadth  and  depth  (height) 
of  the  stick,  and  d  the  deflection  for  the  load  W  In  the  following  table 
the  woods  are  grouped  according  to  their  stiffness.  The  figures  are  only 
rough  approximations  which  are  based  on  the  data  given  in  Vol.  IX  of  the 
Tenth  Census.  The  first  column  contains  the  above  modulus,  the  second 
shows  how  many  pounds  will  produce  a  deflection  of  1  inch  in  a  stick  1  by  1 
by  12  inches,  assuming  that  it  could  endure  such  bending  within  the  limits 
of  elasticity,  and  the  third  column  gives  the  number  of  pounds  which  will 
bend  a  stick  2  by  2  inches  and  10  feet  long  through  1  inch. 

The  stick  is  assumed  to  rest  on  both  ends;  if  it  is  a  cantilever,  i.e ,  fas- 
tened at  one  end  and  loaded  at  the  other,  it  bears  but  half  as  much  load 
at  its  end  for  the  same  deflection. 


236 


TEE  MATERIALS  OF  CONSTRUCTION. 


Prom  the  third  column  it  is  easy  to  find  how  many  pounds  would  bend 
a  piece  of  the  same  kind  of  other  dimensions.  A  2  X  4-inch  bears  eight, 
a  2  X  6-inch  twenty-seven  times  as  much  as  the  2  X  2-inch;  a  piece  8  feet 
long  is  about  twice  as  stiff  as  a  10-foot  piece;  a  piece  12  feet  only  about 
three  fifths,  14  feet  one  third,  16  feet  two  ninths,  18  feet  one  sixth,  and  20 
feet  one  eighth  as  stiff. 

The  number  of  pounds  which  will  bend  any  piece  of  sawed  timber  by  1 
inch  may  be  found  by  using  the  formula 

.  ,  . 
JNecessary  weight  = 


~     , 

where  E  is  the  figure  in  the  first  column,  and  b,  li,  I,  the  breadth,  depth,  and 
length  of  the  timber  in  inches.  If  the  deflection  is  not  to  exceed  one-half 
inch,  only  one  half  this  load,  and  if  one-fourth  inch,  only  one  fourth  this  loadj 

is  permissible;  or,  in  general,  W  =  —  ;^  —  ,  where  d  is  the  deflection  in  inches. 

CvO 

TABLE   OF   STIFFNESS  (MODULUS   OF  ELASTICITY)  OF   DRY   WOOD. 
GENERAL   AVERAGES. 


Species. 

Modulus  of 
Elasticity 
Wl* 

Approximate  Weight 
which  deflects  by 
Inch  a  Piece 

4d6/i3 

per  Square 
Inch. 

1  by  1  Inch 
and 
12  In.  long. 

2  by  2  In. 
and 
10  Ft.  long. 

Pounds. 

62 

51 

40 
37 

(1)  Live  oak,  good  tamarack,  long-leaf,  Cuban,  and  short- 
leaf  pine,  good  Douglas  spruce,  Western  hemlock, 
yellow  and  cherry  birch,  hard  maple,  beech,  locust, 
and  the  best  of  oak  and  hickory  ... 

Pounds. 

1,680,000 
1,400,000 

1,100,000 
1,000,000 

Pounds 

3,900 
3,200 

2,500 
2,300 

(2)  Birch,  common  oak,  hickory,  white  and  black  spruce, 
loblolly  and  red  pine,  cypress,  best  of  ash,  elm,  and 
poplar  and  black  walutit  

(3)  Maples,  cherry,  ash,  elm,  sycamore,  sweet  gum,  but- 
ternut,  poplar,   basswood,  white,  sugar,  and   bull 
pine,  cedars,  scrub  pine,  hemlock,  and  fir  
(4)  Box-elder,  horse-chestnut,  a  number  of  Western  soft 
pines  inferior  grades  of  hard  woods  

199.  Cross-breaking  or  Bending  Strength. — When  the  addition  of  100 
pounds  to  the  load  on  our  2  X  2-inch  piece  begins  to  add  more  than  one 
eighth  inch  to  the  deflection,  that  is,  when  the  stick  has  been-  bent  beyond 
its  "elastic  limit/'  it  still  requires  an  increase  of  30  to  50  per  cent  to  the 
load  before  the  stick  breaks.  The  load  which  is  borne  before  the  limit  of 
elasticity  is  reached  indicates  the  strength  of  the  wood  up  to  this  important 
point;  the  load  which  causes  it  to  break  represents  its  absolute  strength,  or 
the  "cross-breaking  or  bending  strength"  as  it  is  commonly  called. 

In  long-leaf  pine  the  former  (modulus  of  strength  at  the  elastic  limit)* 

*  The  ;:  elastic  limit  "  in  this  case  is  somewhat  of  an  arbitrary  quantity,  namely,  the 
point  where  100  pounds  produces  a  deflection  50  par  cent  greater  than  the  first  100 

pounds. 


xx««««,  237 


is  commonly  about  three  fourths  of  the  latter.  If  left  loaded  for  a  consid- 
time,  a  load  even  less  than  that  which  brings  the  stick  to  its  elastic  limit 
will  cause  it  to  break,  and  this  load  should  therefore  not  be  reached  in  prac- 
tice. 

Unlike  the  stiffness,  the  strength  of  a  timber  varies  approximately  with 
the  squares  of  the  thickness  and  decreases  directly  with  increasing  length  and 
not  with  the  cube  of  this  latter  dimension.  Thus  if  our  piece  2  by  2  inches 
and  4  feet  long  can  bear  1000  pounds  before  it  breaks,  a  2  X  4-inch  laid 
flat  will  break  with  about  2000  pounds,  and  if  set  edgewise  it  requires  about 
4000  pounds  to  break  it,  while  a  piece  of  the  same  kind  2  by  2  inches  and 
double  the  length  (8  feet)  breaks  with  half  the  original  load,  or  only  500 
pounds. 

All  conditions  of  the  material  which  influence  the  stiffness  also  influ- 
ence the  bending  strength.  Seasoning  increases,  moisture  decreases,  the 
strength;  knots  and  cross-grain  depress  it,  and  both  are  more  dangerous  on 
the  lower  than  on  the  upper  side.  But  while  the  conifers  with,their  sim- 
ple cell-structure  excel  in  stiffness,  the  better  hard  woods  develop  the 
greater  strength  in  bending.  Like  elasticity  and  stiffness,  the  strength  is 
expressed  in  a  uniform  manner  by  the  so-called  "modulus  of  rupture,"  to 
permit  ready  estimation  of  the  strength  of  any  given  piece.  This  modulus 
refers  to  the  resistance  per  square  inch  which  the  parts  most  strained, "  the 
extreme  fibre,"  offer.  The  figures  usually  tabulated  are  obtained  by  the 
formula 

3  TT7 
Strength  per  square  inch  of  extreme  fibre  =  /  =  ^TTTJ 

where  W  is  the  breaking-load,  I  the  length,  ~b  and  li  the  breadth  and  depth 
of  the  tested  piece  of  wood. 

The  following  table  presents  our  common  woods  grouped  as  to  their 
strength  in  bending.  The  load,  as  before,  is  supposed  to  act  altogether  in 
the  middle.  Column  1  gives  the  strength  of  the  extreme  fibre,  as  explained 
above;  column  2,  the  number  of  pounds  which  will  break  a  piece  1  by  1  inch 
and  12  inches  long;  and  column  3,  the  strength  of  a  stick  2  by  2  inches  and 
10  feet  long:  from  which  the  strength  of  any  given  piece  can  readily  be  esti- 
mated, allowing,  however,  for  defects,  which  increase  with  the  size.  Tims, 
if  a  good  piece  of  pine  2  by  2  inches  and  10  feet  long  breaks  with  400  pounds, 
a  2  X  4-inch  set  on  edge  requires  1600  pounds,  a  2  X  6-inch,  3600  pounds, 
a  2  x  8-inch  piece  6400  pounds  to  break  it.  If  a  piece  2  by  4  inches  and 
10  feet  long  breaks  with  1600  pounds,  a  2  X  4-inch  and  12  feet  long  piece 
breaks  with  about  1300  pounds,  one  16  feet  with  1000  pounds,  etc. ;  and  if 
a  factor  of  safety  of  10  is  allowed,  only  one  tenth  of  the  above  loads  are 
permissible. 

A,  board  \  inch  by  12  indies  and  10  feet  long  contains  as  much  wood 
as  a  3  x  2-inch  of  the  same  length,  and  if  placed  edgewise  should  offer 
four  times  as  much  resistance  to  breaking.  Owing  to  its  small  breadth, 


238 


THE  MATERIALS  OF  CONSTRUCTION. 


however,  it  "twists"  when  loaded,  and  in  most  cases,  therefore,  bears 
less  than  the  2  x  3-inch.  To  prevent  this  twisting,  joists  are  braced,  and 
the  depth  of  timbers  is  made  not  to  exceed  four  times  their  thickness. 

Short  deep  pieces  shear  out  or  split  before  their  strength  in  bending  can 
fully  be  called  into  play. 

To  allow  for  normal  irregularities  in  the  structure  of  wood  itself,  as  well 
as  in  the  aggregate  structure  of  timbers,  an  allowance  is  made  on  the  num- 
bers which  have  been  found  by  experiment;  this  allowance  is  called  the  "  fac- 
tor of  safety."  Where  the  selection  of  the  wood  is  not  very  perfect,  the  load 
is  a  variable  one,  and  the  safety  of  human  life  depends  on  the  structure,  the 
factor  is  usually  taken  quite  high,  as  much  as  G  or  10;  i.e.,  only  one  sixth  or 
one  tenth  of  the  figures  given  iu  the  tables  is  considered  safe,  and  the  beam 
is  made  six  to  ten  times  as  heavy  as  the  calculation  requires. 


STRENGTH 


CROSS-BREAKING    OF   WELL-SEASONED    SELECT    PIECES. 


Common  Names  of  Species. 

Strength  of 
the  Extreme 
Fibre 
3  Wl 
'  ~  2bli* 
per  Square 
Inch. 

Approximate  Weight 
which  breaks  a  Stick 

1  by  1  Inch 

and  12  Inches 
long. 

2  by  2  Inches 
and  10  Feet 
long. 

(1)  Robinia  (locust),  hard  maple,  hickory,  oak,  birch, 
best  ash  and  elm,  long-leaf,  short-  leaf,  and 

Pounds. 
13  000 

Pounds. 

720 

550 
350 

Pounds. 
570 

440 

280 

(2)  Soft  maple,  cherry,  ash,  elm,  walnut,  iuferioi 
oak  and  birch,  best  poplar,  Norway,  loblolly, 
and  pitch  pines,  black  and  white  spruce,  hem- 
lock and  tjood  cedar  .  .  .  .  . 

10,000 

6,500 

(3)  Tulip,  basswood,  sycamore,  butternut,  poplars, 
white  and  other  soft  pines,  firs,  and  cedars.  .  . 

200.  Tension  and  Compression. — When'a  piece  of  wood  is  pulled  length- 
wise, in  the  manner  shown  in  Fig.  108,  part  of  the  fibres  are  torn  asunder 
or  broken,  but  many  are  merely  pulled  or  shredded  out  from  between  their 
neighbors.  Since  failure  in  tension  thus  involves  lateral  adhesion  as  well 
as  strength  of  fibres,  it  is  affected  not  only  by  the  nature  and  dimensions 
of  the  fibres,  but  also  by  their  arrangement.  Owing  to  their  transverse 
position  the  medullary  rays  (a  large  part  of  all  woods)  offer  but  one  tenth 
to  one  twentieth  as  much  resistance  as  the  main  body  of  fibres,  and  more- 
over weaken  the  timber  by  disturbing  the  straight  course  of  the  fibres  and 
the  regularity  of  the  entire  structure. 

The  resistance  is  also  much  affected  by  the  position  of  the  grain.  The 
perfectly  cross-grained  piece  a  (Fig.  109)  sustains  but  about  one  tenth  to 
one  twentieth  of  the  load  which  is  supported  by  the  straight-grained  piece 
c,  and  it  is  evident  that  the  piece  b,  which  represents  an  excessive  degree 
of  cross -grain,  is  likewise  weakened  by  the  oblique  position  of  the  grain. 


TIMBER. 


239 


This  explains  the  detrimental  influence  of  a  knot  on  the  under  side  of  a 
board,  as  in  Fig.  110.  Since  the  lower  side  of  the  board,  in  bending,  is 
stretched,  the  upper  side  being  compressed,  the  fibres  of  the  lower  side  are 
subjected  to  tension,  and  the  wood  of  the  knot,  like  the  piece  of  cross-grained 


FIG.   109.— Straight  and  Cross- 
grained  Wood. 


FJG.  108. 
Specimen  in  Tension  Test. 


FIG.  110.— Effect  of  Knots  and  their 
Position. 


wood,  offers  but  little  resistance.  Commonly  the  defect  is  greatly  increased 
by  a  season-check  in  the  knot  itself,  so  that  the  knot  affects  the  strength 
of  the  board  like  a  saw-cut  of  equal  depth,  but  to  a  less  degree. 

Tested  in  compression  endwise  (Fig.  Ill),  the  fibres  act  as  so  many 
hollow  columns  firmly  grown  together;  and  when  the  load  becomes  too 
great  the  piece  fails  in  the  manner  illustrated  in  Fig.  113. 
This  failure  is  a  very  complex  phenomenon;  in  wood  like 
pine  the  fibres  of  the  plane  in  which  failure  occurs  become 
separated  into  small  bodies;  they  tear  apart  and  cease  to 
behave  as  one  solid  body,  but  act  as  a  large  number  of  very 
small  independent  pieces.  Like  the  strands  of  a  rope  these 
small  bodies  offer  but  little  resistance  to  compression;  they 
bend  over,  and  the  piece  "  buckles." 

It  is  evident  that  a  vertical  position  and  a  regular  ar- 
rangement of  the  fibres  increase  the  resistance,  and  that 
therefore  the  medullary  rays  and  oblique  position  of  fibres 
in  cross-grained  and  knotty  timber  tend  to  reduce  the 
strength  in  compression. 

From  the  following  table  of  strength  in  tension  and  compression  it  will 
be  seen  that  these  two  are  not  always  proportional,  the  stiffer  conifers  ex- 
celling in  the  latter,  the  tougher  hard  woods  in  the  former. 


pressioii 
wise. 


end- 


240 


TEE  MATERIALS  OF  CONSTRUCTION. 


KATIO   OF    STRENGTH    IX   TENSION"   AND    COMPRESSION,    SHOWING   THE   DIF- 
FERENCE   BETWEEN    RIGID    CONIFERS    AND    TOUGH    HARD    WOODS. 


Name  of  Species. 

Ratio  : 
tensile  strength 

K  —    —             ;  r  • 

A  Stick  1  Square  Inch  in  Cross- 
section. 
Weight  required  to 

compressive  strength 

Pull  apart. 

Crush  endwise. 

3.7 
3.8 
2.3 
2.2 

Pounds. 
32,000 
29,000 
19,400 
17,300 

Pounds. 
8,500 
7,500 
8,600 
7,400 

Elm  

Larch 

Long-leaf  pine.  ...             

STRENGTH   IN   COMPRESSION   OF   COMMON   AMERICAN   WOODS   IN   WELL- 
SEASONED    SELECT    PIECES. 

(Approximate  weight  per  square  inch  of  cross-section  requisite  to  crush  a  piece  of  wood  endwise.) 


(1)  Black  locust,  yellow  and  cherry  birch,  hard  maple,  best  hickory,  long-leaf 

and  Cuban  pines,  and  tamarack 

(2)  Common  hickory,  oak,  birch,  soft  maple,  walnut,  good  elm,  best  ash,  short- 

leaf  and  loblolly  pines,  Western  hemlock,  and  Douglas  fir 

(3)  Ash,  sycamore,  beech,  inferior  oak,  Pacific  white  cedar,  canoe  cedar,  Law- 

sou's  cypress,  common  red  cedar,  cypress,  Norway  and  superior  spruces, 
and  fir 

(4)  Tulip,  basswood,  butternut,  chestnut,  good  poplar,  white  and  other  common 

soft  pines,  hemlock  spruce,  and  fir 

(5)  Soft  poplar,  white  cedar,  and  some  Western  soft  pines,  and  firs 


Pounds. 
9,000-h 
7,000-H 

6,000+> 

5,000+ 
4,000-f- 


201.  Shearing. — "When,  in  a  structure  like  that  shown  in  Fig.  11*2,  a 
weight  is  placed  on  /  and  the  tenon  T  by  downward  pressure  breaks  out 
the  piece  A  BCD,  this  is  said  to  shear  out  along  the  fibre.  In  the  same 
manner,  if  the  shoulder  A  BCD  in  Fig.  112  is  pushed  off  along  BD,  it  is 
sheared,  and  if  BD  and  CE  are  each  1  inch,  the  surface  thus  sheared 


FIG.  112. — Longitudinal  Shearing. 

off  is  1  square  inch,  and  the  weight  necessary  to  do  this  represents  the* 
shearing-  strength  per  square  inch  of  the  particular  kind  of  wood.  This 
resistance  is  small  when  compared  to  that  of  tension  and  compression. 


TIMBER. 


241 


116 

1 

!  4700 


B 


116 
0 
4 


FIG.  113. — Various  Forms  of  Failure.  A  and  B,  compression  endwise  ;  (7,  shearing  (the 
bolt  of  a  stirrup  passed  through  the  mortise  and  sheared  out  the  end);  D,  tension. 
The  lower  figure  indicates  the  number  of  pounds  per  square  inch  which  produced 
the  failure  in  tests  by  the  Division  of  Forestry.  No.  116  (upper  figure  on  each 
piece)  is  white  pine.  Nos.  1,  2,  and  5  are  long-leaf  pine,  about  one  fifth  natural  size. 


242  THE  MATERIALS  OF  CONSTRUCTION. 

In  general  wet  or  green  wood  shears  about  one  third  more  easily  than 
dry  wood;  a  surface  parallel  to  the  rings  (tangent)  shears  more  easily  than 
one  parallel  to  the  medullary  rays.  The  lighter  conifers  and  hard  woods 
offer  less  resistance  than  the  heavier  kinds,  but  the  best  of  pine  shears  one 
third  to  one  half  more  readily  than  oak  or  hickory,  indicating  that  great 
shearing  strengh  is  characteristic  of  "  tough  "  woods. 

RESISTANCE   TO    SHEARING    ALONG   THE    FIBRE. 

Pounds  per 
Square  Inch 

(1)  Locust,  oak,  hickory,  elm,  maple,  ash,  birch 1000  * 

(2)  Sycamore,   long-leaf,  Cuban,  and  short-leaf  pine,  and  tam- 

arack         GOO 

(3)  Tulip,   basswood,   better   class  of   poplar,    Norway,   loblolly 

and  white  pine,  spruce,  red  cedar .       400 

(4)  Softer  poplar,  hemlock,  white  cedar,  fir . .     400  \ 

NOTE. — Resistance  to  shearing,  although  a  most  important  quality  in  wood,  has  not 
been  satisfactorily  studied.  The  values  in  the  above  table,  taken  from  various  authors, 
lack  a  reliable  experimental  basis  and  can  be  considered  as  only  a  little  better  than  guess- 
work. See  Results  of  Forestry  Division  Tests  in  Chapter  XXXII. 

202.  Influence  of  Weight  and  Moisture  on  Strength. — It  has  been  stated 
that  heavy  wood  is  stronger  than  lighter  wood  of  the  same  kind,  and  that 
seasoning  increases  all  forms  of  resistance.  Let  us  examine  why  this  is  so. 

Since  the  weight  of  dry  wood  depends  on  the  number  of  fibres  and  the 
thickness  of  their  walls,  there  must  be  more  fibres  per  square  inch  of  cross- 
section  in  the  heavy  than  in  the  light  piece  of  the  same  kind,J  and  it  is  but 
natural  that  the  greater  number  of  fibres  should  also  offer  greater  resistance, 
i.e.,  have  the  greater  strength. 

The  beneficial  influence  of  drying  and  consequent  shrinking  is  twofold: 
(1)  In  dry  wood  a  greater  number  of  fibres  occur  per  square  inch,  and  (2) 
the  wood-substance  itself,  i.e.,  the  cell-walls,  become  firmer.  A  piece  of 
green  long-leaf  pine,  1  by  1  inch  and  2  inches  long,  is  only  about  0.94  by 
0.96  inch  and  2  inches  long  when  dry;  its  cross-section  is  10  per  cent 
smaller  than  before,  but  it  still  contains  the  same  number  of  fibres.  A 
dry  piece  1  by  1  inch,  therefore,  contains  10  per  cent  more  fibres  than  a 
green  piece  of  the  same  size,  and  it  is  but  fair  to  suppose  that  its  resistance 
or  strength  is  also  about  10  per  cent  greater. 

The  influence  of  the  second  factor,  though  unquestionably  the  more 
important  one,  is  less  readily  measured.  In  100  cubic  inches  of  wood-sub- 
stance the  material  of  the  cell-walls  takes  up  about  50  cubic  inches  of  water 
aud  thereby  swells  up,  becoming  about  150  cubic  inches  in  volume..  In 
keeping  with  this  swelling  the  substance  becomes  softer  and  less  resistant. 

*  Over.  f  Less  than. 

^  This  imperfect  assumption  is  used  only  for  comparison. 


TIMBER.  243 

In  pine  wood  this  diminution  of  resistance,  according  to  experiments* 
seems  to  be  about  50  per  cent,  and  the  strength  of  the  substance  therefore 
is  inversely  as  the  degree  of  saturation  or  solution. 

203.  Hardness. — Heavy  wood  is  harder  than  lighter  wood;  the  wood  of 
the  butt,  therefore,  is  harder  than  that  of  the  top,  the  darker  summer  wood 
harder  than  the  light-colored  spring  wood.     Moisture  softens,  and  season- 
ing, therefore,  hardens  wood.     Wood  is  much  harder  when  pressed  longi- 
tudinally than  when  pressed  transversely  to  the  fibres,  and  it  is  somewhat 
stronger  tangentially  than  radially.     Though  harder  wood  resists  saw  and 
chisel  more  than  softer  wood,  the  working  quality  of  the  wood  is  not  always 
a  safe  criterion  of  its  hardness. 

The  following  indicates  the  hardness  of  our  common  wroods: 

1.  Very  hard  woods  requiring  over  3200  pounds  per  square  inch  to  pro- 
duce an  indentation  of  one-twentieth   inch:    Hickory,  hard  maple,  osage 
orange,  black  locust,  persimmon,  and  the  best  of  oak,  elm,  and  hackberry. 

2.  Hard  woods  requiring  over  2400  pounds  per  square  inch  to  produce 
an  indentation  of  one-twentieth  inch:    Oak,  elm,  ash,  cherry,  birch,  black 
walnut,  beech,  blue  beech,  mulberry,  soft  maple,  holly,  sour  gum,  honey- 
locust,  coffee-tree,  and  sycamore. 

3.  Moderately  hard  woods,  requiring  over  1600  pounds  per  square  inch 
to  produce  an  indentation  of  one-twentieth  inch:  The  better  qualities  of 
Southern  and  Western  hard  pine,  tamarack  and  Douglas  spruce,  sweet  gum, 
and  the  lighter  qualities  of  birch. 

4.  Soft  woods  requiring  less  than  1600  pounds  per  square  inch  to  pro- 
duce an  indentation  of  one-twentieth  inch  V    The  greater  mass  of  conifer- 
ous woods;  pine,  spruce,  fir,  hemlock,  cedar,  cypress,  and  redwood;  poplar, 
tulip,  basswood,  butternut,  chestnut,  buckeye,  and  catalpa. 

204.  Cleavability. — When  an  axe  is  struck  into  a  piece  of  wood  as  shown 
in  Fig.  114,  the  cleft  projects  beyond  the  blade  of  the  axe  and  the  process  is 

not  one  of  cutting,  but  of  tension  across  the  grain. 
The  axe  presses  on  a  lever,  a~b,  while  the  surface  in 
which  the  transverse  tension  takes  place  is  reduced 
almost  to  a  line  across  the  stick  at  b.  If  the  wood  is 
very  stiff,  the  cleft  runs  far  ahead  of  the  axe,  the 
lever-arm  ab  is  long,  and  the  resistance  to  splitting 
proportionately  small.  A  high  modulus  of  elasticity, 
therefore,  helps  splitting,  while- great  shearing  strength, 
a  good  measure  for  transverse  tension  and  hardness, 
hinder  it. 

Wood  splits  naturally  along  two  normal  planes,  the 
most  readily  along  the  radius,  because  the  arrange- 
114.— Cleavage,  ment  of  fibres  and  pith-rays  is  radial,  and  next  along 
the  tangent,  or  with  the  annual  rings,  because  the  softer  spring  wood  forms 
continuous  planes  in  this  direction.  Cleavage  along  the  radius,  however, 


244  THE  MATERIALS  OF  CONSTRUCTION. 

is  from  50  to  100  per  cent  easier,  and  only  in  case  of  cross-grain,  etc.,  the 
cleavage  along  the  ring  becomes  the  easier.  In  the  wood  of  conifers,  wood- 
fibres  and  pith-rays  are  very  regular,  the  former  in  perfect  radial  series  or 
rows,  and  cleavage  is,  therefore,  very  easy  in  this  direction.  The  same  is 
brought  about  in  the  oak  by  the  very  wide  pith-rays,  but  where  they  are 
thick  and  narrow,  as  in  sycamore,  and  generally  in  the  butt  cuts  and  about 
knots,  they  impede  cleavage  by  causing  a  greater  irregularity  in  the  course 
of  the  wood-fibres.  The  greater  the  contrast  of  spring  and  summer  wood, 
the  easier  the  cleavage  tangentially  or  in  the  direction  of  the  rings.  This  is 
especially  marked  in  conifers  and  also  in  woods  like  oak,  ash,  and  elm,  where 
the  spring  wood  appears  as  a  continous  series  of  large  pores.  Very  slow 
growth  influences  tangential  cleavage,  narrow-ringed  oak  breaks  out  and 
splits  less  regularly  even  in  a  radial  direction  ;  in  conifers,  however,  this 
difference  scarcely  exists.  Weight  of  wood  affects  the  cleavage  but  little ;  in 
heavy  wood  the  entrance  of  the  axe,  to  be  sure,  is  resisted  with  more  force, 
but  the  greater  rigidity  of  the  wood,  on  the  other  hand,  counterbalances  this 
resistance.  Irregularities  in  the  course  of  the  fibres,  whether  spiral  growth, 
cross-grain,  or  in  form  of  knots,  all  aid  in  resisting  cleavage.  Knotty  sticks 
.are  split  more  easily  from  the  upper  end,  since  the  cleft  then  runs  around  the 
knots  (see  Fig.  95).  Moisture  softens  the  wood  and  reduces  lateral  adhe- 
sion, and  therefore  wood  splits  more  easily  when  green  than  when  dry. 

205.  Flexibility.* — Pine    is  brittle,  hickory  is    flexible  ;    the    former 
breaks,  the  latter  bends.     Being  the  opposite  of  stiffness,  want  of  stiffness 
would  seem  to  indicate  flexibility.    This,  however,  is  only  partly  true;  hick- 
ory and  ash  are  stiff  and  yet  among  the  most  flexible  of  woods.     Their 
small  dimensions  cause  shavings  and  thin  strands  of  most  woods  to  appear 
pliable.     For  this  reason  the  pliable,  twisted  wicker-willow  is  not  a  fair 
measure  of  the   flexibility  of    the  wood  of   this  species.     Generally  hard 
woods  are  more  flexible   than  conifers,  wood  of  the  butt  surpassing  in  this 
respect  that  of  the  main  part  of  the  stem,  the  latter  being  usually  superior 
to  that  of  the  limbs.     Moisture  softens  wood  and  thereby  increases  its  flexi- 
bility.    Knots  and  cross-grain  diminish  flexibility,  but  the  irregular  struc- 
ture of  elm,  ash,  etc.  (particularly  the  arrangement  of  bodies  of  extremely 
firm  fibres,  like  so   many  strands,  among  the  softer  tissue,  as  well  as  the 
interlacement  of  fibres  due  to  post-cambial  growth),  favorably  influences' 
the  flexibility  of  these  woods. 

206.  Toughness,  f — So  far  the  load  by  which  the  exhibition  of  the  vari- 
ous kinds  of  strength  in  compression,  tension,  cross-bending,  etc.,  was  pro- 

*  The  writer  here  uses  "  flexibility  "  as  Rankine  uses  "toughness,"  that  is,  the  ability 
to  withstand  great  deformation  before  rupture.  Flexibility,  as  the  opposite  of  stiff- 
ness or  rigidity,  would  signify  the  readiness  to  deflect  under  a  given  load,  which  is 
mathematically  shown  by  a  small  modulus  of  elasticity. — J.  13.  J. 

f  The  writer  here  uses  toughness  as  indicating  resilience,  when  this  term  is  made  to 
upply  to  the  whole  period  of  deformation  and  not  simply  to  the  elastic  field.— J.  B.  J. 


TIMBER.  245 

duced  has  always  been  assumed  as  applied  slowly  and  gradually.  When  a 
wagon  goes  lumbering  along  a  cobble  pavement,  the  load  on  the  spokes  is 
not  thus  applied.  Every  stone  deals  the  wheel  a  blow,  and  a  mile's- 
journey  means  many  thousand  blows  to  every  wheel-rim  and  spoke.  In 
chopping,  the  axe-handle  is  jarred,  and  a  handle  made  of  pine  wood,  which 
shears  easily  along  the  fibre,  would  soon  be  shattered  to  pieces.  Loads 
thus  applied  are  "  shocks,"  and  resistance  to  this  form  of  loading  requires 
a  combination  of  various  kinds  of  strength  possessed  only  by  "  tough  " 
woods.  Toughness  is  a  familiar  word  to  woodworkers,  and  yet  is  rarely 
defined.  Tough  wood  must  be  both  strong  and  pliable.  Thus  a  willow  is 
not  tough  when  dry;  it  is  weak  and  brittle,  and  requires,  notwithstanding 
its  small  lateral  dimensions,  to  be  moistened  and  twisted  or  sheared  inta 
still  smaller  strands  so  that  its  fibres  are  subjected  almost  exclusively  to  ten- 
sion if  great  deflection  and  great  strength  are  to  be  combined  (handles  of 
wicker  baskets).  Hickory  is  both  strong  and  pliable  ;  in  the  dimensions 
of  a  willow  twig  it  can  be  used  almost  like  a  rope.  The  term  "  tough," 
therefore,  is  properly  applied  to  woods  like  hickory  and  elm,  and  improp- 
erly to  willow. 

Judging  from  the  behavior  of  elm  and  hickory,  wood  may  be  pro- 
nounced "  tough  "  if  it  offers  great  resistance  to— 

(1)  Longitudinal  shearing  over  1000  pounds  per  square  inch, 

(2)  Tension  over  1G,000  pounds  per  square  inch, 

and  permits,  when  tested  dry,  of  an  aggregate  combined  distortion  in. 
compression  and  tension  amounting  to  not  less  than  3  per  cent. 

For  instance,  of  a  piece  of  dry  hickory  (//.  alba)  we  may  expect — 

Strength  in  shearing pounds     1,200 

Strength  in  tension do.      25,000 

Distortion  in  tension percent       2.03 

Distortion  in  compression do.      *     1.55 

Total  distortion do.  3.58 

207.  Practical  Conclusions. — From  the  foregoing  considerations  a  few 
valuable  facts,  mostly  familiar  to  the  thoughtful  woodworker,  may  be 
deduced 

In  framing,  where  light  and  stiff  timber  is  wanted,  the  conifers  excel; 
where  heavy  but  steady  loads  are  to  be  supported,  the  heavier  conifers,  hard 
pine,  spruce,  Douglas  spruce,  etc.,  answer  as  well  as  hard  woods,  which  are 
costlier  and  heavier  for  the  same  amount  of  stiffness.  On  the  other  hand, 
if  small  dimensions  must  be  used,  and  especially  if  moving  loads  are  to  be 
sustained,  hard  woods  are  safest,  and  in  all  cases  where  the  load  is  applied 
in  form  of  "shocks"  or  jars,  only  the  tougher  hard  woods  should  be  em- 
ployed. The  heavier  wood  surpasses  the  lighter  of  the  same  species  in  all 
kinds  of  strength,  so  that  the  weight  of  dry  wood  and  the  structural  fea- 


246  THE  MATERIALS  OF  CONSTRUCTION. 

tures  indicative  of  weight  may  be  used  as  safe  signs  in  selecting  timber  for 
strength. 

In  shaping  wood  it  is  better,  though  more  wasteful,  to  split  than  to  saw, 
because  it  insures  straight  grain  and  enables  a  more  perfect  seasoning. 

For  sawed  stock  the  method  of  "rift"  or  "quarter"  sawing,  which  has 
so  rapidly  gained  favor  during  the  last  decade,  deserves  every  encourage- 
ment. It  permits  of  better  selection  and  of  more  advantageous  disposition 
of  the  wood;  rift-sawed  lumber  is  stronger,  wears  better,  seasons  well,  and 
is  least  subject  to  "working"  or  warping. 

All  hardwood  material  which  checks  or  warps  badly  during  seasoning 
should  be  reduced  to  the  smallest  practicable  size  before  drying,  to  avoid 
the  injuries  involved  in  this  process;  and  wood  once  seasoned  should  never 
again  be  exposed  to  the  weather,  since  all  injuries  due  to  seasoning  are 
thereby  aggravated.  Seasoning  increases  the  strength  of  wood  in  every 
respect,  and  it  is  therefore  of  great  importance  to  protect  wooden  struc- 
tures bearing  heavy  weights  against  moisture. 

Knots,  like  cross-grain  and  other  defects,  reduce  the  strength  of  timber. 
Where  choice  exists,  the  knotty  side  of  the  joist  should  be  placed  upper- 
most, i.e.,  should  be  used  in  compression. 

Season-checks  in  timber  are  always  a  source  of  weakness;  they  are  more 
injurious  on  the  vertical  than  on  the  horizontal  faces  of  a  stringer  or  joist, 
and  their  effect  continues  even  when  they  have  closed  up,  as  many  do,  and 
are  no  longer  visible. 

Rafted  timber,  kiln-dried  or  steamed  lumber  are,  as  far  as  our  present 
knowledge  extends,  as  strong  as  other  kinds;  and  wherever  any  of  these  pro- 
cesses aids  in  a  more  uniform  or  perfect  seasoning,  it  increases  the  strength 
of  the  material. 

Pine  ''bled"  for  turpentine  is  as  strong  as  "unbled." 

Time  of  felling,  whether  season  of  the  year  or  phase  of  the  moon,  does 
not  influence  strength,  except  that  summer-felled  hard  wood  rarely  seasons 
as  perfectly  as  that  felled  in  the  fall,  and  to  this  extent  an  indirect  influence 
may  be  observed,  as  well  as  by  the  fact  that  fungi  and  insects  have  a  better 
opportunity  for  developing. 

Warm  countries  and  sunny  exposures  generally  produce  heavier  and 
stronger  timber,  and  conditions  favorable  to  the  growth  of  the  species  also 
improve  its  quality.  But  exceptions  occur;  neither  fast  nor  slow  growth  is 
an  infallible  sign -of  strong  wood,  and  it  is  the  character  of  the  annual  ring, 
rather  than  its  width,  and  particularly  the  proportion  of  summer  wood, 
which  determines  the  quality  of  the  material. 

CHEMICAL   PROPERTIES   AND   TECHNOLOGICAL   PRODUCTS   OF  WOOD. 

208.  Chemical  Composition. — Wood  dried  at  300°  F.  is  composed  of  over 
99  per  cent  of  organic  and  less  than  1  per  cent  of  inorganic  matter;  the 
latter  remains  as  ashes  when  wood  is  burned. 


TIMBER.  247 

Wood  consists  of  a  skeleton  of  cellulose,  permeate^  by  a  mixture  of 
other  organic  substances,  collectively  designated  by  the  word  lignin,  and 
particles  of  mineral  matter  or  ashes. 

Cellulose  is  the  common  substance  of  which  plant-cells  form  their  cases 

or  walls;  in  flax,  the  entire  fibre  is  almost  pure  cellulose,  but  the  amount 

'  of  cellulose  obtained  from  wood,  by  the  common  processes,  rarely  exceeds 

'  one  half  of   its  dry  weight.     Cellulose   is    identical  in   composition  with 

starch,  but  unlike  the  latter  it  resists  alcoholic  fermentation,  though  the 

plants  themselves,  as  well  as  decay-producing  fungi,  are  able  to  reconvert 

it  into  starch,  from  which  it  seems  originally  derived,  and  also  to  change  it 

into  various  forms  of  sugar.*     Lignin  is  as  yet  a  chemical  puzzle.     The 

|  substances  forming  it  are  carbohydrates  like  cellulose  itself,  but  of  slightly 

j  different  proportions  and  distinguished  by  greater  solubility  in  acids,  and 

by  other  chemical  properties. 

In  100  pounds  of  wood  (dried  at  300°  F.)  and  of  cellulose  the  following 
proportions  are  found : 

Wood,         Cellulose, 
Pounds.        Pounds. 

Carbon 49  44.4 

Hydrogen G  C.  1 

Oxygen 44  49.3 

This  composition  of  wood  is  fairly  uniform  for  different  species. 

At  ordinary  temperatures  wood  is  a  very  stable  compound;  both  in  air 
and  under  water  it  remains  the  same  for  centuries,  and  only  when  living 
organisms  attack  it  with  their  strono"  solvents  and  convertants  do  change 
and  decay  set  in. 

209.  Wood  as  a  Fuel.— Heated  to  300°  F.  wood  gives  off  only  water, 
though  some  slight  chemical  changes  are  noticeable  even  at  this  tempera- 
ture. If  the  heat  is  increased,  gases  of  pungent  odor  and  taste  are  evolved; 
and  if  the  temperature  is  sufficiently  raised,  the  gases  may  be  ignited,  form- 
ling  the  flame  of  the  fire,  while  the  remaining  solid  part  glows  like  an  ignited 
: charcoal,  giving  much  heat,  but  no  flame.  The  amount  of  heat  produced 
by  wood  varies.  If  first  dried  at  300°  F.,  100  pounds  of  poplar  wood  should 
give  as  much  heat  as  100  pounds  of  hickory.  In  the  natural  state,  however, 
this  is  not  the  case. 

The  beneficial  effect  of  thorough  seasoning  for  firewood  appears  from 
the  following  consideration : 

One  hundred  pounds  of  wood  as  sold  in  the  wood-yards  contains  in  round 
numbers  25  pounds  of  water,  74  pounds  of  wood,  and  1  pound  of  ashes. 

The  74  pounds  of  wood  are  composed  of  37  pounds  of  carbon,  4.4  pounds 

of  hydrogen,  and  32  pounds  of  oxygen. 

. — f 

*  Chemists  have  succeeded  in  producing  reconversion  into  grape-sugar;  and  though 
the  methods  thus  far  employed  are  expensive,  it  is  to  be  expected  that  in  the  near  future 
Nvood  will  become  the  principal  source  of  both  vinegar  and  alcohol. 


248  THE  MATERIALS  OF  CONSTRUCTION. 

In  burning  (which  is  a  process  of  oxidation)  4  pounds  of  hydrogen  are 
already  combined  with  32  pounds  of  oxygen,  and  there  are  only  the  37  pounds 
of  carbon  and  0.4  pound  of  hydrogen  available  in  heat-production.  Thus 
only  about  one  half  the  weight  of  the  wood-substance  itself  is  heat-produc- 
ing, while  every  pound  of  water  combined  in  the  wood  requires  about  600 
units  of  heat  to  evaporate  it,  and  thus  diminishes  the  value  of  the  wood  as 
fuel.  Hence  under  the  most  favorable  circumstances  100  pounds  of  green 
wood  (50  percent  moisture)  furnishes  about  270,000  units  *  of  heat;  100 
pounds  of  half-dry  (30  per  cent  moisture)  about  410,000  units;  100  pounds 
of  air-dry  (20  per  cent  moisture)  about  500,000  units;  100  pounds  of  air- 
dry  (10  per  cent  moisture)  about  580,000  units;  100  pounds  of  kiln-dry  (£ 
per  cent  moisture)  about  630,000  units. 

In  the  ordinary  stove  or  other  small  apparatus  the  evil  effect  of  moisture 
in  the  wood  is  very  much  increased,  since  combustion  is  materially  interfered 
with. 

One  hundred  pounds  of  ordinary  charcoal  furnishes  1,  200,000  units  of 
heat,  but  the  same  quantity  of  charcoal  produced  at  a  temperature  of  2000° 
F.  furnishes  140,000  units  of  heat. 

Conifers  and  the  lighter  hard  woods  produce  more  flame,  while  the  heavy 
hard  woods  furnish  a  good  bed  of  live  coal  and  exceed  the  former  by  25  to 
30  per  cent  in  production  of  heat  with  ordinary  appliances. 

210.  Charcoal. — Heated  in  a  closed  chamber  or  covered  with  earth,  as  in 
charcoal-pits,  the  wood  is  prevented  from  burning  and  a  variety  of  changes 
occur,  depending  on  the  rate  of  heating.     If  the  temperature  is  raised  grad-J 
ually  so  that  the  wood  is  heated  several  hours  before  a  temperature  of  600° 
F.  is  reached,  the  process  is  called  dry  distillation.    In  this  process  the  wood 
is  destroyed.     It  forms  at  first  "red"  or  "brown"  coal,  still  resembling 
wood,  and  finally  charcoal  proper.     This  coal  is  darker,  heavier,  conducts 
heat  and  electricity  better,  requires  a  greater  heat  to  ignite,  and  produces 
more  heat  per  pound  in  burning  the  higher  the  temperature  under  which  iti 
is  formed. 

One  hundred  pounds  of  wood  (dried  at  300°  F.)  leaves  only  about  3C 
pounds  of  charcoal.     In  common  practice  much  less  charcoal  (18  to  20  peil 
cent)  is  produced.     In  this  change  from  wood  to  coal  the  volume  is  dimin- 
ished by  one  half,  so  that  a  cord  of  wood  which  contains  about  100  cubic ; 
feet  of  wood  solid  would  be  converted  into  50  cubic  feet  at  best. 

211.  Products  of  Wood-distillation. — Of  the  70  pounds  of  gaseous  prod 
nets  which  100  pounds  of  wood  lose,  during  coaling,  in  being  heated  up  t<| 
700°  F.,  about  63  pounds  become  volatile  before  the  temperature  of  550°  F 
is  reached. 

If  condensed  in  a  cooler,  about  three  fourths  of  the  63  pounds  of  vol 


*  A  unit  of  heat  in  this  case  is  the  amount  of  heat  which  raises  the  temperature  c 
1  pound  of  water  1°  F. 


TIMBER.  249 

atile  matter  first  evolved  is  found  to  be  wood -vinegar,  from  which  about 
4  pounds  of  pure  acetic  acid,  the  only  source  of  perfectly  pure  vinegar,  is 
obtained.  Besides  acetic  acid,  the  liquid  contains  wood-spirits  and  a  quan- 
tity of  various  allied  substances. 

After  the  first  stage  of  dry  distillation,  a  large  part  of  the  products  devel- 
oped cannot  be  liquefied  in  the  ordinary  cooler.  They  are  gases  like  the 
illuminating-gas,  mostly  belonging  to  the  marsh-gas  series;  they  lack  oxy- 
gen and  thus  show  ftiat  the  available  oxygen  has  been  nearly  exhausted  in 
the  preceding  part  of  the  process.  Products  of  the  latter  stages  are  tars 
and  heavy  oils,  volatile  only  at  high  temperatures.  Here  also  belong  the 
substances,  known  collectively  as  wood-creosote,  employed  as  antiseptics  in 
wood -impregnation. 

212.  Cellulose. — Warmed  in  dilute  nitric  acid  with  a  little  chlorate  of 
potash,  the  cells  of  a  piece  of  wood  may  be  separated.    Each  cell  remains 
intact,  but  its  wall  is  reduced  in  thickness  and  material ;  the  lignin  substances 
being  dissolved  out,   only   the   cellulose  is  left.     In   commercial-cellulose 
manufacture,  soda,  sulphates,  and  of  late  chiefly  sulphites  are  substituted 
for  the  nitric  acid.     The  wood  is  chipped,  boiled  in  the  respective  solution 
under  high  pressures,  the  residue  is  washed,  and  the  remaining  cellulose 
bleached  and  ready  for  use.     As  a  matter  of  economy  the  residual  liquid  is 
evaporated  and  the  soda  used  over  again. 

213.  Resin,  Turpentine,  and   Lampblack. — When   resinous   wood,   "fat 
pine,"  "lightwood,"  such  as  the  knots  and  stumps  of  long-leaf,  pitch,  and 
other  pines,  is  heated  in  a  kiln  or  retort,  the  resins  ooze  out,  are  collected, 
and  in  distillation  with  steam  yield  turpentine  and  resin.     The  resins  and 
their  components  vary  with  the  species;  the  balsam  of  fir  is  limpid,  its  tur- 
pentine remains  clear  on  exposure;  the  resin  of  pines  is  very  viscid,  their 
turpentines  readily  oxidize  and  darken  when  brought  in  contact  with  air. 
Resins  are  gathered  more  commonly  either  from  cracks,  such  as  "  wind  "  and 
"ring  shakes,"  as  in  the  case  of  larch  and  fir  (Venetian  turpentine),  or  else 
from  wounds  made  especially  for  this  purpose,  as  in  the  case  of  naval  stores 
gathered  from  pines.    This  latter  process  is  known  as  "  bleeding,"  "  tapping," 
or  "  orcharding,"  and  is  at  present  the  principal  method  of  obtaining  tur- 
pentines 'and  resins. 

On  burning  resinous  wood,  wood-tar,  etc.,  in  a  smouldering  fire,  soot  is 
deposited  on  the  walls  and  partitions  of  the  specially  constructed  soot-pit. 
It  is  then  collected,  but  must  be  freed  of  various  products  of  dry  distilla- 
tion, by  carefully  heating  to  red  heat,  before  it  becomes  the  lampblack  used 
in  printer's  ink  and  otherwise  much  employed  in  the  arts. 

214.  Tannin. — Many  kinds  of  wood  and  the  bark  of  most  trees  contain 
tannin.     To  serve  in  tanning  the  bark  must  contain  at  least  3  per  cent  of 
tannin;  the  kind's  mostly  used  vary  from  5  to  15  per  cent,  and  even  the  best 
probably  never  furnish  over  20  per  cent  in  the  average.     The  use  of  tan- 
bark  involves  many  disadvantages.     It  is  difficult  to  dry  and  preserve,  very 


250  THK  MATERIALS  OF  CONSTRUCTION. 

liable  to  mould,  it  is  bulky  and  therefore  expensive  to  ship  and  store,  and 
very  variable  in  the  amount  of  tannin  which  it  contains. 

To  avoid  these  difficulties  the  tannic  compounds  are,  in  recent  times, 
leached  out  of  the  finely  ground  bark  and  wood,  condensed  by  evaporation, 
and  shipped  as  extracts  containing  20  to  40  per  cent  of  tannin. 

The  manufacture  of  pulp,  and  the  production  of  fibre  capable  of  being 
spun  and  woven,  are  also  technological  uses  of  wood  Which  rely  partly  upon 
chemical  reactions. 

DURABILITY  AND  DECAY  OF  WOOD. 

215.  All  Decay  Produced  by  a  Fungus-growth. — All  wood  is  equally 
durable  under  certain  conditions.  Kept  dry  or  submerged,  it  lasts  indefi- 
nitely. Pieces  of  pine  have  been  unearthed  in  Illinois  which  have  lain 
buried  60  or  more  feet  deep  for  many  centuries.  Deposits  of  sound  logs  of 
oak,  buried  for  unknown  ages,  have  been  unearthed  in  Bavaria;  parts  of  the 
piles  of  the  lake-dwellers,  driven  more  than  two  thousand  years  ago,  are 
still  intact. 

On  the  radial  section  of  a  piece  of  pine  timber,  with  one  of  the  shelf -like 
fungus-growths,  as  shown  in  Fig.  115,  both  bark  and  wood  are  seen  to  be 
affected.  A  small  particle  of  the  half-decayed  wood  presents  pictures  like 
that  of  Fig.  116.  Slender,  branching  threads  are  seen  to  attach  themselves 
closely  to  the  walls  of  the  cells,  and  to  pierce  these  in  all  directions.  Thus 
these  little  threads  of  fungus  mycelium  soon  form  a  perfect  network  in  the 
wood,  and  as  they  increase  in  number  they  dissolve  the  walls,  and  convert 
the  wood-substance  and  cell-contents  into  sugar-like  food  for  their  own  con- 
sumption. In  some  cases  it  is  the  woody  cell-wall  alone  that  is  attacked. 
In  other  cases  they  confine  themselves  to  eating  up  the  starch  found  in  the 
cells,  as  shown  in  Fig.  117,  and  merely  leave  a  stain  (bluing  of  lumber).  In 
all  cases  of  decay  we  find  the  vegetative  bodies,  these  slender  threads  of 
fungi,  responsible  for  the  mischief.  These  fine  threads  are  the  vegetative 
body  of  the  fungus;  the  little  shelf  is  its  frniting-body,  on  which  it  pro- 
duces myriads  of  little  spores  (the  seeds  of  fungi).  Some  fungi  attack  only 
conifers,  others  hard  woods  ;  many  are*confined  to  one  species  of  tree,  and 
perhaps  no  one  attacks  all  kinds  of  wood.  One  kind  produces  "  red  rot," 
others  "  bluing."  In  one  case  the  decayed  tracts  are  tabular,  and  in  the 
direction  of  the  fibres  the  wood  is  "  peggy."  In  other  cases  no  particular 
shapes  are  discernible. 

Cutting  off  a  disk  of  loblolly  pine,  washing  it,  and  then  laying  it  in  a 
clean,  shady  place  in  the  sawmill,  its  sap  wood  will  be  foumd  stained  in  a 
few  days.  Nor  is  this  mischief  confined  to  the  surface;  it  penetrates  the 
sapwood  of  the  entire  disk.  From  this  it  appears  that  the  spores  must  have 
been  in  the  air  about  the  mill,  and  also  that  their  germination  and  the 
growth  of  the  threads  or  mycelium  are  exceedingly  rapid.  (Watching  the 


TIMBER. 


progress  of  mould  on  a  piece  of  bread  teaches  the  same  thing.)  Placing  a 
fresh  piece  of  sapwood  on  ice,  another  into  a  dry  kiln,  and  soaking  a  few 
others  in  solutions  of  corrosive  sublimate  (mercuric  chloride)  and  other  sim- 
ilar salts,  we  learn  that  the  fungus-growth  is  retarded  by  cold,  prevented 
and  killed  by  temperatures  over  150°  F.,  and  that  salts  of  mercury,  etc., 
have  the  same  effect.  The  fact  that  seasoned  pieces  if  exposed  are  not  so 


FIG.  115. 

PIG.  115.— "Shelf"  Fungus  on  the  Stem  of  a  Pine.  (Hartig.)  a,  sound  wood;  b, 
resinous  "light"  wood;  c,  partly  decayed  wood  or  punk;  d,  layer  of  living  spore- 
tubes;  e,  old  flllcd-up  spore-tubes;  /,  fluted  upper  surface  of  the  fruiting-body  of 
the  fungus,  which  gets  its  food  through  a  great  number  of  fine  threads  (the  my- 
celium), its  vegetative  tissue  penetrating  the  wood  and  causing  its  decay. 

FIG.  116.— Fungus-threads  iu  Pine  Wood.  (Hartig.)  a,  cell-wall  of  the  wood-fibres ; 
b,  bordered  pits  of  these  fibres;  c,  thread  of  mycelium  of  the  fungus;  d,  holes  in 
the  cell-walls  made  by  the  fungus-lhreads,  which  gradually  dissolve  the  walls  as 
shown  at  e,  and  thus  break  down  the  wood-structure. 

readily  attacked  by  fungi  shows  that  the  moisture  in  air-dried  wood  is  insuf- 
ficient for  fungus-growth. 

From  this  it  appears  that  warmth,  preferably  between  60°  and  100°  F., 
combined  with  abundance  of  moisture  (but  not  immersion),  is  the  most 
important  condition  favoring  decay,  and  that  the  defence  lies  in  the  proper 
regulation  or  avoidance  of  these  conditions,  or  else  in  the  use  of  poisonous 
salts,  which  prevent  the  propagation  of  fungi. 


252 


THE  MATERIALS  OF  CONSTRUCTION. 


It  is  also  apparent,  therefore,  why  wood  decays  faster  in  Alabama  than 
in  Wisconsin,  faster  in  the  swamps  than  on  the  plains,  and  why  the  presence 
of  large  quantities  of  decaying  wood  about  the  yard,  constantly  producing 
fresh  supplies  of  spores,  stimulates  decay.  Covering  with  tar  or  impregnat- 

ing  with  creosote,  salts  of  mercury,  cop- 
per,  etc.,  enables  even  sapwood  to  last 
under  the  most  trying  conditions.  Con- 
tact with  the  ground  assures  most  favor- 
able moisture  conditions  for  fungus- 
growth,  and  the  higher  temperatures 
near  the  surface  of  the  ground,  together 
with  the  ever-present  supply  of  spores, 
cause  rot  in  a  post  to  start  at  the  sur- 
face more  readily  than  30  inches  below. 
216.  Prevention  of  Decay. — The 
use  of  means  to  prevent  decay  is  there- 
fore desirable  where  timber  is  placed  in 
positions  favorable  to  fungus-growth, 
as  in  railway  ties ;  and  all  joists  and  tim- 
ber in  contact  with  damp  brick  walls,  as 
also  all  building  material  whose  perfect 
seasoning  is  prevented  by  the  absence 
of  proper  circulation  of  air,  should  be 
specially  protected.  In  the  former  cases 
it  is  economy  to  apply  preservative  proc- 
esses; in  the  latter  a  sanitary  necessity. 
Wood  covered  with  paint,  etc.,  before 
it  is  perfectly  seasoned  falls  a  prey  to 
"dry-rot  "  ;  the  fungus  finds  abundance 
of  moisture,  and  the  protection  intended 
FHJ.  117.— Cells  of  Maple-wood  attacked  for  the  wood  protects  its  enemy,  the 
by  Fungus-threads  (Neciria  cinna-  fungus.  Since  charcoal  resists  the  sol- 
bnrina  Mayer).  Section  of  three  vents  of  fungi,  charring  the  outer  parts 
.wood-fibres  showing  the  threads  of  the  of  pogts  makes?  jf  wen  done,  namely,  so 
fungus  branching  in  their  cavities  and  ^  uot  t()  checks  .^  ^  ^^ 

consuming  the  starch  stored  in  these 

cells,     a,  interior  or  cavity  of  cells  ;  b,  of  tlie  wood>  a  ™?J  fine  protection, 
threads  of  the  fungus ;  c,  partly  de-         Under  ordinary  circumstances,  only 
stroyed  starch-grains;    d,  dead  por-  the  second  great  factor  of  decay,  i.e., 
tions  of    the  fungus-thread  together  the   moisture   condition,    can   be   con- 


witli  debris  ;  e,  holes  bored  by  the 
fungus  through  the  cell-walls  ;  S, 
starch-grains  just  being  attacked. 


trolled. 


Perfect  seasoning,  preferably  kiln- 
drying,  before  using,  and  protection 
against  the  entrance  of  moisture  by  tar,  paints,  and  other  covers,  when  put 
in  place,  prolong  the  life  of  wooden  structures.  Where  such  a  covering  is 
too  expensive,  good  ventilation  at  least  is  necessary.  Contact-surfaces, 


TIMBER.  253 

where  timber  rests  on  timber  or  brick,  should  in  all  cases  be  especially  pro- 
tected. 

Different  species  differ  in  their  resistance  to  decay.  Cedar  is  more 
durable  than  pine,  and  oak  better  than  beech;  but  in  most  cases  the  condi- 
tions of  warmth  and  moisture  in  particular  locations  have  so  much  to  do 
with  durability  that  often  an  oak  post  outlasts  one  of  cedar,  even  in  the  same 
line  of  fence,  and  predictions  of  durability  become  mere  guesswork. 

Containing  more  ready-made  food,  and  in  forms  acceptable  to  a  great 
number  of  different  kinds  of  fungi,  the  sapwood  is  more  subject  to  decay 
than  the  heartwood,  doubly  so  where  the  latter  is  protected  by  resinous  sub- 
stances, as  in  pine  and  cedar.  Several  months  of  immersion  improves  the 
durability  of  sapwood,  but  only  impregnation  with  preservative  salts  seems 
to  render  it  perfectly  secure.  Once  attacked  by  fungi,  wood  becomes  pre- 
disposed to  further  decay. 

Wood  cut  in  the  fall  is  more  durable  than  that  cut  in  summer,  only 
because  the  low  temperature  of  the  winter  season  prevents  the  attack  of  the 
fungi,  and  the  wood  is  thus  given  a  fair  chance  to  dry.  Usually  summer- 
felled  wood,  on  account  of  prevalent  high  temperature  and  exposure  to  sun, 
checks  more  than  winter-felled  wood ;  and  since  all  season-checks  favor  the 
entrance  of  both  moisture  and  fungus,  they  facilitate  destruction.  Where 
summer-felled  wood  is  worked  up  at  once  and  protected  by  kiln-drying,  no 
difference  exists.  (The  phases  of  the  moon  have  no  influence  whatever  on 
durability!) 

In  sawing  timber  much  of  the  wood  is  bastard-cut;  at  these  places  water 
enters  much  more  readily,  and  for  this  reason  split  and  hewn  timber  and 
ties  generally  resist  decay  perhaps  better  than  if  sawed. 

The  attacks  of  beetles,  as  well  as  those  of  the  shipworm,  cannot  here  be 
considered ;  like  chisel  or  saw  they  are  mechanical  injuries  against  which 
none  of  our  woods  are  proof,  except  by  impregnation  of  creosote  or  other 
chemical. 

RANGE    OF    DURABILITY    IN    RAILROAD-TIES. 

Years. 

Redwood 12 

Cypress  and  red  cedar 10 

Tamarack 7  to  8 

Long-leaf  pine 6 

Hemlock 4  to  6 

Spruce 5 


Years. 


White  oak  and  chestnut  oak. 
Chestnut... 


Black  locust 10 

Cherry,  black  walnut,  locust 7 

Elm..,  ,;  6  to  V 


Red  and  black  oaks 4  to  5 

Ash,  beech,  maple 4 

The  durability  of  wood  exposed  to  the  changes  of  the  weather  and 
where  painting,  after  thorough  seasoning,  is  impracticable,  is  increased  by 
impregnating  it  with  various  salts  or  other  chemicals  which  prevent  the 
fungus  from  feeding  on  the  wood.  The  wood  is  first  steamed,  to  open  the 
pores  and  remove  the  hardened  surface  coating  of  sap  and  dirt,  and  a  liquid 
solution  of  the  preservative  material  is  then  injected  with  the  assistance  of 
heat  and  pressure. 


254  TEE  MATERIALS  OF  CONSTRUCTION. 

The  most  efficient  fluids  used  on  a  large  scale  are  bichloride  of  zinc  and 
creosote,  or  both  combined.  The  "  life  "  of  railroad-ties  is  thereby  increased 
to  twice  and  three  times  its  natural  duration. 

HOW   TO   DISTINGUISH    THE   DIFFERENT   KINDS   OF  WOOD.*, 

217.  An  Examination  of  the  Structure  Essential  to  Identification. — The 

carpenter  or  other  artisan  who  handles  different  woods  becomes  familiar  with 
those  he  employs  frequently,  and  learns  to  distinguish  them  through  this 
familiarity,  without  usually  being  able  to  state  the  characteristic  differences. 
If  a  wood  comes  before  him  with  which  he  is  not  familiar,  he  has,  of  course, 
no  means  of  determining  what  it  is,  and  it  is  possible  to  select  pieces  even  of 
those  with  which  he  is  well  acquainted,  different  in  appearance  from  the 
average,  that  will  make  him  doubtful  as  to  their  identification.  Further- 
more, he  may  distinguish  between  hard  and  soft  pines,  between  oak  and 
ash,  or  between  maple  and  birch,  which  are  characteristically  different;  but 
when  it  comes  to  distinguishing  between  the  several  species  of  pine  or  oak 
or  ash  or  birch,  the  absence  of  readily  recognizable  characteristics  is  such 
that  but  few  practitioners  can  be  relied  upon  to  do  it.  Hence  in  the 
markets  we  find  many  species  mixed  and  sold  indiscriminately. 

To  identify  the  different  woods  it  is  necessary  to  have  a  knowledge  of 
the  definite,  invariable  differences  in  their  structure,  besides  that  of  the 
often  variable  differences  in  their  appearance.  These  structural  differences 
may  either  be  readily  visible  to  the  naked  eye  or  with  a  magnifier,  or  they 
may  require  a  microsocpical  examination.  In  some  cases  such  an  examina- 
tion cannot  be  dispensed  with  if  we  would  make  absolutely  sure.  There  are 
instances,  as  in  the  pines,  where  even  our  knowledge  of  the  minute  anatom- 
ical structure  is  not  yet  sufficient  to  make  a  sure  identification. 

218.  A  Structural  Key  to  Species. — In  the  following  key  an  attempt  has 
been  made — the  first,  so  far  as  we  know,  in  English  literature — to  give  a 
synoptical  view  of  the  distinctive  features  of  the  commoner  woods  of  the 
United  States  which  are  found  in  the  markets  or  are  used  in  the  arts.     It 
will  be  observed  that  the  distinction  has  been  carried  in  most  instances  no 
further  than  to  genera  or  classes  of  wood's,  since  the  distinction  of  species 
can  hardly  be  accomplished  without  elaborate  microscopic  study,  and  also 
that,  as  far  as  possible,  reliance  has  been  placed  only  on  such  characteristics 
as  can  be  distinguished  with  the  naked  eye  or  a  simple  magnify  ing-glass,  in 
order  to  make  the  key  useful  to  the  largest  number.     Recourse  has  also- 
been  taken  for  the  same  reason  to  the  less  reliable  and  more  variable  general 
external  appearance,  color,  taste,  smell,  weight,  etc. 

The  user  of  the  key  must,  however,  realize  that  external  appearance, 
such,  for  example,  as  color,  is  not  only  very  variable,  but  also  very  difficult 
to  describe,  individual  observers  differing  especially  in  seeing  and  describing 

*  The  matter  in  the  remainder  of  this  chapter  is  mostly  the  joint  product  of  Dr. 
B.  E.  Fernow  and  Mr.  Filibert  Roth. 


TIMBER.  255 

shades  of  color.  The  same  is  true  of  statements  of  size  when  relative  and 
not  accurately  measured,  while  weight  and  hardness  can  perhaps  be  more 
readily  approximated.  Whether  any  feature  is  distinctly  or  only  indistinctly 
seen  will  also  depend  somewhat  on  individual  eyesight,  opinion,  or  practice. 
In  some  cases  the  resemblance  of  different  species  is  so  close  that  only  one 
other  expedient  will  make  distinction  possible,  namely,  a  knowledge  of  the 
region  from  which  the  wood  has  come.  We  know,  for  instance,  that  no 
long-leaf  pine  grows  in  Missouri  or  Arkansas,  and  that  no  white  pine  can 
come  from  Alabama,  and  we  can  separate  the  white  cedar,  giant  arbor  vit^e 
of  the  West  and  the  arbor  \itse  of  the  Northeast  only  by  the  difference  of 
the  locality  from  which  the  specimen  comes.  With  all  these  limitations 
properly  appreciated,  the  key  will  be  found  helpful  toward  greater  familiar- 
ity with  the  woods  which  are  more  commonly  met  with. 

219.  Characteristic  Structural  Features. — The  features  which  have  been 
utilized  in  the  key  and  with  which  (their  names  as  well  as  their  appearance), 
therefore,  the  reader  must  familiarize  himself  before  attempting  to  use 
the  key,  are  mostly  described  as  they  appear  in  cross-section.  They  are: 

(1)  Sapwood  and  heart  wood  (see  Art.  180),  the  former  being  the  wood 

from  the  outer,  and  the  latter  from  the  inner,  part  of  the  tree.     In  some 

•- A--  — 


B C 


FIG.  118. — " Nou-porous"  Woods.  A,  fir;  B,  "  Lmrd  "  pine;  C,  soft  pine,  ar,  annual 
ring,  o.  e.,  outer  edge  of  ring;  i.  e.,  inner  edge  of  ring;  s.  w.,  summer  wood;  sp.  w.t 
spring  wood;  rd,  resin-ducts. 

cases  they  differ  only  in  shade,  and  in  others  in  kind  of  color,  the  heartwood 
exhibiting  either  a  darker  shade  or  a,  pronounced  color.  Since  one  cannot 
always  have  the  two  together,  or  be  certain  whether  he  has  sapwood  or 
heartwood,  reliance  upon  this  feature  is,  to  be  sure,  unsatisfactory,  yet 
sometimes  it  is  the  only  general  characteristic  that  can  be  relied  upon.  If 
farther  assurance  is  desired,  microscopic  structure  must  be  examined;  in 
such  cases  reference  has  been  made  to  the  presence  or  absence  of  tracheids  in 
pith-rays  and  the  structure  of  their  Avails,  especially  projections  and  spirals. 

(2)  Annual  rings,  their  formation  having  been  described  in  Art.  181. 
(See  also  Figs.  118,  120.)     They  are  more  or  less  distinctly  marked,  and  by 
means  of  such  marking  a  classification  of  three  great  groups  of€wood  is 
Dossible. 

-*. 

(3)  Spring  wood  and' Summer  wood,  the  former  being  the  interior  (first- 
formed  wood  of  the  year),  the  latter  the  exterior  (last-formed)  part  of  the 


256 


THE  MATERIALS  OF  CONSTRUCTION. 


ring.  The  proportion  of  each  and  the  manner  in  which  the  one  merges  into 
the  other  are  sometimes  used,  but  more  frequently  the  manner  in  which  the 
pores  appear  distributed  in  either. 


FIG.  119. — "Ring-porous"  Woods — White  Oak  and  hickory,    a.  r.,  annual  ring;  su.  w. 
summer  wood;  sp.  w.,  spring  wood;  v,  vessels  or  pores;  c.  L,  "  concentric"  lines;  rtt 
darker  tracts  of  bard  fibres  forming  tbe  firm  part  of  oak  wood;  pr,  pitli-rays. 

(4)  Pores,  which  are  vessels  cut  through,  appearing  as  holes  in  cross- 
section,  in  longitudinal  section  as  channels,  scratches,  or  indentations.     (See 
p.  213  and  Figs.  119  and  120.)     They  appear  only  in  the  broad-leaved, 
so-called,  hard  woods;  their  relative  size  (large,  medium,  small,  minute,  and 
indistinct,  when  they  cease  to  be  visible  individually  by  the  naked  eye)  and 
manner  of  distribution  in  the  ring  being  of  much  importance,  and  especially 
in  the  summer  wood,  where  they  appear  singly,  in  groups,  or  short  broken 
lines,  in  continuous  concentric,  often  wavy,  lines,  or  in  radial  branching 
lines. 

(5)  Resin-ducts  (see  p.  210  and  Fig.  118),  which  appear  very  much  like 
pores  in  cross-section,  namely,  as  holes  or  lighter  or  darker  colored  dots,  but 
much  more  scattered.     They  occur   only  in  coniferous  woods,   and  their 
presence  or  absence,  size,  number,  and  distribution  are  an  important  dis- 
tinction in  these  woods. 


i Beech ' Sycamore ! RirftK        i 

FIG.  120. — "  Diffuse  porous  "  Woods,    ar,  annual  ring;  pr,  pith  rays  which  are  "  broad  " 
at  a,  "fine "  at  b,  "  indistinct "  at  d. 

(6)  Pith-rays  (see  Art.  184  and  Figs.  119  and  120),  which  in  cross- 
section  appear  as  radial  lines,  and  in  radial  section  as  interrupted  bands  of 
varying  breadth,  impart  a  peculiar  lustre  to  that  section  in  some  woods. 


TIMBER.  257 

They  are  most  readily  visible  with  the  naked  eye  or  with  a  magnifier  in  the 
"broad-leaved  woods.  In  coniferous  woods  they  are  usually  so  fine  and 
closely  packed  that  to  the  casual  observer  they  do  not  appear.  Their  breadth 
and  their  greater  or  less  distinctness  are  used  as  distinguishing  marks,  being 
styled  fine,  broad,  distinct,  very  distinct,  conspicuous,  and  indistinct  when 
no  longer  visible  by  the  naked  (strong)  eye. 

(7)  Concentric  lines,  appearing  in  the  summer  wood  of  certain  species 
more  or  less  distinct,  resembling  distantly  the  lines  of  pores,  but  much  finer 
and  not  consisting  of  pores.     (See  Fig.  119.) 

Of  microscopic  features,  the  following  only  have  been  referred  to: 

(8)  Tracheids,  a  description  of  which  is  to  be  found  in  Art.  185. 

(9)  Pits,  simple  and  bordered,  especially  the  number  of  simple  pits  in 
the  cells  of  the  pith-rays,  which  lead  into  each  of  the  adjoining  tracheids. 

For  standards  of  weight,  consult  table  in  Art.  191;  for  standards  of 
hardness,  the  classification  in  Art.  203. 

Unless  otherwise  stated  the  color  refers  always  to  the  fresh  cross-section 
of  a  piece  of  dry  wood;  sometimes  distinct  kinds  of  color,  sometimes  only 
shades,  and  often  only  general  color  effects  appear. 

220.  The  Use  of  the  Key. — Nobody  need  expect  to  be  able  to  use  success- 
fully any  key  for  the  distinction  of  woods  or  of  any  other,  class  of  natural 
objects  without  some  practice.  This  is  especially  true  with  regard  to  woods, 
which  are  apt  to  vary  much,  and  when  the  key  is  based  on  such  meagre 
general  data  as  the  present.  The  best  course  to  adopt  is  to  supply  one's  self 
with  a  small  sample  collection  of  woods  accurately  named.*  Small,  polished 
tablets  are  of  little  use  for  this  purpose.  The  pieces  should  be  large  enough, 
if  possible,  to  include  pith  and  bark,  and  of  -sufficient  width  to  permit  ready 
inspection  of  the  cross-section.  By  examining  these  with  the  aid  of  the 
key,  beginning  with  the  better-known  woods,  one  will  soon  learn  to  see  the 
features  described  and  to  form  an  idea  of  the  relative  standards  which  the 
maker  of  the  key  had  in  mind.  To  aid  in  this,  the  accompanying  illustra- 
tions will  be  of  advantage.  When  the  reader  becomes  familiar  with  the  key, 
the  work  of  identifying  any  given  piece  will  be  comparatively  easy.  The 
material  to  be  examined  mast,  of  course,  be  suitably  prepared.  It  should  be 
moistened ;  all  cuts  should  be  made  with  a  very  sharp  knife  or  razor  and  be 
clean  and  smooth,  for  a  bruised  surface  reveals  but  little  structure.  The 
most  useful  cut  may  be  made  along  one  of  the  edges.  Instructive,  thin, 
small  sections  may  be  made  with  a  sharp  penknife  or  razor,  and  when  placed 
on  a  piece  of  thin  glass,  moistened  and  covered  with  another  piece  of  glass, 
they  may  be  examined  by  holding  them  toward  the  light. 

Finding,  on  examination  with  the  magnifier,  that  it  contains  pores,  we 
know  it  is  not  coniferous  or  nonporous.  Finding  no  pores  collected  in  the 
spring-wood  portion  of  the  annual  ring,  but  all  scattered  (diffused)  through 

*  Hough's  Wood  Sections  will  be  found  both  helpful  and  pleasing.-  About  one  hun- 
dred and  fifty  species  of  American  woods  are  now  so  prepared  by  Mr.  Romeyn  Hough, 
Lowville,  N.  Y.— J.  B.  J. 


258  THE  MATERIALS  OF  CONSTRUCTION. 

the  ring,  we  turn  at  once  to  the  class  of  "  diffuse-porous  woods."  We  now 
note  the  size  and  manner  in  which  the  pores  are  distributed  through  th<=» 
ring.  Finding  them  very  small  and  neither  conspicuously  grouped,  nor 
larger  nor  more  abundant  in  the  spring  wood,  we  turn  to  the  third  group  of 
this  class.  We  now  note  the  pith -rays,  and  finding  them  neither  broad  nor 
conspicuous,  but  difficult  to  distinguish  even  with  the  magnifier,  we  at 
once  exclude  the  wood  from  the  first  two  sections  of  this  group  and  place  it 
in  the  third,  which  is  represented  by  only  one  kind,  cottonwood.  Finding 
the  wood  very  soft,  white,  and  on  the  longitudinal  section  with  a  silky  lustre, 
we  are  further  assured  that  our  determination  is  correct.  We  may  now  turn 
to  the  list  of  woods  and  obtain  further  information  regarding  the  occurrence, 
qualities,  and  uses  of  the  wood. 

Sometimes  our  progress  is  not  so  easy;  we  may  waver  in  what  group  or 
section  to  place  the  wood  before  us.  In  such  cases  we  may  try  each  of  the 
doubtful  roads  until  we  reach  a  point  where  we  find  ourselves  entirely  wrong 
and  then  return  and  take  up  another  line;  or  we  may  anticipate  some  of  the 
later-mentioned  features  and,  finding  them  apply  to  our  specimen,  gain 
additional  assurance  of  the  direction  we  ought  to  travel.  Color  will  often 
help  us  to  arrive  at  a  speedy  decision.  In  many  cases,  especially  with  con- 
ifers, which  are  rather  difficult  to  distinguish,  a  knowledge  of  the  locality 
from  which  the  specimen  comes  is  at  once  decisive.  Thus,  Northern  white 
cedar,  and  bald  cypress,  and  the  cedar  of  the  Pacific  will  be  identified  even 
without  the  somewhat  indefinite  criteria  given  in  the  key. 

Engineers  and  architects  can,  in  the  case  of  the  two  leading  kinds  of 
Southern  pine  (long-leaf,  P.  palustns,  and  short-leaf,  P.  ecliinata),  usually 
determine  the  species  by  learning  with  certainty  where  the  lumber  was 
sawed.  This  is  the  more  easy  with  large  orders  as  these  are  filled  directly 
from  the  mills,  and  the  shipping  bills  for  the  particular  cars  on  which  it  is 
delivered  may  be  demanded.  The  two  maps  shown  in  Plates  V  and  VI* 
will  serve  to  identify  the  species  when  the  locality  is  known.  It  will  be 
seen  at  once  that  these  two  species  do  not  often  occupy  the  same  territory. 

221.  KEY  TO  THE  MORE  IMPORTANT  WOODS  OF  NORTH  AMERICA. 

[The  numbers  preceding  names  refer  to  the  List  of  Woods  following  the  Key.] 

I.  Non-porous  Woods. — Pores  not  visible  or  conspicuous  on  cross-section  even 
with  magnifier.     Annual  rings  distinct  by  denser  (dark-colored)  bunds  of  summer 
wood  (Fig.  118). 

II.  Ring-porous  Woods. — Pores  numerous,  usually  visible  on  cross-section  with- 
out magnifier.    Annual  rings'distinct  by  a  zone  of  large  pores  collected  in  the  spring 
wood,  alternating  with  the  denser  summer  wood  (Fig.  119). 

III.  Diffuse-porous   Woods. — Pores  numerous,   usually  not  plainly  visible  on 
cross-section  without  magnifier.     Annual  rings   distinct   by  a  fine  line   of  denser 
summer-wood  cells,  often  quite  indistinct ;  pores  scattered  through  annual  ring,  no 
zone  of  collected  pores  in  spring  wood  (Fig.  120). 

*  These  maps  are  reduced  from  similar  ones  published  by  the  Forestry  Division  of 
the  U.  S.  Agr.  Dept.  Washington,  as  Bulletin  No.  13. 


TIMBER. 

NOTE. — The  above-described  three  groups  are  exogenous,  i.e.,  they  grow  by  add- 
ing annually  wood  on  their  circumference.  A  fourth  group  is  formed  by  the  endog- 
enous woods,  like  yuccas  and  palms,  which  do  not  grow  by  such  additions. 

I.  NON-POROUS  WOODS. 

Includes  all  coniferous  woods. 
A.  Resin-ducts  wanting.* 

1.  No  distinct  heartwood. 

a.  Color  effect  yellowish  white  ;  summer  wood  darker  yellowish  (under 
microscope  pith-ray  without  tracheids) (Nos.  9-13)  FIRS. 

&.  Color  effect  reddish  (roseate)  (under  microscope  pith-ray  with  tra- 
cheids)   (Nos.  14  and  15)  HEMLOCK. 

2.  Heartwood  present,  color  decidedly  different  in  kind  from  sapwood. 

a.  Heartwood  light  orange-red  ;  sapwood  pale  lemon  ;  wood  heavy  and 
hard (No.  38)  YEW. 

6  Heartwood  purplish  to  brownish  red  ;  sapwood  yellowish  white  ;  wood 
soft  to  medium  hard  light,  usually  with  aromatic  odor. 

(No.  6)  RED  CEDAR. 

c.  Heartwood  maroon  to  terra  cotta  or  deep  brownish  red  ;  sapwood  light 
orange  to  dark  amber,  very  soft  and  light,  no  odor  ;  pith-rays  very 
distinct,  specially  pronounced  on  radial  section  . . .  (No.  7)  REDWOOD. 

3.  Heartwood  present,  color  only  different  in  shade   from   sapwood,  dingy- 

yellowish  brown. 

a.  Odorless  and  tasteless (No.  8)  BALD  CYPRESS. 

6.  Wood  with  mild  resinous  odor,  but  tasteless.  .(Nos.  1-4)  WHITE  CEDAR. 
c.   Wood  with  strong  resinous  odor  and  peppery  taste  when  freshly  cut. 

(No.  5)  INCENSE-CEDAR. 

ADDITIONAL  NOTES  FOR  DISTINCTIONS   IN  THE   GROUP. 

Spruce  is  hardly  distinguishable  from  fir,  except  by  the  existence  of  the  resin- 
ducts,  and  microscopically  by  the  presence  of  tracheids  in  the  medullary  rays. 
Spruce  may  also  be  confounded  with  soft  pine,  except  for  the  hetirtwood  color  of  the 
latter  and  the  larger,  more  frequent,  and  more  readily  visible  resin-ducts. 

In  the  lumber-yard  hemlock  is  usually  recognized  by  color  and  the  slivery  char- 
acter of  its  surface.  Western  hemlocks  partake  of  this  last  character  to  a  less 
degree. 

Microscopically  the  white  pine  can  be  distinguished  by  having  usually  only  one 
large  pit,  while  spruce  shows  three  to  five  very  small  pits  in  the  parenchyma-cells  of 
the  pith-ray  communicating  with  the  tracheid. 

The  distinction  of  the  pines  is  possible  only  by  microscopic  examination.  The 
following  distinctive  features  may  assist  in  recognizing,  when  in  the  log  or  lumber- 
pile,  those  usually  found  in  the  market  : 

The  light,  straw  color,  combined  with  great  lightness  and  softness,  distinguishes 
the  white  pines  (white  pine  and  sugar-pine)  from  the  hard  pines  (all  others  in  the 
market),  which  may  also  be  recognized  by  the  gradual  change  of  spring  wood  into 
summer  wood.  This  change  in  hard  pines  is  abrupt,  making  the  summer  wood 
appear  as  a  sharply  defined  and  more  or  less  broad  band. 

The  Norway  pine,  which  may  be  confounded  with  the  short-leaf  pine,  can  be  dis- 

*  To  discover  the  resin-ducts  a  very  smooth  surface  is  necessary,  since  resin-ducts  are  frequently 
seen  only  with  difficulty,  appearing  on  the  cross-section  as  fine  whiter  or  darker  spots  normally  scat- 
tered singly,  rarely  in  groups,  usually  in  the  summer  wood  of  the  annual  ring.  They  are  often  much 
more  easily  seen  on  radial,  and  still  more  so  on  tangential,  sections,  appearing  there  as  fine  lines  or 
dots  of  open  structure  of  different  color,  or  as  indentations  or  pin-scratches  in  a  longitudinal  direction. 


260  THE  MATERIALS  OF  CONSTRUCTION. 

B.  Resin-ducts  present. 

1.  No  distinct  heartwood  ;   color  white,  resin-ducts  very  small,  not  numerous. 

(Nos.  33-36)  SPRUCE. 

2.  Distinct  heartwood  present. 

a.  Resin-ducts  numerous,  evenly  scattered  through  the  ring. 

a'.  Transition  from  spring  wood  to  summer  wood  gradual ;  annual 
ring  distinguished  by  a  fine  line  of  dense  summer-wood  cells  ; 
color  white  to  yellowish  red  :  wood  soft  and  light. 

(Nos.  18-21)  SOFT  PINES.* 

&'.  Transition  from1  spring  wood  to  summer  wood  more  or  less 
abrupt  ;  broad  bands  of  dark-colored  summer  wood  ;  color 
from  light  to  deep  orange  ;  wood  medium  hard  and  heavy. 

(Nos.  22-32)  HARD  PINES.* 
#.  Resin-ducts  not  numerous  nor  evenly  distributed. 

a'.  Color  of  heartwood  orange-reddish,  sapwood  yellowish  (same  as 
hard  pine);  resin-ducts  frequently  combined  in  groups  of  8  to 
30,  forming  lines  on  the  cross-section  (tracheids  with  spirals). 

(No.  37)  DOUGLAS  SPRUCE. 

V.  Color  of  heartwood  light  russett-brown ;  of  sapwood  yellowish 
brown  ;  resin-ducts  very  few,  irregularly  scattered  (tracheids 
without  spirals) (Nos.  16  and  17)  TAMARACK. 

II.     KING-POROUS  WOODS. 

[Some  of  Group  D  and  cedar-elm  imperfectly  ring-porous.  J 

A.  Pores  in  the  summer  wood  minute,  scattered  singly  or  in  groups,  or  in  short 
broken  lines,  the  course  of  which  is  never  radial. 

tinguished  by  being  much  lighter  and  softer.  It  may  also,  but  more  rarely,  be 
confounded  with  heavier  white  pine,  but  for  the  sharper  definition  of  the  annual 
ring,  weight,  and  hardness. 

The  long-leaf  pine  is  strikingly  heavy,  hard,  and  resinous,  and  usually  very  reg- 
ular and  narrow-ringed,  showing  little  sapwood,  and  differing  in  this  respect  from 
the  short-leaf  pine  and  loblolly  pine,  which  usually  have  wider  rings  and  more  sap- 
wood,  the  latter  excelling  in  that  respect. 

The  following  convenient  and  useful  classification  of  pines  into  four  groups, 
proposed  by  Dr.  H.  Mayr,  is  based  on  the  appearance  of  the  pith-ray  as  seen  in  a 
radial  section  of  the  spring  wood  of  any  ring  : 

Section  I.  Walls  of  the  tracheids  of  the  pith-ray  with  dentate  projections. 

a.  One  to  two  large,  simple  pits  to  each  tracheid  on  the  radial  walls  of  the 

cells  of  the  pith-ray. — Group  1.  Represented  in  this  country  only  by  P. 
resinosa. 

b.  Three  to  six  simple  pits  to  each  tracheid,  on  the  walls  of  the  cells  of  the 

pith-ray. — Group  2.  P.  tceda,  palustris,   etc.,    including  most    of   our 

"hard  "  and  "  yellow  "  pines. 

Section  II.  Walls  of  tracheids  of  pith-ray  smooth,  without  dentate  projections. 
a.  One  or  two  large  pits  to  each  tracheid  on  the  radial  walls  of  each  cell  of 

the  pith-ray. — Group  3.  P.  strobus,  lainbertiana,  and  other  true  white 

pines. 
6.  Three  to  six  small  pits  on  the  radial  walls  of  each  cell  of  the  pith-ray. 

Group  4.    P.  parryana  and  other  nut-pines,   including  also  P.  bal- 

fouriana. 

*  Soft  and  hard  pines  are  arbitrary  distinctions,  and  the  two  are  not  distinguishable  at  the  common 
limit. 


TIMBER. 


261 


1.  Pith-rays  minute,  scarcely  distinct. 

a.  Wood  heavy  and  hard;  pores  in  the  summer  wood  not  in  clusters. 

a'.  Color  of  radial  section  not  yellow (Nos.  39-44)  ASH. 

I'.  Color  of  radial  section  light  yellow;  by  which,  together  with  its 
hardness  and  weight,  this  species  is  easily  recognized. 

(No.  103)  OSAGE  ORANGE. 

6.  Wood  light  and  soft;  pores  in  the  summer  wood  in  clusters  of  10  to  30, 

(No.  56)  CATALPA. 

2.  Pith-rays  very  fine,  yet  distinct;  pores  in  summer  wood  usually  single  or 

in  short  lines;  color  of  heartwood  reddish  brown;  of  sapwood  yellowish 
white:  peculiar  odor  on  fresh  section (No.  Ill)  SASSAFRAS. 

3.  Pith-rays  fine,  but  distinct. 

a.  Very  heavy  and  hard;  heartwood  yellowish  brown. 

(No.  77)  BLACK  LOCUST. 
I.  Heavy;  medium  hard  to  hard. 

a.  Pores  in  summer  wood  very  minute,  usually  in  small  clusters  of 
3  to  8;  heartwood  light  orange-brown. 

(No.  83)  RED  MULBERRY. 

b'.  Pores  in  summer  wood  small  to  minute,  usually  isolated;  heart- 
wood  cherry-red (No.  61)  COFFEE-TREE. 

4.  Pith-rays   fine,  but  very   conspicuous,  even  without  magnifier.      Color   of 

heartwood  red;  of  sapwood  pale  lemon (No.  78)  HONEY-LOCUST. 

ADDITIONAL   NOTES   FOR   DISTINCTIONS    IN   THE   GROUP. 

Sassafras  and  mulberry  may  be  confounded  but  for  the  greater  weight  and  hard- 
ness and  the  absence  of  odor  in  the  mulberry;  the  radial  section  of  mulberry  also 
shows  the  pith-rays  conspicuously. 

Honey-locust,  coffee-tree,  and  black-locust  are  also  very  similar  in  appearance. 
The  honey-locust  stands  out  by  the  conspicuousness  of  the  pith-rays,  especially  on 
radial  sections,  on  account  of  their  height,  while  the  black  locust  is  distinguished  by 
the  extremely  great  weight  and  hardness,  together  with  its  darker  brown  color. 


FIG.  121. — Wood  of  Coffee-tree. 

The  ashes,  elms,  hickories,  and  oaks  may,  on  casual  observation,  appear  to 
resemble  one  another  on  account  of  the  pronounced  zone  of  porous  spring  wood. 
The  sharply  defined  large  pith-rays  of  the  oak  exclude  these  at  once;  the  wavy  lines 
of  pores  in  the  summer  wood,  appearing  as  conspicuous  finely-feathered  hatchings 
on  tangential  section,  distinguish  the  elms;  while  the  ashes  differ  from  the  hickory 
by  the  very  conspicuously  defined  zone  of  spring-wood  pores,  which  in  hickory 
appear  more  or  less  interrupted.  The  reddish  hue  of  the  hickory  and  the  more  or 
less  brown  hue  of  the  ash  may  also  aid  in  ready  recognition.  The  smooth,  radial 
surface  of  split  hickory  will  readily  separate  it  from  the  rest. 


262 


THE  MATERIALS  OF  CONSTRUCTION. 


B.  Pores  of  summer  wood  minute  or  small,    in  concentric  wavy  and  sometimes 

branching  lines,  appearing  as  finely-feathered  hatchings  on  tangential 
section. 

1.  Pith-rays  fine,  but  very  distinct;  color  greenish  white.     Heartwood  absent 

or  imperfectly  developed (No.  70)  HACKBERRY. 

2.  Pith-rays  indistinct;  color  of  heartwood  reddish  brown;  sapwood  grayish 

to  reddish  white (Nos.  62-66)  ELMS. 

C.  Pores  of  summer  wood  arranged  in  radial  branching  lines  (when  very  crowded 

radial  arrangement  somewhat  obscured). 

1.  Pith-rays  very  minute,  hardly  visible (Nos.  58-60)  CHESTNUT. 

2.  Pith-rays  very  broad  and  conspicuous (Nos.  84-102)  OAK. 

D.  Pores  of  summer  wood  mostly  but  little  smaller  than  those  of  the  spring  wood, 

isolated  and  scattered;  very  heavy  and  hard  woods.  The  pores  of  the 
spring  wood  sometimes  form  but  an  imperfect  zone.  (Some  diffuse-porous 
woods  of  groups  A  and  B  may  seem  to  belong  here.) 

1.  Fine  concentric  lines  (not  of  pores)  as  distinct,  or  nearly  so,  as  the  very  fine 

pith-rays;  outer  summer  wood  with  a  tinge  of  red;  heartwood  light  reddish 
brown (Nos.  71-75)  HICKORY. 

2.  Fine  concentric  lines,  much  finer  than  the  pith-rays;  no  reddish  tinge  in 

summer  wood;  sapwood  white;  heartwood  blackish.. (No.  105)  PERSIMMON. 


ADDITIONAL   NOTES   FOR   DISTINCTIONS   IN   THE   GROUP. 


A 


B 


FIG.  122.— .1,  Black  Ash;  .B,  White  Ash;   G,  Greeu  Ash. 
The  different  species  of  ash  may  be  identified  as  follows: 

1.  Pores  in  the  summer  wood  more  or  less  united  into  lines. 

a.  The  lines  short  and  broken,  occurring  mostly  near  the  limit  of  the  ring. 

(No.  39,)  WHITE  ASH. 

b.  The  lines  quite  long  and  conspicuous  in  most  parts  of  the  summer 

wood (No.  43)  GREEN  ASH. 

2.  Pores  in  the  summer  wood  not  united  into  lines,  or  rarely  so. 

a.  Heartwood  reddish  brown  and  very  firm. (No.  40)  RED  ASH. 

b.  Heartwood  grayish  brown  and  much  more  porous.  .(No.  41)  BLACK  ASH. 


TIMBER. 


263 


ADDITIONAL  NOTES— continued. 

In  the  oaks  two  groups  can  be  readily  distinguished  by  the  manner  in  which  the 
pores  are  distributed  in  the  summer -wood.  In  the  white  oaks  the  pores  are  very  fine 
and  numerous  and  crowded  in  the  outer  part  of  the  summer  wood,  while  in  the  black 
or  red  oaks  the  pores  are  larger,  few  in  number,  and  mostly  isolated.  The  live  oaks, 
as  far  as  structure  is  concerned,  belong  to  the  black  oaks,  but  are  much  less  porous, 
and  are  exceedingly  heavy  and  hard. 


FJG.  123.— Wood  of  Red  Oak.     (For  White  Oak  see  Fig.  119.) 


FJG.  124.— Wood  of  Chestnut. 


FIG.  125.— Wood  of  Hickory. 


264 


TEE  MATERIALS  OF  CONSTRUCTION. 


III.    1>J  ^FUSE-POROUS  WOODS. 

[A  few  indistinctly  ring-porous  woo«  i  of  Group  II,  D,  and  cedar-elm  may  seem  to  belong  here.] 

A.  Pores  varying  in  size  from  large  to  minute;  largest  in  spring  wood,  thereby  giving 

sometimes  the  appearance  of  a  ring-porous  arrangement. 

1,  Heavy  and  hard;  color  of  heartwood  (especially  on  longitudinal  section) 

chocolate-brown, (No.  116)  BLACK  WALNUT. 

2.  Light  and  soft;  color  of  heartwood  light  reddish  brown..(No.  55)  BUTTERNUT. 

B.  Pores  all  minute  and  indistinct;  most  numerous  in  spring  wood,  giving  rise  to  a 

lighter-colored  zone  or  line  (especially  on  longitudinal  section),  thereby 
appearing  sometimes  ring-porous;  wood  hard,  heartwood  vinous-reddish; 
pith-rays  very  fine,  but  very  distinct.  (See  also  the  sometimes  indistinct 
ring-porous  cedar-elm,  and  occasionally  winged  elm,  which  are  readily 
distinguished  by  the  concentric  wavy  lines  of  pores  in  the  summer  wood.) 

(No.  57j  CHERRY. 

C.  Pores  minute  or  indistinct,  neither  conspicuously  larger  nor  more  numerous  in 

the  spring  wood  and  evenly  distributed. 
1.  Broad  pith-rays  present. 

a.  All  or  most  pith-rays  broad,  numerous,  and  crowded,  especially  on  tan- 
gential sections,  medium  heavy  and  hard,  difficult  to  split. 

(Nos.  112  and  113)  SYCAMORE. 
6.  Only  part  of  the  pith-rays  broad. 

a'.  Broad  pith-rays  well  defined,  quite  numerous;  wood  reddish  white 
to  reddish (No.  47)  BEECH. 

I'.  Broad  pith-rays  not  sharply  defined,  made  up  of  many  small  rays, 
not  numerous.  Stem  furrowed,  and  therefore  the  periphery 
of  section,  and  with  it  the  annual  rings,  sinuous,  bending  in 
and  out,  and  the  large  pith-rays  generally  limited  to  the  fur- 
rows or  concave  portions.  Wood  white,  not  reddish. 

(No.  52)  BLUE  BEECH. 


DDITIONAL   NOTES   FOR  DISTINCTIONS   IN   THE   GROUP. 

Cherry  and  birch  are  sometimes  confounded.   The  high  pith-rays  on  the  cherry  on 

radial  sections  readily  distinguish  it;  distinct  pores  on  birch  and  spring-wood  zone 

in  cherry,  as  well  as  the  darker  vinous-brown  color  of  the  latter,  will  prove  helpful. 

Two  groups  of  birches  can  be  readily  distinguished,  though  specific  distinction  is 

not  always  possible. 

1.  Pith-rays  fairly  distinct,  the  pores  rather  few  and  not  more  abundant  in  the 
spring  wood;  wood  heavy,  usually  darker. 

(No.  48)  CHERRY-BIRCH  and  (No.  49)  YELLOW  BIRCH. 


H 


pr,.- 

Beech ! Sycamore ! Birch -_-j 

FIG.  126.— Wood  of  Beech,  Sycamore,  aud  Birch. 


TIMBER. 


265 


2,  No  broad  pith-rays  present. 

a.  Pith-rays  small  to  very  small,  but  quite  distinct. 
a'.  Wood  hard. 

a".  Color  reddish  white,  with  dark  reddish  tinge  in  outer  sum- 
mer wood  ........................  (Nos.  79-82)  MAPLE. 

I".  Color  white,  without  reddish  tinge  ........  (No.  76)  HOLLY. 

&'.  Wood  soft  to  very  soft. 

a".  Pores  crowded,  occupying  nearly  all  the  space   between 
pith-rays. 

a'".  Color  yellowish  white,  often  with  a  greenish  tinge 
in  heartwood  ...........  (No.  115)  TULIP-POPLAR. 

(No.  116)  CUCUMBER-TREE. 

V".  Color  of  sapwood  grayish,  of  heartwood  light  to 
dark  reddish  brown  ........  (No.  69)  SWEET  GUM. 

6".  Pores  not  crowded,  occupying  not  over  one  third  the  pith- 

rays;  heartwood  brownish  white  to  very  light  brown. 

(Nos.  45  and  46)  BASSWOOD. 

5.  Pith-rays  scarcely  distinct,   yet  if  viewed   with  ordinary  magnifier 
plainly  visible. 
a'.  Pores  indistinct  to  the  naked  eye. 

a".  Color  uniform  pale  yellow;  pith-rays  not  conspicuous  even 
on  the  radial  section  .........  (Nos.  53  and  54)  BUCKEYE. 

6".  Sapwood  yellowish  gray,  heartwood  grayish  brown;  pith- 
rays  conspicuous  on  the  radial  section. 

(Nos.  67,  68)  SOUR  GUM. 

&'.  Pores  scarcely  distinct,  but  mostly  visible  as  grayish  specks  on  the 
cross-section  ;  sapwood  whitish,  heartwood  reddish. 

(Nos.  48-51)  BIRCH. 

3.  Pith-rays  not  visible  or  else  indistinct,  even  if  viewed  with  magnifier. 

1.  WTood  very  soft,  white,  or  in  shades  of  brown,  usually  with  a  silky  lustre. 

(NOS.  105-110)  COTTONWOOD  (POPLAR). 


2.  Pith-rays  barely  distinct,  pores  more  numerous  and  commonly  forming  a 
more  porous  spring-wood  zone;  wood  of  medium  weight. 

(No.  51)  CANOE-  OR  PAPER-BIRCH. 
The  species  of  maple  may  be  distinguished  as  follows: 

1.  Most  of  the  pith-rays  broader  than  the  pores  and  very  conspicuous. 

(No.  79)  SUGAR  MAPLE. 


FIG.  127.- Wood  of  Maple. 


266 


THE  MATERIALS  OF  CONSTRUCTION. 


ADDITIONAL  NOTES — continued. 

2.  Pith-rays  not  or  rarely  broader  than  the  pores,  fine  but  conspicuous. 

a.  Wood  heavy  and  hard,  usually  of  darker  reddish  color  and  commonly 

spotted  on  cross-section (No.  80)  RED  MAPLE. 

b.  Wood  of  medium  weight  and  hardness,  usually  light-colored. 

(No.  82)  SILVER  MAPLE. 

Red  maple  is  not  always  safely  distinguished  from  soft  maple.     In  box-elder  the 
pores  are  finer  and  more  numerous  than  in  soft  maple. 

The  various  species  of  elm  may  be  distinguished  as  follows: 

1.  Pores  of  spring  wood  form  a  broad  band  of  several  rows;  easy  splitting,  dark 

brown  heart (No.  64)  RED  ELM. 

2.  Pores  of  spring  wood  usually  in  a  single  row,  or  nearly  so. 

a.  Pores  of  spring  wood  large,  conspicuously  so (No  62)  WHITE  ELM. 

b.  Pores  of  spring  wood  small  to  minute. 

a  .  Lines  of  pores  in  summer  wood  fine,  not  as  wide  as  the  interme- 
diate spaces,  giving  rise  to  very  compact  grain, 

(No.  63)  ROCK-ELM. 

V.  Lines  of  pores  broad,  commonly  as  wide  as  the  intermediate  spaces. 

(No.  66)  WINGED  ELM. 

c.  Pores  in  spring  wood  indistinct,  and  therefore  hardly  a  ring-porous 

wood (No.  65)  CEDAR-ELM. 


FIG.  128.— Wood  of  Elm.     «,  Red  Elm;  b,  White  Elm;  c,  Winged  Elm. 


FIG.   129.— Walnut,     p    r.,  pith-rays; 
c.  L,  concentric   Hues;  D,    vessels  or 
pores;  su.  w.,  summer  wood;  sp.  w. 
spring  wood. 


FIG.  130.— Wood  of  Cherry. 


TIMBER. 


267 


LIST  OF  THE  MORE  IMPORTANT  WOODS  OF  THE  UNITED  STATES.* 

[Arranged  alphabetically.] 

NOTE. — In  the  following  descriptions  the  terms  expressing  size  have  been  used 
with  the  following  meanings  : 

Small  =  trees  of  50  feet  high  or  less. 
Medium  =     "      "  50  to  100  feet  high. 

Large  =     "      "  over  100  feet  in  height. 
All  these  terms  must  be  understood  as  having  been  used  as  approximate  estimates  only. 

A.  CONIFEROUS  WOODS. 

Woods  of  simple  and  uniform  structure,  generally  light,  soft  but  stiff; 
abundant  in  suitable  dimensions  and  forming  by  far  the  greatest  part  of  all 
the  lumber  used. 

222.  Cedar. — Light,  soft,  stiff,  not  strong,  of  fine  texture;  sap  and  heart- 
wood  distinct,  the  former  lighter,  the  latter  a  dull  grayish  brown  or  red. 
The  wood  seasons  rapidly,  shrinks  and  checks  but  little,  and  is  very  dur- 
able. Used  like  soft  pine,  but  owing  to  its  great  durability  preferred  for 
shingles,  etc.  Small  sizes  used  for  posts,  ties,  etc.  Cedars  usually  occur 
scattered,  but  they  form,  in  certain  localities,  forests  of  considerable  extent. 

a.  White  Cedars. — Heartwood  a  light  grayish  brown. 


1,  WHITE  CEDAR  (Thuya  occidentalis)  (Arbor- 
vitse):  Scattered  along  streams  and  lakes,  frequently 
covering  extensive  swamps;  rarely  large  enough  for 
lumber,  but  commonly  used  for  posts,  ties,  etc. 
Maine  to  Minnesota  and  northward. 


FIG.  131.— T.  occidentalis. 

2.  CANOE-OEDAK  (Thuya  gigantea)  (red  cedar  of 
the  West) :  In  Oregon  and  Washington  a  very  large 
tree,  covering  extensive  swamps;  in  the  mountains 
much  smaller,  skirting  the  watercourses;  an  impor- 
tant lumber  tree.  Washington  to  northern  California 
and  eastward  to  Montana. 


FIG.  182.  —  T.  gigantea. 


*  The  text  here  is  from  U.  S.  Forestry  Bulletin  No.  10,  while  many  of  the  cuts  are 
from  Apgar's  Trees  of  the  Northern  States.  The  remaining  cuts  have  been  specially 
drawn  for  this  work,  under  the  direction  of  Dr.  William  Treiease,  Director  of  the  Mis- 
souri Botanical  Garden,  St.  Louis. 


268 


THE  MATERIALS  OF  CONSTRUCTION 


3.  WHITE  CEDAR  (Chamcecyparis  thy  aides): 
Medium-sized  tree,  wood  very  light  and  soft.  Along 
the  coast  from  Maine  to  Mississippi. 


FIG.  133.— C.  thy  aides. 


4.  WHITE  CEDAR  (ChamcBcyparis  lawsomana) 
(Port  Orford  cedar,  Oregon  cedar,  Lawson's  cypress, 
ginger-pine):  A  very  large  tree,  extensively  cut  for 
lumber;  heavier  and  stronger  than  the  preceding. 
Along  the  coast-line  of  Oregon. 


Fie*.  131.  —  C.  lawsoniana. 


5.  WHITE  CEDAR  (Libocedrus  decur- 
rens]  (incense-cedar) :  A  large  tree,  abun- 
dantly scattered  among  pine  and  fir> 
wood  fine-grained.  Cascades  and  Sierra 
Nevada  of  Oregon  and  California. 


S  K 

FIG.  135. — L.  decurrens. 


TIMBER. 


269 


b.  Red  Cedars.— Heartwood  red. 

6.  RED  CEDAR  (Juniperus  virginiana)  (Savin  juniper) :  Similar  to 
white  cedar,  but  of  somewhat  finer  texture.  Used  in  cabinet  work  in 
cooperage,  for  veneers,  and  especially  for  lead-pencils, 
for  which  purpose  alone  several  million  feet  are  cut 
each  year.  A  small  to  medium-sized  tree  scattered 
through  the  forests,  or,  in  the  West,  sparsely  covering 
extensive  areas  (cedar-brakes).  The  red  cedar  is  the 
most  widely  distributed  conifer  of  the  United  States, 
occurring  from  the  Atlantic  to  the  Pacific  and  from  _ 
Florida  to  Minnesota,  but  attains  a  suitable  size  for  T 
lumber  only  in  the  Southern,  and  more  especially  the  FlG"  '  36-~t 
Gulf,  States. 


ana. 


7.  REDWOOD  (Sequoia  sempervirens) :  Wood  in 
its  quality  and  uses  like  white  cedar;  the  narrow 
sapwood  whitish;  the  heartwood  light  red,  soon 
turning  to  brownish  red  when  exposed.  A  very 
large  tree,  limited  to  the  coast  ranges  of  Cali- 
fornia, and  forming  considerable  forests,  which 
are  rapidly  being  converted  into  lumber. 


FIG.  137. — 8.  sempervirens. 


223.   Cypress. 

8.  CYPRESS  (Taxodium  disticlmm)  (bald 
cypress ;  black,  white,  and  red  cypress) :  Wood  in 
appearance,  quality,  and  uses  similar  to  white 
cedar.  "  Black  cypress  "  and  "  white  cypress"  are 
heavy  and  light  forms  of  the  same  species.  The 
cypress  is  a  large  deciduous  tree,  occupying  much 
of  the  swamp  and  overflow  land  along  the  coast 
and  rivers  of  the  Southern  States. 


FIG.  138.— T.  disticlium. 

224.  Fir. — This  name  is  frequently  applied  to  wood  and  to  trees  which 
are  not  fir;  most  commonly  to  spruce,  but  also,  especially  in  English  mar- 
kets, to  pine.  It  resembles  spruce,  but  is  easily  distinguished  from  it,  as 
well  as  from  pine  and  larch,  by  the  absence  of  resin-ducts.  Quality,  uses, 
and  habits  similar  to  spruce. 


£70 


THE  MATERIALS  OF  CONSTRUCTION. 


9.  BALSAM-FIR  (Abiesbalsamea) :  A  medium-sized 
tree  scattered  throughout  the  northern  pineries;  cut, 
in  lumber  operations,  whenever  of  sufficient  size,  and 
sold  with  pine  or  spruce.  Minnesota  to  Maine  and 
northward. 


FIG.  139. — A.  balsamea. 

10.  WHITE  FIE  (Abies  grandis  and  Abies  cdncolor 
large-sized  tree,  forming 
an  important  part  of  most 
of  the  Western  mountain- 
forests,  and  furnishing 
much  of  the  lumber  of  the 
respective  regions.  The 
former  occurs  from  Van- 
couver to  central  Cali- 
fornia and  eastward  to 
Montana;  the  latter  from 
Oregon  to  Arizona  and 
eastward  to  Colorado  and 
New  Mexico. 


Medium  to  very 


& 

/IG.  140.— A  grandis. 


FIG.  141.— A.  concolor. 


11.  WHITE  FIR  (Abies  amabilis): 
Good-sized  tree,  often  forming  exten- 
sive mountain-forests.  Cascade 
Mountains  of  Washington  and  Oregon. 


FIG.  142. — A.  amabilis. 


TIMBER. 


271 


12.  RED  FIR  (Abies  nobilis)  (not  to  be  con- 
founded with  Douglas  fir;  see  No.  37):  Large  to 
very  large  tree,  forming  with  A.  amabilis  extensive 
forests  on  the  slope  of  the  mountains  between  3000 
and  4000  feet  elevation.  Cascade  Mountains  of 
Oregon. 


CO 

FIG.  143.— A  nobilis. 


13.  BED  FIR  (Abies  magnified):  Very 
large  tree,  forming  forests  about  the  base 
of  Mount  Shasta.  Sierra  Nevada  of  Cali- 
fornia, from  Mount  Shasta  southward. 


FIG.  144. — A.  magnified. 

225.  Hemlock. — Light  to  medium  weight,  soft,  stiff  but  brittle,  com- 
monly cross-grained,  rough  and  splintery;  sapwood  and  heartwood  not  well 
defined ;  the  wood  of  a  light,  reddish-gray  color,  free  from  resin-ducts, 
moderately  durable,  shrinks  and  warps  considerably,  wears  rough,  retains 
nails  firmly.  Used  principally  for  dimension  stuff  and  timbers.  Hemlocks 
are  medium  to  large-sized  trees,  commonly  scattered  among  broad-leaved 
trees  and  conifers,  but  often  forming  forests  of  almost  pure  growth. 


14.  HEMLOCK  (Tsuga  canadensis):  Medium- 
sized  tree,  furnishes  almost  all  the  hemlock  of  the 
Eastern  market.  Maine  to  Wisconsin.;  also  following 
the  Alleghanies  southward  to  Georgia  and  Alabama. 


FIG.  145. — 7\  canaden- 


272 


THE  MATERIALS  OF  CONSTRUCTION. 


-' 


15.  HEMLOCK  (Tsuga  mertensiand):  Large- 
sized  tree;  wood  claimed  to  be  heavier  and  harder 
than  the  Eastern  form  and  of  superior  quality. 
Washington  to  California  and  eastward  to  Mon- 
tana. 


FIG.  146. — T.  mertensiana. 

226.  Larch  or  Tamarack. — Wood  like  the  best  of  hard  pine  both  in  ap- 
pearance, quality,  and  uses,  and,  owing  to  its  great  durability,  somewhat  pre- 
ferred in  ship-building,  for  telegraph-poles  and  railroad-ties.  In  its  struc- 
ture it  resembles  spruce.  The  larches  are  deciduous  trees,  occasionally 
covering  considerable  areas,  but  usually  scattered  among  other  conifers. 


10.  TAMARACK  (Larix  americana)  (Hackma- 
tack) :  Medium-sized  tree,  often  covering  swamps, 
in  which  case  it  is  smaller  and  of  poor  quality. 
Maine  to  Minnesota,  and  southward  to  Pennsyl- 
vania. 


FIG.  147. — L.  amtricana. 


17.  TAMARACK  (L.  occidentalis):  Large-sized  trees, 
scattered,  locally  abundant.  Washington  and  Oregon  to 
Montana. 


FIG.     148.— L.     occi- 
dentalis. 


TIMBER.  273 

227.  Pine. — Very  variable,  very  light  and  soft  in  "soft"  pine,  such  as 
white  pine;  of  medium  weight  to  heavy  and  quite  hard  in  "  hard  "  pine,  of 
which  long-leaf  or  Georgia  pine  is  the  extreme  form.  Usually  it  is  stiff, 
quite  strong,  of  even  texture,  and  more  or  less  resinous.  The  sapwood  is 
yellowish  white;  the  heartwood,  orange-brown.  Pine  shrinks  moderately, 
seasons  rapidly  and  without  much  injury;  it  works  easily;  is  never  too  hard 
to  nail  (unlike  oak  or  hickory);  it  is  mostly  quite  durable,  and  if  well  sea- 
soned is  not  subject  to  the  attacks  of  boring-insects.  The  heavier  the  wood, 
the  darker,  stronger,  and  harder  it  is,  and  the  more  it  shrinks  and  checks. 
Pine  is  used  more  extensively  than  any  other  kind  of  wood.  It  is  the  prin- 
cipal wood  in  common  carpentry,  as  well  as  in  all  heavy  construction, 
bridges,  trestles,  etc.  It  is  also  used  in  almost  every  other  wood  iudusti^ 
for  spars,  masts,  planks,  and  timbers  in  ship-building,  in  car  and  wagon  con- 
struction, in  cooperage,  for  crates  and  boxes,  in  furniture  work,  for  toys  and 
patterns,  railway-ties,  water-pipes,  excelsior,  etc.  Pines  are  usually  large 
trees  with  few  branches,  the  straight,  cylindrical,  useful  stem  forming  by 
far  the  greatest  part  of  the  tree;  they  occur  gregariously,  forming  vast 
forests,  a  fact  which  greatly  facilitates  their  exploitation.  Of  the  many 
special  terms  applied  to  pine  as  lumber,  denoting  sometimes  differences  in 
quality,  the  following  deserve  attention: 

"White  pine,"  '''pumpkin-pine,"  "soft  pine,"  in  the  Eastern  markets  re- 
fer to  the  wood  of  the  white  pine  (Pi mis  strobus),  and  on  the  Pacific  Coast 
to  that  of  the  sugar-pine  (Pinus  lambertiana). 

(i  Yellow  pine  "  is  applied  in  the  trade  to  all  the  Southern  lumber  pines; 
in  the  Northeast  it  is  also  applied  to  the  pitch-pine  (P.  rigidci);  in  the  West 
it  refers  mostly  to  bull-pine  (P.  ponderosa). 

"  Yellow  long-leaf  pine,"  "  Georgia  pine,"  are  terms  which  refer  to  long- 
leaf  pine  (P.  palustris). 

"  Hard  pine  "  is  a  common  term  in  carpentry,  and  applies  to  everything 
except  white  pine. 

"  Pitch-pine"  includes  all  Southern  pines  and  also  the  true  pitch-pine 
(P.  rigida),  but  is  mostly  applied,  especially  in  foreign  markets,  to  the 
wood  of  the  long-leaf  pine  (P.  .palustris). 

For  the  great  variety  of  confusing  local  names  applied  to  the  Southern 
pines  in  their  homes,  part  of  which  have  been  adopted  in  the  markets  of 
the  Atlantic  seaboard,  see  report  of  Chief  of  Division  of  Forestry  for  1891, 
page  212,  etc.,  and  also  the  list  below. 


274 


THE  MATERIALS  OF  CONSTRUCTION. 


a.  Soft  Pines. 

18.  WHITE  PINE  (Pinus  strobus) :  Large  to  very 
large-sized  tree;  for  the  last  fifty  years  the  most  im- 
portant timber  tree  of  the  Union,  furnishing  the 
best  quality  of  soft  pine.  Minnesota,  Wisconsin 
Michigan,  New  England,  along  the  Alleghanies  to 


FIG.  149.—  P.  strobus. 


\19.  SUGAR-PINE  (Pinus  lambertiana):  A  very 
^  large  tree,  together  with  Abies  concolor,  forming 
extensive  forests;  important  lumber  tree, 
and  California. 


Oregon 


FIG.  150. — P.  lambertiana. 

20.  WHITE  PINE  (Pinus  monticola} :  A  large 
tree,  at  home  in  Montana,  Idaho,  and  the  Pacific 
States;  most  common  and  locally  used  in  northern 
Idaho. 


FIG.  151.-  P.  monticola. 

21.  WHITE  PIKE  (Pinus  ftexilis) :  A  small  tree, 
forming  mountain-forests  of  considerable  extent 
and  locally  used;  eastern  Rocky  Mountain  slopes; 
Montana  to  New  Mexico. 


FIG.  152.— P.  flexilis. 


TIMBER. 


215 


b.  Hard  Pines. 

22.  LONG-LEAF  PINE  (Pinus  palustris) 
(Georgia  pine,  yellow  pine,  long  straw-pine,  etc.) : 
Large  tree;  forms  extensive  forests  and  furnishes 
the  hardest  and  strongest  pine  lumber  in  the  mar- 
ket. Coast  region  from  North  Carolina  to  Texas. 


FIG.  153.— P.  palustris. 

23.  BULL-PINE  (Pinus  ponderosa)  (yellow 
pine):  Medium  to  very  large-sized  tree,  forming 
extensive  forests  in  Pacific  and  Rocky  Mountain 
regions;  furnishes  most  of  the  hard  pine  of  the 
West;  sapwood  wide;  wood  very  variable. 


FIG.  154. — P.  ponderosa. 

24.  LOBLOLLY  PINE  (Pinus  tceda)  (slash-pine, 
old  field-pine,  rosemary-pine,  sap-pine,  short  straw- 
pine,  etc.) :  Large-sized  tree,  forms  extensive 
forests;  wider-ringed,  coarser,  lighter,  softer,  with 
more  sapwood  than  the  long-leaf  pine,  but  the  two 
often  confounded.  This  is  the  common  lumber 
pine  from  Virginia  to  South  Carolina,  and  is 
found  extensively  in  Arkansas  and  Texas. 
Southern  States;  Virginia  to  Texas  and  Arkansas. 


FIG.  155.— P.  tceda. 


25.  NORWAY  PINE  (Pinus  resinosa):  Large- 
sized  tree,  never  forming  forests,  usually  scattered 
or  in  small  groves,  together  with  white  pine;  largely 
sapwood  and  hence  not  durable.  Minnesota  to- 
Michigan;  also  in  New  England  to  Pennsylvania. 


FIG.  156. — P.  resinosa. 


276 


THE  MATERIALS  OF  CONSTRUCTION. 


26.  SHORT-LEAF  PINE  (Pinus  ecMnata] 
(slash-pine,,  Carolina  pine,  yellow  pine,  old  field- 
pine,  etc.):  Resembles  loblolly  pine;  often  ap- 
proaches in  its  wood  the  Norway  pine.  The 
common  lumber  pine  of  Missouri  and  Arkansas. 
North  Carolina  to  Texas  and  Missouri. 


FIG.  157.— P.  ecMnata. 

27.  CUBAN  PINE  (Pinus  cubensis]  (slash-pine,  swamp- 
pine,  bastard-pine,  meadow-pine) :  Resembles  long-leaf  pine, 
but  commonly  has  wider  sapwood  and  coarser  grain;  does 
not  enter  the  markets  to  any  great  extent.  Along  the 
coast  from  South  Carolina  to  Louisiana. 


FIG.  158.—  P.   cu- 
bensis. 

28.  BULL-PINE  (Pinus  jeffreyi) 
(black  pine) :  Large-sized  tree,  wood  re- 
sembling bull-pine  (P.  ponderosa);  used 
locally  in  California,  replacing  P. 
derosa  at  high  altitudes. 


FIG.  159.— P.  jeffreyi. 

The  following  are  small  to  medium-sized  pines, 
not  commonly  offered  as  lumber  in  the  market; 
used  locally  for  timber,  ties,  etc. : 

29.  BLACK  PINE  (Pinus  murrayand)  (lodge- 
pole  pine,  tamarack):  Rocky  Mountains  and 
Pacific  regions. 


FIG.  160. — P.  murrayana. 


TIMBER. 


277 


30.  PITCH-PINE  (Pinus  rigida):  Along  the 
coast  from  New  York  to  Georgia,  and  along  the 
mountains  to  Kentucky. 


FIG.  161.— P.  rig ida. 

31.  JERSEY  PINE  (Pinus  inops)  (scrub-pine) 
As  before. 


FIG.  163. — P.  banksiana. 


FIG.  162.— P.  inops. 

32.  GRAY  PIXE  (Pinus  banksiana)  (scrub- 
pine)  :  Maine,  Vermont,  and  Michigan  to  Minne- 
sota. 

Redwood.     See  CEDAR. 

228.  Spruce. — Resembles  soft  pine,  is  light, 
very  soft,  stiff,  moderately  strong,  less  resinous  than 
pine;  has  no  distinct, heartwood,  and  is  of  whitish  color.  Used  like  soft 
pine,  but  also  employed  as  resonance-wood  and  preferred  for  paper  pulp. 
Spruces,  like  pines,  form  extensive  forests;  they  are  more 'frugal,  thrive  on 
thinner  soils,  and  bear  more  shade,  but  usually  require  a  more  humid  cli- 
mate. "Black"  and  "white"  spruce,  as  applied  by  lumbermen,  usually 
refer  to  narrow-  and  wide-ringed  forms  of  the  black  spruce  (Picea  nigra). 


33.  BLACK  SPRUCE  (Picea  nigra) :  Medium- 
sized  tree,  forms  extensive  forests  in  northeastern 
United  States  and  in  British  America;  occurs 
scattered  or  in  groves,  especially  in  low  lands 
throughout  the  Northern  pineries.  Important 
lumber  tree  in  Eastern  United  States.  Maine  to 
Minnesota,  British  America,  and  on  the  Allegha- 
nies  to  North  Carolina. 


FIG.  164.— P.  nigra. 


278 


THE  MATERIALS  OF  CONSTRUCTION. 


34.  WHITE  SPRUCE  (Picea  alba) :  Generally 
associated  with  the  preceding;  most  abundant 
along  streams  and  lakes,  grows  largest  in  Mon- 
tana, and  forms  the  most  important  tree  of  the 
subarctic  forest  of  British  America.  Northern 
United  States,  from  Maine  to  Minnesota,  also 
from  Montana  to  Pacific,  British  America. 


FIG.  165.— P.  alba. 

35.  WHITE  SPRUCE  (Picea  engelmanni): 
Medium  to  large-sized  tree,  forming  extensive 
forests  at  elevations  from  5000  to  10,000  feet 
above  sea-level;  resembles  the  preceding,  but  occu- 
pies a  different  station.  A  very  important  timber 
tree  in  the  central  and  southern  parts  of  the 
Rocky  Mountains.  Rocky  Mountains  from  Mexico 
to  Montana. 


FIG.  166. — P.  engelmanni. 

36.  TIDE-LAND  SPRUCE  (Picea  sitchensis):  A 
large-sized  tree,  forming  an  extensive  coast-belt 
forest.  Along  the  seacoast  from  Alaska  to  central 
California. 

Bastard  Spruce. — Spruce  or  fir  in  name, 
but  resembling  hard  pine  or  larch  in  the  appear- 
ance, quality,  and  uses  of  its  wood. 

FIG.  167.— P.  sitchensis. 

37.  DOUGLAS  SPRUCE  (Pseudotsuga  doug- 
lasii)  (yellow  fir,  red  fir,  Oregon  pine) :  One  of 
the  most  important  trees  of  the  Western  United 
States;  grows  very  large  in  the  Pacific  States, 
to  fair  size  in  all  parts  of  the  mountains,  in 
Colorado  up  to  about  10,000  feet  above  sea- 
level;  forms  extensive  forests,  often  of  pure 
growth.  Wood  very  variable,  usually  coarse- 
grained and  heavy,  with  very  pronounced  sum- 
mer wood,  hard  and  strong  ("red"  fir),  but 
often  fine-grained  and  light  ("  yellow  "  fir).  It 
replaces  hard  pine  and  is  especially  suited  to 
heavy  construction.  From  the  plains  to  the 
FIG.  168.— P.  douglasii.  Pacific  Ocean  ;  from  Mexico  to  British  America. 


TIMBER. 


279 


Tamarack.  See  LARCH. 
229,  Yew. — Wood  heavy,  hard,  extremely  stiff  and  strong,  of  fine  tex- 
ture, with  a  pale  yellow  sapwood  and  an  orange- 
red  heart;  seasons  well  and  is  quite  durable. 
Yew  is  extensively  used  for  archery,  bows,  turn- 
er's ware,  etc.  The  yews  form  no  forests,  but 
occur  scattered  with  other  conifers. 


38.  YEW  (Taxus  brevifolia):  A  small  to 
medium-sized  tree  of  the  Pacific  region. 


FIG.  169.— T.  brevifolia. 

B.    BROAD-LEAVED    WOODS,     (HARDWOODS.) 

Woods  of  complex  and  very  variable  structure  and  therefore  differing 
widely  in  quality,  behavior,  and  consequently  in  applicability  to  the  arts. 

230.  Ash. — Wood  heavy,  hard,  strong,  stiff,  quite  tough,  not  durable  in 
contact  with  soil,  straight-grained,  rough  on  the  split  surface  and  coarse  in 
texture.  The  wood  shrinks  moderately,  seasons  with  little  injury,  stands 
well  and  takes  a  good  polish.  In  carpentry  ash  is  used  for  finishing  lumber, 
stairways,  panels,  etc.;  it  is  used  in  ship-building,  in  the  construction  of 
cars,  wagons,  carriages,  etc.,  in  the  manufacture  of  farm-implements, 
machinery,  and  especially  of  furniture  of  all  kinds,  and  also  for  harness 
work;  for  barrels,  baskets,  oars,  tool-handles,  hoops,  clothespins,  and  toys. 
The  trees  of  the  several  species  of  ash  are  rapid  growers,  of  small  to  medium 
height  with  stout  trunks;  they  form  no  forests,  but  occur  scattered  in 
almost  all  our  broad-leaved  forests. 


39.  WHITE  ASH  (Fraxinus  americana): 
Medium,  sometimes  large-sized  tree.  Basin  of 
the  Ohio,  but  found  from  Maine  to  Minnesota 
and  Texas. 


FIG.  170  —  F.  americana. 


280 


THE  MATERIALS  OF  CONSTRUCTION. 


40.  RED  ASH  (Fraxinus  pulescens) :  Small-sized 
tree.  North  Atlantic  States,  but  extends  to  the 
Mississippi. 


FIG.  171.— F.  pubesccns. 

41.  BLACK  ASH  (Fraxinus  sambucifolia)  (hoop- 
ash,  ground-ash):  Medium-sized  tree,  very  common. 
Maine  to  Minnesota,  and  southward  to  Virginia  and 
Arkansas. 


FIG.    172.—  F.    sambuci- 
folia. 

42.  BLUE    ASH    (Fraxinus    quadrangulata): 

Small  to  medium-sized.  Indiana  and  Illinois; 
occurs  from  Michigan  to  Minnesota  and  southward 
to  Alabama. 


FIG.    173. — F.     quadrangu- 
lata. 


43.  GKEEN  ASH  (Fraxinus  viridis):  Small- 
sized  tree.  New  York  to  the  Rocky  Mountains, 
and  southward  to  Florida  and  Arizona. 


FIG.  174.— #  viridis 


TIMBER 


281 


44.  OREGON  ASH  (Fraxinus  oregana): 
Medium-sized  tree.  Western  Washington 
to  California. 


FIG.  175.— F.  oregana. 


Aspen.     See  POPLAR. 
231.  Basswood. 

45.  BASSWOOD  (Tilia  americana)  (lime-tree, 
American  linden,  lin,  bee-tree):  Wood  light,  soft, 
stiff  but  not  strong,  of  fine  texture,  and  white  to 
light  brown  color.  The  wood  shrinks  considerably 
in  drying,  works  and  stands  well;  it  is  used  in  car- 
pentry, in  the  manufacture  of  furniture  and  wood- 
enware,  both  turned  and  carved,  ih  cooperage,  for 
toys,  also  for  panelling  of  car  and  carriage  bodies. 
Medium  to  large-sized  tree,  common  in  all' Northern 
broad-leaved  forests;  found  throughout  the  Eastern 
FIG.  176.-T.  americana.  United  States. 


46.  WHITE  BASSWOOD  (Tilia  heterophylla) :  A 
small-sized  tree  most  abundant  in  the  Alleghauy 
region. 


FIG.   177.— T.  lietero- 
phylla. 


282 


THE  MATERIALS  OF  CONSTRUCTION. 


232.  Beech. 

47.  BEECH  (Fagus  ferruginea):  Wood  heavy,  hard,  stiff,'  strong,  of 
rather  coarse  texture,  white  to  light  brown,  not  dura- 
ble in  the  ground,  and  subject  to  the  inroads  of 
boring-insects;  it  shrinks  and  checks  considerably 
in  drying,  works  and  stands  well,  and  takes  a  good 
polish.  Used  for  furniture,  in  turnery,  for  handles, 
lasts,  etc.  Abroad  it  is  very  extensively  employed 
by  the  carpenter,  millwright,  and  wagon-maker,  in 
turnery  as  well  as  wood-carving.  The  beech  is  a 
medium-sized  tree,  common,  sometimes  forming  for- 
ests; most  abundant  in  the  Ohio  and  the  Mississippi 
basin,  but  found  from  Maine  to  Wisconsin  and 
southward  to  Florida. 

233.  "Birch. — Wood  heavy,  hard,  strong,  of  fine  texture  ;  sap  wood  whit- 
ish, heartwood  in  shades  of  brown  with  red  and  yellow;  very  handsome, 
with  satiny  lustre,  equalling  cherry.     The  wood  shrinks  considerably  in  dry- 
ing, works  and  stands  well  and  takes  a  good  polish,  but  is  not  durable  if 
exposed.     Birch  is  used  for  finishing-lumber  in  building,  in  the  manufac- 
ture of  furniture,  in  wood-turnery  for  spools,  boxes,  wooden  shoes,  etc.,  for 
shoe  lasts  and  pegs,  for  wagon-hubs,  ox-yokes,  etc.,  also  in  wood-carving. 
The  birches  are  medium-sized  trees,  form  extensive  forests  northward,  and 
occur  scattered  in  all  broad-leaved  forests  of  the  Eastern  United  States. 


FIG.  178.—^.  ferruginea. 


48.  CHERRY-BIRCH  (Betula  lento)  (black  birch, 
sweet  birch,  mahogany-birch):  Medium-sized  tree; 
very  common.  Maine  to  Michigan  and  to  Tennessee. 


FIG.  179.—  B.  lentd. 

49.  YELLOW  BIRCH  (Betula  luted)  (gray 
birch):  Medium-sized  tree;  common.  Maine  to 
Minnesota  and  southwest  to  Tennessee. 


T    ¥/ 

FIG.  180.—  B.  lutea. 


TIMBER. 


283 


50.  RED  BIRCH  (Betula  nigra)  (river-birch): 
Small  to  medium-sized  tree;  very  common;  lighter 
and  less  valuable  than  the  preceding.  New  England 
to  Texas  and  Missouri 


XJU, 

Fm.  181.—  B.  nigra. 

51.  CANOE-BIRCH  (Betula  papyri/era)  (white 
birch,  paper-birch) :  Generally  a  small  tree;  common, 
forming  forests;  wood  of  good  quality,  but  relatively 
light.  All  along  the  northern  boundary  of  United 
States  and  northward,  from  the  Atlantic  to  the  Pacific. 


FIG.  182.— B.  papy- 
r  if  era. 

Black  Walnut.     See  WALNUT. 
234.  Blue  Beech. 

52.  BLUE  BEECH  (Carpinus caroliniana)  (horn- 
beam, water-beech,  ironwood) :  Wood  very  heavy, 
hard,  strong,  very  stiff,  of  rather  fine  texture  and 
white  color;  not  durable  in  the  ground;  shrinks 
und  checks  greatly,  but  works  and  stands  well. 
Used  chiefly  in  turnery  for  tool-handles,  etc. 
Abroad  much  used  by  millwrights  and  wheel- 
wrights. A  small  tree,  largest  in  the  Southwest, 
but  found  in  nearly  all  parts  of  the  Eastern  United 
States. 


FIG.  183.— (7.  caroliniana. 


Bois  d'Arc.     See  OSAGE  ORANGE. 

235.  Buckeye— Horse-Chestnut. — Wood  light,  soft,  not  strong,  often 
quite  tough,  of  fine  and  uniform  texture  and  creamy-white  color.  It  shrinks 
considerably,  but  works  and  stands  well.  Used  for  wooden  ware,  artificial 
limbs,  paper-pulp,  and  locally  also  for  building-lumber.  Small-sized  trees, 
scattered. 


284 


THE  MATERIALS  OF  CONSTRUCTION. 


53.  OHIO  BUCKEYE  (JSsculus  glabra)  (fetid  buckeye) 
Alleghanies,  Pennsylvania  to  Indian  Territory. 


FIG  184. 
E.  glabra. 


54.  SWEET  BUCKEYE   (^Esculus  flava):  Alle- 
ghanies, Pennsylvania  to  Texas. 


236.  Butternut. 


FIG.  1SQ.—J.  tinerea. 
237.  Catalpa. 


FIG  185.— ^0.  flaxa. 


55.  BUTTERNUT  (Juglans  cinerea)  (white 
walnut):  Wood  very  similar  to  black  walnut, 
but  light,  quite  soft,  not  strong,  and  of  light- 
brown  color.  Used  chiefly  for  finishing  lumber, 
cabinetwork,  and  cooperage.  Medium-sized 
tree,  largest  and  most  common  in  the  Ohio 
basin;  Maine  to  Minnesota  and  southward  to 
Georgia  and  Alabama. 


56.  CATALPA  (Catalpa  speciosa):  Wood  light,, 
soft,  not  strong,  brittle,  durable,  of  coarse  texture 
and  brown  color;  used  forties  and  posts,  but  well 
suited  for  a  great  variety  of  uses.  Medium-sized 
trees;  lower  basin  of  the  Ohio  Eiver,  locally  com- 
mon. Extensively  planted,  and  therefore  promising 
to  become  of  some  importance. 


FIG.  187.— C.  speciosa. 


TIMBER. 


285 


238.  Cherry. 

57.  CHERRY  (Prunus  serotina) :  Wood  heavy,  hard,  strong,  of  fine  tex- 
ture; sapwood 'yellowish  white,  heartwood  reddish  to  brown.  The  wood 
shrinks  considerably  in  drying,  works  and  stands  well,  takes  a  good  polish, 
and  is  much  esteemed  for  its  beauty.  Cherry  is 
chiefly  used  as  a  decorative  finishing-lumber  for 
buildings,  cars,  and  boats,  also  for  furniture  and  in 
turnery.  It  is  becoming  too  costly  for  many  ^purposes 
for  which  it  is  naturally  well  suited.  The  lumber- 
furnishing  cherry  of  this  country,  the  wild  black 
cherry  (Prunus  serotina),  is  a  small  to  medium-sized 
tree,  scattered  through  many  of  the  broad-leaved 
woods  of  the  western  slope  of  the  Alleghanies,  but  FlG-  188-~ p-  8e™tina. 
found  from  Michigan  to  Florida  and  west  to  Texas.  Other  species  of  this 
genus  as  well  as  the  hawthorns  (Cratcegas)  and  wild  apple  (Pyrus]  are  not 
commonly  offered  in  the  market.  Their  wood  is  of  the  same  character  as 
cherry,  often  even  finer,  but  in  small  dimensions. 


239.  Chestnut. 


FIG.  189.— a  vulgaris. 


58.  CHESTXUT  (Castanea  vulgaris  var.  ameri- 
cana) :  Wood  light,  moderately  soft,  stiff,  not  strong, 
of  coarse  texture;  the  sapwood  light,  the  heartwood 
darker  brown.  It  shrinks  and  checks  considerably 
in  drying,  works  easily,  stands  well,  and  is  very  dura- 
ble. Used  in  cabinetwork,  cooperage,  for  railway-ties, 
telegraph-poles,  and  locally  in  heaVy  construction. 
Medium-sized  tree,  very  common  in  the  Alleghanies, 
occurs  from  Maine  to  Michigan  and  southward  to 
Alabama. 


59.  CHINQUAPIN  (Castanea  pumila):  A  small-sized 
tree,  with  wood  slightly  heavier  than,  but  otherwise  sim- 
ilar to,  the  preceding;  most  common  in  Arkansas,  but 
with  nearly  the  same  range  as  the  chestnut. 


FIG.  190.  —  C.  pumila. 


286 


THE  MATERIALS  OF  CONSTRUCTION. 


60.  CHINQUAPIN  ( Castanopsis  chryso- 
pliylld] :  A  medium-sized  tree  of  the  west- 
ern ranges  of  California  and  Oregon. 


240.  Coffee-tree. 


FIG.  191.— C.  chrysophylla. 

61.  COFFEE-TREE  (Gymnodadus  oanadensis) 
(coffee-nut) :  Wood  heavy,  hard,  strong,  very  stiff,  of 
coarse  texture;  durable;  the  sapwood  yellow,  the 
heartwood  reddish  brown;  shrinks  and  checks  con- 
siderably in  drying;  works  and  stands  well  and  takes 
a  good  polish.  It  is  used  to  a  limited  extent  in  cab- 
inetwork. A  medium  to  large-sized  tree;  not  com- 
mon. Pennsylvania  to  Minnesota  and  Arkansas. 


FIG.  192. — G.  canadensis. 


Cottonwood.     See  POPLAR. 

Cucumber-tree.     See  TULIP. 

241.  Elm. — Wood  heavy,  hard,  strong,  very  tough:  moderately  durable  in 
contact  with  the  soil;  commonly  cross-grained,  difficult  to  split  and  shape, 
warps,  and  checks  considerably  in  drying,  but  stands  well  if  properly  han- 
dled. The  broad  sapwood  whitish,  heart  brown,  both  with  shades  of  gray 
and  red;  on  split  surface  rough;  texture  coarse  to  fine;  capable  of  high 
polish.  Elm  is  used  in  the  construction  of  cars,  wagons,  etc.,  in  boat-  and 
ship-building,  for  agricultural  implements  and  machinery;  in  rough  cooper- 
age, saddlery  and  harness  work,  but  particularly  in  the  manufacture  of  all 
kinds  of  furniture,  where  the  beautiful  figures,  especially  those  of  the  tan- 
gential or  bastard  section,  are  just  beginning  to  be  duly  appreciated.  The 
elms  are  medium  to  large-sized  trees,  of  fairly  rapid  growth,  with  stout  trunk, 
form  no  forests  of  pure  growth,  but  are  found  scattered  in  all  the  broad- 
leaved  woods  of  our  country,  sometimes  forming  a  considerable  portion  of 
the  arborescent  growth. 


TIMBER. 


287 


62.  WHITE-ELM  (Ulmus  americana)  (American 
elm,  water-elm) :  Medium  to  large-sized  tree,  com- 
mon. Maine  to  Minnesota,  southward  to  Florida 
and  Texas. 


FIG.  193.—  U.  americana. 

63.  ROCK-ELM  (Ulmus  racemosa)  (cork-elm, 
hickory-elm,  white  elm,  cliff-elm) :  Medium  to  large- 
sized  tree.  Michigan,  Ohio,  from  Vermont  to  Iowa, 
southward  to  Kentucky. 


FIG.  194. —  U.  racemosa. 


64.  RED  ELM  (Ulmus  fulva)  (slippery  elm, 
moose-elm) :  Small-sized,  tree,  found  chiefly  along 
watercourses.  New  York  to  Minnesota,  and  south- 
ward to  Florida  and  Texas. 


FIG.  195.—  U.  fulva. 


65.  CEDAR-ELM  ( Ulmus  crassifolia] : 
Small-sized  tree,  quite  common.  Arkansas 
and  Texas. 


FIG.  196.—  U.  crassifolia. 


288 


THE  MATERIALS  OF  CONSTRUCTION. 


66.  WINGED  ELM  (Ulmus  alata)  (Wahoo): 
Small-sized  tree,  locally  quite  common.  Arkan- 
sas, Missouri,  and  eastern  Virginia. 


FIG.  197.—  U.  alata. 

242.  Gum. — This  general  term  refers  to  two  kinds  of  wood  usually  dis- 
tinguished as  sweet  or  red  gum,  and  sour,  black,  or  tupelo  gum,  the  former 
being  a  relative  of  the  witch-hazel,  the  latter  belonging  to  the  dogwood 
family.  » 


ica. 


67.  TUPELO  (Nyssa  sylvatica)  (sour  gum,  black 
gum) :  Maine  to  Michigan,  and  southward  to  Flor- 
ida and  Texas.  Wood  heavy,  hard,  strong,  tough, 
of  fine  texture,  frequently  cross-grained,  of  yellowish 
or  grayish-white  color,  hard  to  split  and  work, 
troublesome  in  seasoning,  warps  and  checks  consid- 
erably, and  is  not  durable  if  exposed;  used  for  wagon- 
hubs,  wooden  ware,  handles,  wooden  shoes,  etc. 
Medium  to  large-sized  trees,  with  straight,  clear 
trunks;  locally  quite  abundant,  but  never  forming 
forests  of  pure  growth. 


68.  TUPELO  GUM  (Nyssa  uniflora)  (cotton- 
gum)  :  Lower  Mississippi  basin,  northward  to  Illi- 
nois and  eastward  to  Virginia;  otherwise  like  pre- 
ceding species. 


FIG.  199.—  N.  uniflora. 


TIMBER. 


289 


69.  SWEET   GUM   (Liquidambar  styraciflua)  (red  gum,  liquidambar, 

bilsted) :  Wood  rather  heavy,  rather  soft,  quite  stiff 
and  strong,  tough,  commonly  cross-grained,  of  fine 
texture;  the  broad  sapwood  whitish,  the  heart- 
wood  reddish  brown;  the  wood  shrinks  and  warps 
considerably,  but  does  not  check  badly,  stands  well 
when  fully  seasoned,  and  takes  good  polish.  Sweet 
gum  is  used  in  carpentry,  in  the  manufacture  of  fur- 
niture, for  cut  veneer,  for  wooden  plates,  plaques, 
baskets,  etc.,  also  for  wagon-hubs,  hat-blocks,  etc. 
A  large-sized  tree,  very  abundant,  often  the  princi- 
pal tree  in  the  swampy  parts  of  the  bottoms  of  the 

FIG.  200.—  L.  styraciflua.      Lower  Mississippi  Valley;  occurs  from  New  York 

to  Texas,  and  from  Indiana  to  Florida. 

243.  Hackberry. 

70.  HACKBERRY  (Cettis occidentalis)  (sugar-berry): 
The  handsome  wood  heavy,  hard,  strong,  quite  tough, 
of  moderately  fine  texture,  and  greenish-  or  yellowish- 
white  color;  shrinks  moderately,  works  well,  and  takes 
a  good  polish.     So  far  but  little  used  in  the  manufac- 
ture of  furniture.     Medium  to  large-sized  tree,  locally 
quite  common,  largest  in  the  Lower  Mississippi  Valley; 
occurs  in  nearly  all  parts  of  the  Eastern  United  States. 

244.  Hickory. — Wood  very  heavy,  hard,  and  strong,  proverbially  tough, 
of  rather  coarse  texture,  smooth  and  of  straight  grain.     The  broad  sapwood 
white,  the   heart  reddish  nut-brown.     It  dries  slowly,  shrinks  and  checks 
considerably;  is  not  durable  in  the  ground,  or  if  exposed,  and  especially  the 
sapwood,  is  always  subject  to  the  inroads  of  boring-insects..    Hickory  excels 
as  carriage  and  wagon  stock,  but  is  also  extensively  used  in  the  manufacture 
of  implements  and  machinery,  for  tool-handles,  timber-pins,  for   harness 
work  and  cooperage.     The  hickories  are  tall  trees  with  slender  stems,  never 
form  forests,  occasionally  small  grove's,  but  usually  occur  scattered  among 
other   broad-leaved  trees  in  suitable  localities.     The  following  species  all 
contribute  more  or  less  to  the  hickory  of  the  markets: 


71.  SHAGBARK  HICKORY  (Hicoria  ovata)  (shell- 
bark  hickory) :  A  medium  to  large-sized  tree,  quite 
common;  the  favorite  among  hickories;  best  devel- 
oped in  the  Ohio  and  Mississippi  basins ;  from  Lake 
Ontario  to  Texas,  Minnesota  to  Florida. 


FIG.  201.— G.  occiden- 
talis. 


FIG  202.—  H.  ovata. 


290 


THE  MATERIALS  OF  CONSTRUCTION. 


77.  MOCKERNUT  HICKORY  (Hicoria  alia)  (black 
hickory,  bull- and  black-nut,  big-bud,  and  white-heart 
hickory):  A  medium  to  large-sized  tree,  with  the  same 
range  as  the  foregoing;  common,  especially  in  the 
South. 


FIG.  203.—  H  alba. 

73.  PIGNUT  HICKORY  (Hicoria  glair  a) 
(brown  hickory,  black  hickory,  switch-bud  hick- 
ory):  Medium  to  large-sized  tree,  abundant;  all 
Eastern  United  States. 


FIG.  204.— H.  glabra. 


74.  BITTER-NUT  HICKORY  (Hicoria  minima) 
(swamp  hickory) :  A  medium-sized  tree,  favoring 
wet  localities,  with  the  same  range  as  the  preceding. 


FIG.  205.—  H.  minima 


75.  PECAN  (Hicoria  pecan)  (Illinois  nut):  A 
large  tree,  very  common  in  the  fertile  bottoms  of  the 
Western  streams.  Indiana  to  Nebraska  and  south- 
ward to  Louisana  and  Texas. 


FIG.  206.— //.  pecan. 


TIMBER. 


291 


245.  Holly. 


FIG.  207.— I.  opaca. 


76.  HOLLY  (Ilex  opaca):  Wood  of  medium  weight,, 
hard,  strong,  tough,  of  fine  texture  and  white  color; 
works  and  stands  well,  used  for  cabinetwork  and  turnery. 
A  small  tree,  most  abundant  in  the  Lower  Mississippi 
Valley  and  Gulf  States,  but  occurring  eastward  to  Massa- 
chusetts and  north  to  Indiana. 


Horse-chestnut.     See  BUCKEYE. 
Ironwood.     See  BLUE  BEECH. 

246.  Locust. — This  name  applies  to  both  of  the  following: 

77.  BLACK  LOCUST  (Robinia  pseudacacia)  (black  locust,  yellow  locust) : 

Wood  very  heavy,  hard,  strong,  and  tough,  of 
coarse  texture,  very  durable  in  contact  with  the 
soil,  shrinks  considerably,  and  suffers  in  season- 
ing; the  very  narrow  sapwood  yellowish,  the 
heartwood  brown,  with  shades  of  red  and  green. 
Used  for  wagon-hubs,  treenails  or  pins,  but  espe- 
cially for  ties,  posts,  etc.  Abroad  it  is  much  used 
for-  furniture  and  farm-implements,  and  also  in 
turnery.  Small  to  medium-sized  tree,  at  home  in 
the  Alleghanies,  extensively  planted,  especially 

in  the  West. 
FIG.  208.  —R.  pseudacacia. 

78.  HONEY-LOCUST      (Gleditschia     triacantlws) 
(black  locust,  sweet   locust,  three-thorned   acacia) : 
Wood  heavy,  hard,  strong,  tough,  of  coarse  texture, 
susceptible  of  a  good  polish,  the  narrow  sapwood  yel- 
low, the  heartwood  brownish  red.     So  far  but  little 
appreciated  except  for  fencing  and  fuel;  used  to  some 
extent  for  wagon-hubs  and  in  rough   construction. 

A  medium-sized  tree,  found  from   Pennsylvania  to   «*^     5" 

Nebraska,  and  southward  to  Florida  and  Texas;  lo-  FIG.  209. — G.  triacanthos. 

cally  quite  abundant. 

Magnolia.     See  TULIP. 

247.  Maple. — Wood  heavy,  hard,  strong,  stiff,  and  tough,  of  fine  texture,, 
frequently  wavy-grained,  this  giving  rise  to  "  curly  "  and  "  blister"  figures; 
not  durable  in  the  ground  or  otherwise  exposed.     Maple  is  creamy  white, 
with  shades  of  light  brown  in  the  heart;  shrinks  moderately,  seasons,  works 
and  stands  well,  wears  smoothly,  and  takes  a  fine  polish.     The  wood  is  used 
for  ceiling,  flooring,  panelling,  stairway,  arid  other  finishing-lumber  in  house, 
ship,  and  car  construction;  it  is  used  for  the  keels  of  boats  and  ships,  in  the 
manufacture  of  implements  and  machinery,  but  especially  for  furniture, 
where  entire  chamber  sets  of  maple  rival  those  of  oak.     Maple  is  also  used 


S92 


THE  MATERIALS  OF  CONSTRUCTION. 


for  shoe-lasts  and  other  form-blocks,  for  shoe-pegs,  for  piano  actions,  school 
•apparatus,  for  wood  type  in  show-bill  printing,  tool-handles,  in  wood-carv- 
ing, turnery,  arid  scrollwork.  The  maples  are  medium-sized  trees,  of  fairly 
rapid  growth;  sometimes  form  forests  and  frequently  constitute  a  large  pro- 
portion of  the  arborescent  growth. 


79.  SUGAR-MAPLE  (Acer  saccharum)  (hard 
maple,  rock-maple) :  Medium  to  large-sized  tree, 
very  common,  forms  considerable  forests.  Maine 
to  Minnesota,  abundant,  with  birch,  in  parts  of 
the  pineries;  southward  to  northern  Florida; 
most  abundant  in  the  region  of  the  Great  Lakes. 


FIG.  210. — A.  saccharum. 


80.  RED  MAPLE  (Acer  rubrum)  (swamp-  or  water- 
maple)  :  Medium-sized  tree.  Like  the  preceding,  but 
scattered  along  watercourses  and  other  moist  localities. 


FIG.  211. — A.  rubrum. 

81.  SILVER  MAPLE  (Acer  saccliarinum)  (soft 
maple,  silver  maple):  Medium-sized,  common;  wood 
lighter,  softer,  inferior  to  hard  maple,  and  usually 
offered  in  small  quantities  and  held  separate  in  the 
market.  Valley  of  the  Ohio,  but  occurs  from  Maine 
o  Dakota,  and  southward  to  Florida. 


FIG.    212.—  A.   sacchari- 
num. 


82.  BROAD-LEAVED  MAPLE  (Acer  macropliyl- 
lum):  Medium-sized  tree,  forms  considerable 
forests,  and  like  the  preceding  has  a  lighter, 
softer,  and  less  valuable  wood.  Pacific  Coast. 


PIG.  213. — A.  macrophyllum. 


TIMBER. 


293 


248.  Mulberry. 

83.  RED  MULBERRY  (Morus  rubra):  Wood  moderately 
heavy,  hard,  strong,  rather  tough,  of  coarse  texture,  dur- 
able; sapwood  whitish,  hard  yellow  to  orange-brown; 
shrinks  and  checks  considerably  in  drying;  works  and 
stands  well.  Used  in  cooperage  and  locally  in  ship-build- 
ing and  in  the  manufacture  of  farm-implements.  A  small- 


sized  tree,  common  in  the  Ohio  and   Mississippi  valleys,    FIG  gl4  _M 


but  widely  distributed  in  the  Eastern  United  States.  bra 

249.  Oak. — Wood  very  variable,  usually  very  heavy  and  hard,  very  strong- 
and  tough,  porous,  and  of  coarse  texture;  the  sapwood  whitish,  the  heart 
"  oak  "  brown  to  reddish  brown.  It  shrinks  and  checks  badly,  giving  trouble 
in  seasoning,  but  stands  well,  is  durable,  and  little  subject  to  attacks  of  in- 
sects. Oak  is  used  for  many  purposes:  in  ship-building,  for  heavy  construc- 
tion, in  common  carpentry,  in  furniture,  car,  and  wagon  work,  cooperage, 
turnery,  and  even  in  wood-carving;  also  in  the  manufacture  of  all  kinds  of 
farm-implements,  wooden  mill  machinery,  for  piles  and  wharves,  railway- 
ties,  etc.  The  oaks  are  medium  to  large-sized  trees,  forming  the  predomi- 
nant part  of  a  large  portion  of  our  broad-leaved  forests,  so  that  these  are 
.generally  "  oak  forests,"  though  they  always  contain  a  considerable  propor- 
tion of  other  kinds  of  trees.  Three  well-marked  kinds,  white,  red,  and  live 
oak,  are  distinguished  and  kept  separate  in  the  market,  Of  the  two  princi- 
pal kinds  white  oak  is  the  stronger,  tougher,  less  porous,  and  more  durable. 
Ked  oak  is  usually  of  coarser  texture,  more  porous,  often  brittle,  less  dura- 
ble, and  even  more  troublesome  in  seasoning  than  white  oak.  In  carpen- 
try and  furniture  work  red  oak  brings  about  the  same  price  at  present  as 
white  oak.  The  red  oaks  everywhere  accompany  the  white  oaks,  and,  like 
the  latter,  are  usually  represented  by  several  species  in  any  given  locality. 
Live-oak,  once  largely  employed  in  ship-building,  possesses  all  the  good 
qualities  (except  that  of  size)  of  white  oak  even  to  a  greater  degree.  It  is 
one  of  the  heaviest,  hardest,  and  most  desirable  building-timbers  of  this 
country;  in  structure  it  resembles  the  red  oaks,  but  is  much  less  porous. 


84.  WHITE  OAK  (Quercus  alba):  Medium  to 
large-sized  tree,  common  in  the  Eastern  States, 
Ohio  and  Mississippi  valleys;  occurs  throughout 
Eastern  United  States. 


FIG.  215.— .  alba. 


294 


THE  MATERIALS  OF  CONSTRUCTION. 


85.  BUR -OAK  (Quercus  macrocarpa) 
(mossy-cup  oak,  over-cup  oak):  Large-sized 
tree,  locally  abundant,  common.  Bottoms 
west  of  Mississippi;  range  farther  west  than 
preceding. 


FIG.  216.  —  Q  macrocarpa. 

86.  SWAMP  WHITE  OAK  (Quercus  bicolor): 
Large-sized  tree,  common.  Most  abundant  in  the 
Lake  States,  but  with  range  as  in  white  oak. 


FIG.  217. — Q.  bicolor. 

87.  YELLOW  OAK  (Quercus  prinoides)  (chestnut-oak,  chin- 
quapin oak) :  Medium-sized  tree.     Southern  Alleghanies,  east-   g- 
ward  to  Massachusetts. 

FIG.  218. 
Q.  prinoides. 


88.  BASKET-OAK  (Quercus  michauxii)  (cow- 
oak):  Large-sized  tree,  locally  abundant;  lower 
Mississippi  and  eastward  to  Delaware. 


FIG.  219.— Q.  michauxii. 


89.  OVER-CUT  OAK  (Quercus  lyrata)  (swamp  white 
oak,  swamp  post-oak):  Medium  to  large-sized  tree, 
rather  restricted;  ranges  as  in  the  preceding. 


FIG.  220.  —  Q.  lyrata. 


TIMBER. 


295 


90.  POST-OAK  (Quercus  obtusilola)  (iron- 
oak):  Medium  to  large-sized  tree.  Arkansas 
to  Texas,  eastward  to  New  England,  and 
northward  to  Michigan. 


FIG.  221.— Q.  oUmiloba. 


91.  WHITE   OAK  (Quercus   durandii):    Medium  to 
small-sized  tree.     Texas,  eastward  to  Alabama. 


FIG.    222.  —  Q.    du- 
randii. 


92.  WHITE  OAK  (Quercus  garryana):   Medium  to 
large-sized  tree.     Washington  to  California. 


FIG.  223.— Q. 
garryana. 


93.  WHITE   OAK  (Quercus  lobata):    Medium  to 
large-sized   tree;   largest  oak  on  the   Pacific  coast,    r 
California. 


FIG.  224,— Q.  lobata. 


296 


THE  MATERIALS  OF  CONSTRUCTION. 


94.  RED  OAK  (Quercus  rubra)  (black  oak): 
Medium  to  large-sized  tree;  common  in  all  parts  of 
its  range.  Maine  to  Minnesota,  and  southward  to 
the  Gulf. 


FIG.  225.—$.  rubra. 


95.  BLACK  OAK  (Quercus  tinctoria)  (yellow 
oak) :  Medium  to  large-sized  tree;  very  common  in 
the  Southern  States,  but  occurring  north  as  far  as 
Minnesota,  and  eastward  to  Maine. 


FIG.  226.  —  Q.  tinctoria. 


96.  SPANISH  OAK  (Quercus falcata)  (red  oak): 
Medium-sized  tree;  common  in  the  South  Atlantic 
and  Gulf  region,  but  found  from  Texas  to  New 
York,  and  north  to  Missouri  and  Kentucky. 


FIG.  227.— Q.  falcata. 


97.  SCARLET  OAK  (Quercus  coccinea):  Me- 
dium to  large-sized  tree;  best  developed  in  the 
lower  basin  of  the  Ohio,  but  found  from  Maine 
to  Missouri,  and  from  Minnesota  to  Florida. 


FIG.  228.  —  Q.  coccinea, 

98.  PIN-OAK  (Quercus  palustris]  (swamp  Spanish 
oak,  water-oak):  Medium  to  large-sized  tree,  common 
along  borders  of  streams  and  swamps.  Arkansas  to  Wis- 
consin, and  eastward  to  the  Alleghanies. 


FIG.  229.—$.  palus- 
iris. 


TIMBER 


297 


99.  WILLOW-OAK  (Quercus  pliellos)  (peach-oak): 
Small  to  medium-sized  tree.  New  York  to  Texas, 
and  northward  to  Kentucky. 


Q.  phellos. 


100.  WATER-OAK  (Quercus  aquatica)  (duck-oak, 
possum-oak,  punk-oak) :  Medium  to  large-sized  tree, 
of  extremely  rapid  growth.  Eastern  Gulf  States,  east- 
ward to  Delaware,  and  northward  to  Missouri  and 
Kentucky. 


FIG.  231.  —  Q.  aquatica. 


101.  LIVE-OAK  (Quercus  virens):  Small-sized  tree, 
scattered  along  the  coast  from  Virginia  to  Texas. 


FIG.  232.— Q.  virens. 


102.  LIVE-OAK  (Quercus 
cJirysolepis]  (m  a  u  l-o  a  k, 
Valparaiso  oak):  Medium- 
sized  tree.  California. 


FIG.  233. —Q.  cJirysolepis. 


298 


THE  MATERIALS  OF  CONSTRUCTION. 


250.  Osage  Orange. 

103.  OSAGE  ORAXGE  (Madura  aurantiacd)  (Bois  d'Arc):  Wood  very 
heavy,  exceedingly  hard,  strong,  not  tough,  of 
moderately  coarse  texture,  and  very  durable;  sap- 
wood  yellow,  heart  brown  on  the  end,  yellow  on 
longitudinal  faces,  soon  turning  grayish  brown  if 
exposed;  it  shrinks  considerably  in  drying,  but 
once  dry  it  stands  unusually  well.  Formerly  much 
used  for  wheel  stock  in  the  dry  regions  of  Texas; 
otherwise  employed  for  posts,  railway-ties,  etc. 
Seems  too  little  appreciated ;  it  is  well  suited  for 
turned  ware  and  especially  for  wood-carving.  A 
small-sized  tree,  of  fairly  rapid  growth,  scattered 
through  the  rich  bottoms  of  Arkansas  and  Texas. 

251.  Persimmon. 


FIG.  234. — M.  aurantiaca 


104,  PERSIHMOK  (Diospyros  virginiana) :  Wood 
very  heavy  and  hard,  strong  and  tough;  resembles 
hickory,  but  is  of  finer  texture;  the  broad  sapwood 
cream-color,  the  heart  black;  used  in  turnery  for 
shuttles,  plane-stocks,  shoe-lasts,  etc.  Small  to 
medium-sized  tree,  common  and  best  developed  in 
the  Lower  Ohio  Valley,  but  occurs  from  New  York 
to  Texas  and  Missouri. 


FIG.  235. — D.  virginiana, 

252.  Poplar  and  Cottonwood.  (See  also  TULIP-WOOD.) — Wood  light, 
very  soft,  not  strong,  of  fine  texture  and  whitish,  grayish,  to  yellowish  color, 
usually  with  a  satiny  lustre.  The  wood  shrinks  moderately  (some  cross- 
grained  forms  warp  excessively),  but  checks  little;  is  easily  worked,  but  is 
not  durable.  Used  as  building-  and  furniture-lumber,  in  cooperage  for 
sugar-  and  flour-barrels,  for  crates  and  boxes  (especially  cracker-boxes),  for 
woodenware  and  paper-pulp. 


105.  COTTONWOOD  (Populuo  monilifera):  Large- 
sized  tree;  forms  considerable  forests  along  many  of 
the  Western  streams,  and  furnishes  most  of  the 
cottonwood  of  the  market.  Mississippi  Valley  and 
west;  New  England  to  the  Rocky  Mountains. 


FIG.  236.— P.  monilifera. 


TIMBER. 


299 


106.  BALSAM  (Populus  balsamifera)  (balm  of 
Gilead):  Medium  to  large-sized  tree;  common  all 
along  the  northern  boundary  of  the  United  States. 


FIG.  237.— P.  balsamifera. 

107.  BLACK  COTTON-WOOD  (Populus  trichocarpa)  \ 
The  largest  deciduous  tree  of  Washington ;  very  common. 
Northern  Rocky  Mountains  and  Pacific  region. 


FIG.  238. 
P.  trichocarpa. 

108.  COTTONWOOD  (Populus  fre- 
montii  var.  ivislizeni) :  Medium  to  large- 
sized  tree,  common.  Texas  to  Cali- 
fornia. 


FIG.  239.— P.  wislizeni. 


109.  POPLAR  (Populus  grandidentata) :  Medium- 
sized  tree,  chiefly  used  for  pulp.  Maine  to  Minne- 
sota and  southward  along  the  Alleghanies. 


FIG.  240. 
P.  grandidentata. 


300 


THE  MATERIALS  OF  CONSTRUCTION. 


110.  ASPEX  (Populus  tremuloides):  Small  to 
medium-sized  tree,  often  forming  extensive  forests 
and  covering  burned  areas.  Maine  to  Washington 
and 
California  and  New  Mexico. 

See  GUM. 

See  GUM. 


th  ward,  south  in  the  Western  mountains  to 


FIG.  242. — 8.  sassafras. 


FIG   241 
P.  tremuloides. 
Sour  Gum. 
Red  Gum. 

253.  Sassafras. 

111.  SASSAFRAS   (Sassafras  sassafras):   Wood 
light,  soft,  not   strong,  brittle,  of   coarse   texture, 
durable;    sapwood    yellow,    heart    orange  -  brown. 
Used     in     cooperage,     for     skiffs,     fencing,     etc. 
Medium-sized  tree,  largest  in  the  Lower  Mississippi 
Valley,   from    New   England    to  Texas,  and   from 
Michigan  to  Florida. 

Sweet  Gum.     See  GUM. 

254.  Sycamore. 

112.  SYCAMORE  (Platanus  occidentalis}  (button-wood,  buttonball-tree, 

water-beech)  :  Wood  moderately  heavy,  quite  hard, 
stiff,  strong,  tough,  usually  cross-grained,  of  coarse 
texture,  and  white  to  light-brown  color;  the  wood 
is  hard  to  split  and  work,  shrinks  moderately, 
warps  and  checks  considerably,  but  stands  well. 
It  is  used  extensively  for  drawers,  backs,  bottoms, 
etc.,  in  cabinetwork,  for  tobacco-boxes,  in  cooper- 
age, and  also  for  finishing  lumber,  where  it  has 
too  long  been  underrated.  A  large  tree,  of  rapid 
growth,  common  and  largest  in  the  Ohio  and  Mis- 
sissippi valleys,  at  home  in  nearly  all  parts  of  the 

Eastern  United  States.     The  California  species  — 
FIG.  243.  —  P.  occidentalis.  -,10     rtl    ,  ... 

113.  Platanus    racemosa  —  resembles    in    its 

wood  the  Eastern  form. 

255.  Tulip-wood. 

114.  TULIP  -  TREE  (Liriodendron  tulipifera) 
(yellow  poplar,  white  wood)  :  Wood  quite  varia- 
ble in  weight,  usually  light,  soft,  stiff  but  not 
strong,  of  fine  texture  and  yellowish  color;  the 
wood  shrinks  considerably,  but  seasons  without 
much  injury;  works  and  stands  remarkably  well. 
Used  for  siding,  for  panelling  and  finishing-lum- 
ber in  house-,  car-,  and  ship-building,  for  side- 
boards and  panels  of  wagons  and  carriages;  also 
in  the  manufacture  of  furniture,  implements,  and 
machinery,  for  pump-logs,  and  almost  every  kind 


FIG.  244.— L.  tulipifera. 


TIMBER. 


301 


of  common  wooden  ware,  boxes,  shelving,  drawers,  etc.  An  ideal  wood  for 
the  carver  and  toyman.  A  large  tree,  does  not  form  forests,  but  is  quite 
common,  especially  in  the  Ohio  Basin;  occurs  from  New  England  to 
Missouri  and  southward  to  Florida. 


115.  CUCUMBER  -  TREE  (Magnolia  acumi- 
nata) :  A  medium-sized  tree,  most  common  in 
the  southern  Alleghanies,  but  distributed  from 
New  York  to  Arkansas,  southward  to  Alabama, 
and  northward  to  Illinois.  Resembling,  and 
probably  confounded  with,  tulip-wood  in  the 
markets. 


FIG.  245. — M.  acuminata. 


Tupelo.     See  GUM. 
256.  Walnut. 

116.  BLACK  WALNUT  (Juglans  nigra):  Wood  heavy,  hard,  strong,  of 
coarse  texture;  the  narrow  sapwood  whitish,  the 
heartwood  chocolate-brown.  The  wood  shrinks 
moderately  in  drying,  works  and  stands  well, 
takes  a  good  polish,  is  quite  handsome,  and  has 
been  for  a  long  time  the  favorite  cabinet-wood  in 
this  country.  Walnut,  formerly  used  even  for 
fencing,  has  become  too  costly  for  ordinary  uses, 
and  is  to-day  employed  largely  as  a  veneer,  for 
inside  finish  and  cabinetwork;  also  in  turnery,  for 
gunstocks,  etc.  Black  walnut  is  a  large  tree,  with 
stout  trunk,  of  rapid  growth,  and  was  formerly 
quite  abundant  throughout  the  Alleghany  region, 
occurring  from  New  England  to  Texas,  and  from 
Michigan  to  Florida. 

White  Walnut.     See  BUTTERNUT 

White  Wood.     See  TULIP,  and  also  BASSWOOD. 

Yellow  Poplar.     See  TULIP. 


FIG.  246. 


nigra. 


PART  III. 

TESTING-MACHINES   AND    METHODS    OF    TESTING 
MATERIALS   OF  CONSTRUCTION. 


CHAPTER   XIV. 
MECHANICAL  TESTS  IN  GENERAL. 

257.  General  Observations. — Mechanical  tests  are  those  most  commonly 
used  to  discover  the  working  qualities  of  the  materials  of  construction. 
Since  these  materials  nearly  always  have  to  resist  the  action  of  external 
forces,  it  follows  that  the  suitableness  of  such  a  material  to  resist  the  action 
of  these  forces  is  best  determined  by  tests  approximating  as  nearly  as  may 
be  to  the  conditions  of  actual  practice. 

Mechanical  tests,  therefore,  are  of  supreme  importance  in  the  study  of 
any  building  material.  By  standardizing  the  conditions  under  which  these 
tests  are  carried  out,  the  results  become  comparable  wherever  or  by  whom- 
soever they  are  made,  and  they  also  become  authoritative  in  all  countries 
and  for  all  purposes.  If  such  results  can  be  made  wholly  independent  of 
the  means  employed  in  making  the  tests,  and  hence  to  furnish  a  knowledge 
of  the  true  characteristics  of  the  material,  they  can  be  used  safely  in  theo- 
retical generalizations  on  the  one  hand,  and  in  the  practical  designing  of 
structures  on  the  other.  With  many  kinds  of  tests  this  ideal  divorcement 
of  the  results  from  the  conditions  of  the  tests  can  certainly  never  be 
attained,  as  in  the  case  of  tests  by  impact,  but  it  doubtless  can  be  practically 
attained  in  some  of  the  more  simple  tests,  as  in  tension  and  compression. 
In  the  former  case  the  most  that  can  be  accomplished  is  to  prescribe  uniform 
conditions  in  order  that  the  results  obtained  by  different  experimenters  may 
be  comparable,  although  they  may  not  serve  for  accurate  scientific  general- 
izations. They  might  also  serve  to  give  a  relative  value  to  the  various 
materials  or  samples  so  tested,  and  to  grade  them  with  some  degree  of  ap- 
proximation to  their  true  relative  merits  for  a  proposed  purpose.  Such 
tests,  therefore,  may  serve  fully  their  immediate  object  even  though  the 

302 


MECHANICAL  TESTS  IN  GENERAL.  303 

results  can  be  given  no  absolute  significance  whatever.  If,  however,  the 
conditions  of  such  tests  are  allowed  to  vary,  they  would  lose  even  this  rela- 
tive significance,  and  would  therefore  be  quite  worthless.  The  standardiz- 
ing of  any  particular  kind  of  test  evidently  depends  on  the  state  of  the  science 
at  the  time ;  and  as  our  knowledge  of  any  particular  property  of  a  material 
increases,  it  is  probable  that  our  standard  methods  of  testing  will  also  have 
to  change.  No  such  standards,  therefore,  can  be  fixed  permanently,  but 
certain  methods  can  be  agreed  on  and  followed  for  a  time,  and  when  a  change 
is  made  let  all  change  together.  To  attain  to  this  kind  of  unity  of  action 
it  is  necessary  to  have  a  world's  representative  body  which  will  command 
the  confidence  and  allegiance  of  both  the  theoretical  and  the  practical  users 
of  materials  in  all  civilized  countries  to  decide  such  questions.  A  beginning 
has  been  made  in  this  direction  in  the  International  Commission  on  the 
Standardization  of  Methods  of  Testing  the  Materials  of  Construction,  which 
has  had  several  meetings  in  Europe  at  intervals  of  about  three  years,  the 
last  one  being  at  Zurich  in  September,  1895,  where  a  permanent  organiza- 
tion was  effected.  The  French  Government,  also  (in  1891,  as  a  result  of 
action  taken  by  engineers  at  their  centennial  exposition  in  1889),  appointed 
a  national  French  Commission  of  over  one  hundred  of  the  leading  authorities 
in  France  to  report  on  this  subject.  Their  report,  printed  in  four  quarto 
volumes  (1895),  is  to-day  (1897)  by  far  the  best  single  source  of  information 
on  these  subjects.  They  have  proposed  what  appeared  to  them  practicable 
standard  tests  for  nearly  all  kinds  of  structural  materials. 

Evidently  no  complete  standardization  can  be  effected  for  tests  on  entire 
structural  forms,  since  these  vary  in  shape,  size,  and  disposition  of  parts, 
but  specimen  tests  can  be  standardized  since  all  significant  conditions  can  be 
made  uniform. 

258.  Mechanical  Tests  Classified. — In  a  general  way  we  may  divide 
mechanical  tests  of  building  materials  into  the  following  classes : 

With  reference  to  the  method  of  applying  the  loads  we  have — 

(1)  Static  Tests,  or  those  made  with  gradually  increasing  loads,  such  as 
the  ordinary  tests  in  tension,  compression,  cross-bending,  torsion,  and  shear- 
ing. 

(2)  Dynamic  Tests,  or  those  made  with  suddenly  applied  loads,  as  by  a 
falling  weight. 

(3)  Wearing  Tests,  or  those  made  for  determining  resistance  to  abrasion 
and  impact,  as  in  the  case  of  paving-materials. 

With  reference  to  the  character  of  the  test  specimen  we  have — 

(1)  Specimen    Tests,    or   those   made   upon  specimens  of  the   material 
specially  prepared  and  given  standard  forms  and  dimensions. 

(2)  Structural  Tests,  or  those  made  on  full-sized  structural  forms,  as 
bridge  members,  brick  piers,  pipes,  wire  ropes,  chains,  riveted  joints,  etc., 
or  on  the  structure  as  a  whole,  such  as  boilers,  simple  trusses,  frames,  and 
various  parts  of  machines. 

Complete  standard  rules  for  making  tests  of  structural  materials  can  be 


304  THE  MATERIALS  OF  CONSTRUCTION. 

adopted  for  making  all  kinds  of  tests  on  specially  prepared  specimens,  but 
they  can  be  only  partially  prescribed  for  tests  of  structural  forms. 

259.  General  Remarks  on  Testing-machines. — ffhe  following  considera- 
tions apply  to  testing-machines  and  testing-appliances  in  general  : 

1.  The  weighing  apparatus  should  be  quite  independent  of  the  loading 
apparatus,  the  former  usually  being  fixed  and  the  latter  movable. 

.  2.  In  lever  machines  the  length  of  the  knife-edges  must  be  proportioned 
to  the  maximum  loads  in  order  not  to  be  crushed  down,  and  they  should  be 
so  placed  that  all  will  receive  their  share  of  the  load.  They  must  also  be  so 
mounted  as  not  to  change  the  leverage  by  any  reaction  displacement  which 
may  occur  To  insure  this,  the  knife-edges  must  be  attached  to  the  levers, 
and  the  bearings  to  the  platform. 

3.  The  knife-edges  and  bearings  of  any  beam  must  lie  in  the  same 
straight  line,  and  this  line  should  lie  in  the  gravity  axis  of  the  beam  and  its 
rigid  attachments.     This  is  especially  necessary  for  the  weighing-beam  itself, 
so  that  its  vertical  angular  movement  may  not  disturb  the  counterbalancing. 
If  the  poise  is  moved  by  a  cord  over  a  pair  of  pulleys,  this  cord  should  be 
attached  to  the  poise-hanger  in  this  same  axial  line,  so  that  the  pulling  of 
the  poise  may  not  supply  a  leverage  on  the  beam  to  raise  or  lower  it. 

4.  Manometer  machines  have  many  peculiar  -errors.     For  example,  any 
air-bubble  in  the  indicating  liquid  vitiates  the  results  by  its  own  change  in 
volume  under  pressure.     Again,  the  exact  area  of  surface  subjected  to  pres- 
sure is  always  uncertain. 

5.  The  weighing  apparatus  should  be  so  constructed  as  to  be  readily 
verified  by  the  imposition  of  known  weights,  and  the  parts  should  be  open 
to  inspection  and  easily  repaired  and  kept  in  order. 

6.  A  precision  of  1  in'250  has  been  considered  sufficient.*     This  is  a 
proportional  error  of  0.4  of  1  per  cent. 

7.  The  loading  should  proceed  gradually  and  uniformly,  and  not  by 
sudden  increments  as  by  large  pump-pulsations,  or  by  the  adding  of  over- 
weights by  hand  to  the  weighing-beam.     The  rate  of  loading  should  also  be 
under  perfect  control. 

-•8.  The  machine  should  be  so  constructed  as  to  permit  the  free  use  of 
appliances  for  measuring  distortion  of  the  specimen  by  some  suitable  device. 

9.  If  used  for  compression  tests,  one  of  the  bearing-surfaces  should  be 
slightly  adjustable  to  accommodate  the  machine  to  the  non-parallel  faces  of 
the  test-block,  and  these  bearing-surfaces  should  be  harder  than  any  material 
tested  by  them.     The  neutral  axis  of  these  bearing-plates-  should  coincide 
with  the  axis  of  symmetry  of  the  applied  forces  as   transmitted  by  the 
machine  to  the  specimen.     For  these  tests  the  machine  should  have  a  very 
slow  movement. 

10.  If  used  for  cross-breaking  tests,  it  should  be  furnished  with  means  for 

the  deflection.     To  do  this  properly  a  rigid  connection  must  be 

*  This  standard  is  given  by  the  French  Commission. 


MECHANICAL  TESTS  IN  GENERAL.  305 

established  between  the  two  end  bearings  to  the  middle  bearing  (or  bear- 
ings), through  parts  not  under  stress,  in  order  that  the  loading  of  the 
specimen  may  not  disturb  this  rigid  relation. 

11.  Torsion  testing-machines  should  apply  the  torsion  movement  as  a 
true  couple  and  without  developing  any  tensile  or  bending  stress  in  the 
specimen. 

12.  Impact  testing-machines  should  as  far  as  possible  satisfy  the  condi- 
tions imposed  in  Art.  292.     That  is,  as  far  as  possible,  the  entire  energy  of 
the  blow  should  pass  into  the  specimen.     The  falling  weight  should  be  held 
to  its  course  either  by  vertical  guides,  in  the  case  of  a  falling  weight,  or  by 
n  pendulum  mounted  on  a  transverse  axis  resting  on  knife-edge  bearings. 
The  former  method  is  to  be  preferred.     The  falling  weight  should  be  sym- 
metrical in  form,  with  suitable  guiding  attachments,  to  be  formed  (cast)  in 
one  piece,  of  hard  metal,  with  its  centre  of  gravity  as  low  as  possible.     The 
height  of  the  weight  should  be  greater  than  the  width  between  the  guides, 
which  latter  should  be  quite  rigid,  true,  and  vertical,  and  should  offer  no 
frictional  resistance  to  the  falling  weight.     The  supporting  mass  should  be 
very  great  as  compared  to  that  of  the  falling  weight.     The  French  Commis- 
sion recommend  that  it  be  at  least  15  or  20  times  that  of  the  striking  body. 
Impact  tests  can  only  be  standardized  by  using  exactly  similar  appliances  in 
all  respects,  including  the  supporting  blocks  and  the  foundation  on  which 
these  supports  rest. 

260.  The  Effect  of  the  Rate  of  Loading  on  the  Results  of  the  Test, — The 
French  Commission  quote  M.  A.  Le  Chatelier  on  this  subject  as  follows: 
"  Metals  do  not  respond  instantly  to  the  deforming  action  of  external  forces. 
These  deformations,  both  elastic  and  permanent,  continue  to  increase  with 
time,  and  the  termination  of  the  instant  when  the  deformation  correspond- 
ing to  a  given  load  has  been  fully  completed  depends  only  on  the  exactness 
of  the  measuring  instruments  employed.  Speaking  absolutely,  this  condition 
of  equilibrium  is  never  attained,  and  we  may  say  the  deformation  increases 
indefinitely.  It  approaches,  however,  a  limiting  value  (as  an  asymptote), 
especially  in  the  case  of  elastic  deformations,  and  even  for  permanent  defor- 
mations the  time  may  be  found  beyond  which  the  remaining  deformation 
will  not  exceed  a  given  amount." 

It  is  admitted,  however,  that  for  metals  at  ordinary  temperatures  a  ten- 
sion test  (for  instance),  extended  over  a  few  minutes'  time,  gives  practically 
the  same  results,  in  every  respect,  that  would  be  obtained  by  any  slower 
imposition  of  the  load.  This  has  been  thoroughly  established  by  Bauschin- 
ger,  as  well  as  by  Considere  and  Le  Chatelier.  Zinc  and  tin  are  exceptions 
to  this  law,  comparatively  small  external  forces  causing  final  rupture  if  these 
forces  continue  active.  Copper  and  aluminum  also  fail  under  a  somewhat 
smaller  permanent  load  than  is  required  to  produce  rupture  in  ordinary 
tests.*  It  is  well  known  that  timber  yields  continually  under  about  one  half 

*  Report  of  the  French  Commission,  vol.  i.  p.  93. 


306  THE  MATERIALS  OF  CONSTRUCTION. 

the  breaking-load,  and  this  half -load,  permanently  placed,  may  ultimately 
cause  failure.  For  all  kinds  of  test  specimens  of  wrought  iron  and  steel,  and 
other  structural  metals,  at  ordinary  temperatures,  a  test  extending  to  one 
minute  or  more  may  be  considered  as  giving  normal  results. 

For  very  rapid  tests,  or  where  rapture  occurs  in  less  than  a  minute,  the 
breaking-load  increases  and  so  does  the  ultimate  elongation.  In  the  case  of 
soft  steel,  however,  which  has  a  great  local  reduction  of  area,  the  elongation 
diminishes  as  the  test  period  decreases,  reaching  a  minimum  for  a  period  of 
about  one  minute,  and  then  the  elongation  rapidly  increases  again  for  very 
quick  tests,  because  it  then  reduces  in  cross-section  more  uniformly  through- 
out its  entire  length. 

It  has  been  shown  by  M.  Considere  *  that  the.  stress-diagram  giving  the 
simultaneous  relation  between  stress  and  deformation  is  very  different  under 
very  quick  impositions  of  load,  as  in  case  of  a  shock,  or  impact,  from  the 
diagram  for  ordinary  laboratory  static  tests  of  more  than  one  minute  dura- 
tion. His  results  are  shown  in  Fig.  52,  p.  79.  This  subject  is  fully  dis- 
cussed in  Art.  292,  where  impact  tests  are  described. 

In  conclusion  it  may  be  said  that  in  all  ordinary  tests  of  metals  the  test 
period  should  fall  between  one  and  six  minutes. 

261.  Significant  Limits  of  Deformation. — Ever  since  the  properties  of 
building  materials  have  been  studied,  "  the  elastic  limit  "  has  been  defined 
both  as  the  greatest  load  which  will  not  produce  a  permanent  set,  and  as  the 
greatest  load  at  which  deformation  remains  proportional  to  the  load,  or 
stress.  It  has  commonly  been  supposed  that  these  two  limits  were  one  and 
the  same,  and  in  the  commercial  testing,  which  has  probably  been  carried  on 
in  America  to  as  great  an  extent  as  in  any  country,  this  so-called  "  elastic 
limit"  has  been  observed  as  the  point  at  which  the  deformation  increases 
rapdly  under  a  constant  load,  or,  as  it  has  been  called,  the  "  yield-point." 
The  French  Commission  has  studied  this  subject  with  care,  and  after  mature 
deliberation  a  majority  have  agreed  to  adopt  three  critical  points,  as  follows: 

1.  The  elastic  limit  ("  la  limite  (Telasticite"\  or  the  unit  stress  beyond 
which  a  portion  of  the  deformation  remains  as  a  permanent  set.     (Point  E 
of  the  stress-diagram.) 

2.  The  proportional  elastic  limit  (la  limite  d'elasticite  proportioned,  or 
limite  des  deformations  proportionelles),  corresponding  to  the  point  where  the 
deformation  ceases  to  be  proportional  to  the  loads.     (Point  P  of  the  stress- 
diagram.) 

3.  'I  he  apparent  elastic  limit  (la  limite  d'elasticite  apparente,  or  origine 
des  deformations  sous  charge  constante),  corresponding  to  the  point  where  the 
deformations  increase  rapidly  without  any  increase  in  the  force  exerted. 
(Point  F  of  the  stress- diagram.) 

While  in  a  scientific  study  of  metals  it  may  be  important  to  determine  all 
these  three  limits  whenever  they  occur,  in  practical  or  commercial  testing 

*  French  Commission  Report,  vol.  n.  p.  344. 


MECHANICAL   TESTS  IN  GENERAL. 


307 


it  will  be  found  sufficient  to  observe  the  third  one  only,  or  the  second  only 
in  case  the  third  limit  does  not  obtain  for  that  material.  The  first  of  these 
limits  has  seldom  been  determined,  since  it  involves  a  release  of  the  stress 
by  removing  the  load.  This  involves  a  great  loss  of  time,  since  to  determine 
this  limit  accurately  the  load  would  have  to  be  released  for  each  small  incre- 
ment of,  let  us  say,  1000  pounds  per  square  inch  for  iron  and  steel.  The 
second  and  third  limits  can  be  determined  after  the  test  has  been  completed, 
provided  simultaneous  readings  of  the  load  and  deformation  were  taken 
during  the  test  at  frequent  intervals,  or  provided  an  autographic  stress- 
diagram  was  made  by  suitable  attachments  to  the  machine  and  test  specimen. 
The  third  limit  is  commonly,  but  not  accurately,  determined  in  commercial 
testing  in  America,  by  "  the  drop  of  the  weighing-beam,"  this  marking  the 
point  where  the  deformation  increases  for  very  ductile  metals  under  a  con- 
stant load. 

With  unrolled  (or  unforged)  castings  of  the  various  metals  any  load  pro- 
duces some  appreciable  permanent  set,  so  that  the  first  elastic  limit  does  not 
exist  for  such  materials.  It  is  probable  that  this  is  also  true  to  an  inappre- 


FIG.  247.— Average  Curve  of  Four  Tests  of  |-in.  Wrought-iron  Rods. 

Rep.,  1888.) 


(Wat.  ATS. 


ciable  degree  of  all  the  rolled  metals,  so  that  this  is  a  very  unreliable  and 
unsatisfactory  test  of  any  important  property  of  materials.  The  law  of 
proportionality  is  much  better  defined,  but,  owing  to  the  mixed  character  of 
the  elementary  forms  entering  into  the  composition  of  all  metal  products, 
even  the  purest,  this  law  is  often  found  to  fail  when  the  most  refined  means 
of  measurement  are  employed,  since  there  then  seems  to  be  no  strictly  con- 
stant ratio  between  the  load-increments  and  the  corresponding  increments 
of  the  deformation,  and  hence  the  exact  point  where  this  ratio  begins  to 


308 


THE  MATERIALS  OF  CONSTRUCTION. 


change  is  in  these  cases  difficult  to  fix.  In  such  cases,  by  plotting  the 
deformation  to  a  very  large  scale  with  the  loads,  one  can  determine  graphi- 
cally, as  in  Fig.  2-47,  about  where  the  deformation  increments  begin  to 
increase.  The  second  and  third  elastic  limits  are  marked  on  this  diagram 
"  true  elastic  limit  "  and  "  yield-point  "  respectively.  ^The  "  apparent 
elastic  limit,"  or  "  yield-point,"  is  the  most  important  and  significant  of  the 
three,  as  well  as  the  most  easily  determined,  but  in  high  carbon-steel, 
especially  in  hard-steel  wire  and  in  all  cast  metals,  and  often  in  wrought 
iron,  this  point  does  not  appear,  in  which  case  the  "  proportional  elastic 
limit"  takes  its  place,  as  shown  in  Fig.  249,  where  it  is  marked  as  the 


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FIG.  248.— Typical  Stress-diagram  of  Hard-drawn  Brass.     ( Wat.  Ars.  Rep.,  1886.)    (The 
"  U.  S.  Elastic  Limit "  is  that  given  in  the  published  report.) 


"  true  elastic  limit."  Sometimes,  also,  when  point  ^is  very  marked,  point 
P  is  found  above  it,  as  in  Figs.  7  and  8,  pp.  15  and  16. 

262.  All  these  Absolute  Elastic  Limits  Unsatisfactory. — It  is  proposed 
now  to  show  that  no  one  of  the  three  definitions  of  elastic  limit  given  in 
Art.  261  can  be  used  in  practice.  They  all  will  be  shown  to  be  either  abso- 
lutely indeterminate  or  wholly  dependent  on  the  delicacy  of  the  measuring 
apparatus,  rather  than  on  the  qualities  of  the  material  tested. 

Thus  the  first  two  definitions  undertake  to  fix  a  limit,  and  evidently  the 
position  of  this  limit  is  simply  the  point  where  either  the  permanent  set  or 
the  deviation  from  a  linear  relation  between  load  and  deformation  becomes 
measurable.  If  one  can  measure  accurately  to  0.0001  inch,  he  will  discover 
these  limits  earlier,  or  at  a  lower  stress,  than  if  he  can  only  measure  to  0.001 
inch.  The  French  Commission  recommend  that  measurements  be  made  to 


MECHANICAL   TESTS  IN  GENERAL. 


309 


the  nearest  0.001  mm.  or  to  ^-^or  inch.  To  discover  a  permanent  set, 
furthermore,  requires  a  constant  release  of  the  load,  which  is  liable  to  disturb 
the  deformation-measuring  apparatus,  and  in  any  case  the  load  at  which  a 
permanent  set  occurs  can  only  be  said  to  lie  between  two  particular  loads, 
the  greater  of  which  has  produced  the  first  permanent  set  observed.  The 
time  and  trouble  involved  in  releasing  the  load  so  often  will  act  to  remove 
this  test  from  nearly  all  scientific  and  commercial  work. 

It  has  generally  been  assumed  that  the  first  two  definitions  of  elastic 
limit  given  in  Art.  261  locate  identical  points  in  the  stress-diagram,  but 


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FIG.  249. — Tension  Tests  of  Steel  Piano- wire.      Gauged  length  6  in.,  Diam.  0.04  in. 

(Wat.  ATS.  Rep.,  1894.) 

with  the  most  delicate  measuring  appliances  it  is  found  that  these  two  defi- 
nitions may  locate  points  very  far  apart. 

The  third  definition  is  also  indefinite,  since  it  remains  a  question  as  to 
which  load  is  to  be  taken,  the  higher  load  at  which  the  first  great  permanent 
elongation  occurred,  or  the  lower  load  under  which  this  elongation  continues 
to  spread  throughout  the  entire  length  of  the  bar.  These  often  differ  as 
much  as  from  3000  to  GOOO  pounds  per  square  inch.  (See  Figs.  7  and  8.) 

Again,  when  the  most  delicate  apparatus  is  employed,  several  specimens 
from  the  same  bar  of  the  most  uniform  material  may  give  elastic  limits  of 
either  of  the  first  two  kinds  which  differ  widely  from  each  other  and  hence 
become  mutually  contradictory.  In  other  words,  such  delicate  tests  are  quite 
worthless  for  all  practical  purposes,  i.e.,  the  results  are  not  characteristic.- 

263.  The  Apparent  Elastic  Limit.— The  term  "  relative  elastic  limit  " 
was  coined  by  the  author  in  1891,  to  be  used  in  his  work  of  testing  timber 
for  the  Forestry  Division  of  the  U.  S.  Agricultural  Department.  He  then 


310  THE  MATERIALS  OF  CONSTRUCTION. 

defined  it  as  the  point  on  the  stress-diagram  (of  tests  in  cross-bending) 
where  the  rate  of  deformation  is  fifty  per  cent  greater  than  it  is  at  the  origin 
(see  Figs.  247,  248,  and  249).  To  find  it  draw  a  tangent  to  the  stress-diagram 
at  the  origin,  and  then  lay  a  parallel  ruler  on  a  line  making  with  the  load 
line  an  angle  whose  tangent  is  fifty  per  cent  greater  than  that  of  the  original 
tangent  line,  and  then  move  the  ruler  until  its  edge  becomes  tangent  to  the 
stress-diagram,  and  draw  such  tangent  line.  The  "  relative  elastic  limit" 
is  then  located  by  eye  as  this  point  of  tangency.  In  the  tests  of  wooden 
beams  this  point  usually  falls  on  the  diagram  where  its  curvature  is  about 
the  most  rapid  (radius  of  curvature  a  minimum),  and  in  all  tension  stress- 
diagrams  of  the  various  metals  it  will  be  found  to  mark  a  well-defined  point, 
whose  coordinates  are  practically  fixed  and  constant  for  the  same  material. 
While  this  point  is  certainly  beyond  all  "  true  elastic  limits  "  when  defined 
as  limits,  yet  in  the  metals  it  will  be  found  to  fall  very  little  beyond  such  true 
limits.  In  fact  it  commonly  falls  below  the  "  elastic  limit  "  recorded  in  all 
the  Watertown  Arsenal  Tests,  where  the  deformations  were  measured  and 
recorded  to  the  nearest  To~Vr?r  °^  an  incn>  as  shown  in  Figs.  9  and  248, 
and  many  others  in  Chapter  XXIV. 

The  French  Commission  make  use  of  the  term  "apparent  elastic  limit  " 
to  indicate  what  in  England  is  called  the  "  yield-point  "  or  "  break-down 
point,"  and  in  Germany  is  called  the  "  beginning  of  great  elongations." 
But  with  such  materials  as  cast  iron,  high  carbon-steel,  and  often  with 
wrought  iron  and  other  metals  there  is  no  "  yield-point,"  or  no  point  where 
the  material  deforms  under  a  constant  load,  unless  it  be  at  the  point  of 
maximum  load,  to  which  of  course  it  is  not  intended  to  apply.  The  term 
"  apparent  elastic  limit  "  in  this  sense,  therefore,  has  not  a  universal  appli- 
cation, and  hence  cannot  be  used  as  the  commercial  elastic  limit  to  be  em- 
ployed in  practical  tests. 

The  term  "  apparent  elastic  limit  "  has  not  as  yet  come  into  use  in 
English;  and  if  it  now  be  defined  arbitrarily  as  the  term  "  relative  elastic 
limit "  is  defined  above,  it  could  have  this  specific  meaning  and  would  be  of 
universal  application. 

When  so  located  it  will  be  found  at  practically  the  same  point  on  all  tests 
of  like  kind  on  similar  materials.  It  is  therefore  characteristic  of  the 
material. 

It  does  not  require  the  use  of  expensive  and  troublesome  appliances  for 
its  accurate  location.  Relatively  crude  appliances  can  be  used  to  measure 
the  deformations ;  and  though  these  may  not  fall  on  a  smooth  curve,  a  mean 
line  drawn  through  them,  as  the  stress-diagram,  furnishes  a  satisfactory 
means  of  locating  this  "  apparent  elastic  limit. "  It  is  therefore  a  practically 
determinate  function. 

It  can  readily  be  determined  from  an  automatically  registered  stress- 
diagram,  of  any  description,  thus  admitting  of  a  continuous  and  uninter- 
rupted progress  of  loading,  so  that  the  conditions  of  a  test  can  be  exactly 
duplicated  as  to  speed,  which  cannot  be  done  when  the  test  is  stopped  to 


MECHANICAL   TESTS  IN  GENERAL.  311 

take  deformation  readings.  It  is  therefore  a  true  relative  limit  of  the  elastic 
field. 

Although  this  point  is  slightly  beyond  the  true  elastic  limit,  it  will  mark 
a  point  corresponding  to  a  permanent  set  much  less  than  can  be  measured  on 
any  scale  by  the  naked  eye,*  and  hence  it  may  be  regarded  as  the  true  elastic 
limit  for  commercial  purposes. 

It  serves  perfectly  to  classify  materials  as  to  the  maxim  am  loads  they  can 
resist  without  receiving  deformation  which  would  injure  them  for  continued 
service,  these  being  the  real  "  ultimate  loads"  for  all  practical  purposes. 
It  marks,  therefore,  the  most  valuable  and  important  property  of  all  engineer- 
ing or  building  material.  In  other  words,  it  is  the  most  essential  character- 
istic point  on  the  stress-diagram. 

In  the  opinion  of  the  author  of  this  work,  therefore,  an  "  apparent  elastic 
limit,"  defined  and  determined  as  here  described,  is  the  best  if  not  the  only 
satisfactory  solution  of  this  troublesome  question.  The  fifty  per  cent  increase 
in  the  rate  of  deformation  was  chosen  as  being  about  the  least  which  would 
mark  a  well-defined  point  of  tangency  on  the  stress-diagram.  Since  it 
always  marks  a  point  which  corresponds  to  an  extremely  small  permanent 
set,  there  would  seem  to  be  no  objection  to  its  use. 


*  Seldom  more  than  one  one-thousandth  of  one  per  cent  of  the  measured  length.  It 
is  a  maximum  in  the  case  of  the  high-grade,  hardened  steel  wire,  shown  in  Fig.  249, 
where  it  reaches  about  ^  of  one  per  cent. 


CHAPTER   XV. 
TENSION  TESTS. 

264.  Significance  of  Tension  Tests. — Tension  tests  are  at  once  more  com- 
mon, more  readily  made,  and  more  useful  in  revealing  the  true  character  of 
a  metal  than  any  other  kind  of  mechanical  test.  In  fact,  when  other  kinds 
of  tests  are  made  it  would  commonly  be  well  to  accompany  them  with  a  few 
tensile  tests  for  the  purpose  of  being  able  better  to  coordinate  the  results 
with  those  obtained  on  other  materials  by  similar  tests,  or  on  like  materials 
by  different  tests.  In  this  connection,  however,  it  is  well  to  remember  that 
all  the  metals  are  wanting  in  strict  homogeneity,  and  that  they  may  be 
regarded  as  aggregations  of  more  or  less  dissimilar  elements  embedded  in  a 
common  matrix,  somewhat  like  granite.  (See  Arts.  105  and  108.)  For 
instance,  the  planes  of  rupture  will  be  different  for  different  kinds  of  tests 
on  the  same  specimen,  and  hence  the  strength  developed  will  be  that  of  a 
different  combination  of  elements  in  each  case.  Also,  the  strength  to  resist 
various  kinds  of  stress  may  lie  4n  entirely  different  elements  of  the  aggrega- 
tion, as,  for  instance,  in  the  case  of  cast  iron  the  strength  to  resist  tension  is 
the  strength  of  the  graphitic  carbon  matrix  in  which  the  iron  crystals  are 
embedded,  while  the  strength  in  compression  is  largely  the  strength  of  the 
iron  crystals  themselves.* 

What  we  call  the  maximum  strength  of  the  material,  therefore,  or  its 
strength  at  rupture,  is  not  usually  the  sum  of  the  maximum  resistances  of  the 
several  elementary  portions  of  the  cross-section,  since  they  do  not  all  distort 
equally.  It  is  often  the  case  that  actual  rupture  occurs  successively  over 
many  elementary  portions  of  the  broken  section  before  the  final  failure 
occurs.  More  especially  is  this  true  of  the  elastic  limits  of  the  material, 
while  with  iron  and  steel  castings  this  failure  in  detail  is  so  prominent  as  to 
cause  the  stress-diagram  to  be  a  curve  almost  from  the  beginning  of  the  load- 
ing. Here,  too,  the  irregular  shrinkage  often  leaves  very  great  internal 
stresses  in  the  body,  which  causes  some  portions  to  come  to  their  elastic 
limits  and  ultimate  strength  much  earlier  than  others,  again  giving  rise  to  a 
curved  stress-diagram. 

For  these  reasons  we  find,  when  the  most  delicate  means  are  employed  to 
measure  deformations  under  increasing  loads,  that  in  almost  no  case  is  the 

*  M.  Osmond. 

312 


TENSION  TESTS.  313 

deformation  strictly  proportional  to  the  load,  and  that  even  very  small  loads 
will  produce  some  little  permanent  deformation  or  set.  This  is  why  the 
definitions  given  in  Art.  261  must  depend  on  certain  arbitrary  limits  of 
deformation  and  set,  and  are  not  true  absolutely  as  they  have  hitherto 
commonly  been  defined. 

The  tension  test  is  especially  well  calculated  to  show  what  local  irregulari- 
ties may  be  found  in  a  finished  product,  and  to  indicate  to  what  extent  the 
work  of  forging  (rolling  or  hammering)  has  produced  that  degree  of  homo- 
genity  expected  of  it. 

The  tension  test  is  more  readily  standardized  than  any  other  so  as  to  be 
independent  of  "  personal  equation  "  and  of  variations  in  the  testing-machines 
employed.  It  also  demands  the  least  amount  of  preparation  of  the  test 
specimen,  if  tests  are  to  be  made  only  for  commercial  purposes.  Except  for 
the  inherent  want  of  uniformity  or  of  homogeneity  mentioned  above,  there- 
fore, the  tension  test  may  be  made  to  give  typical  and  uniform  results,  and  it 
should  be  considered  as  the  best  single  test  to  make  on  any  of  the  metals. 

265.  Selection  of  the  Test  Specimens. — Test   specimens  may  be  taken 
either  from  the  finished  product  or  from  the  material  when  poured  if  it  is 
derived  from  a  fluid  condition.     In  American  steel  mills  it  is  common  to 
roll  (or   hammer)  a  test  rod  from  a  small   ingot  poured  from  each  heat, 
whether  it  be  of  the  Bessemer  or  the  open-hearth  process,  and  the  maker 
depends  on  the  tests  made  on  this  bar  to  guide  him  in  the  further  use  of  the 
ingots  poured  from  that  heat.     The  user  also  is  often  satisfied  with  these 
tests,  especially  when  his  requirements  are  not  very  rigid. 

In  making  iron  and  steel  castings  it  is  common  to  have  test  samples 
cast  in  the  same  moulds  with  important  castings,  and  joined  thereto,  so  that 
they  shall  represent,  of  necessity,  the  identical  metal  of  which  the  structural 
form  is  composed.  If  special  moulds  are  used  for  these  test  specimens,  they 
should  be  of  dry  sand,  under  a  head  of  at  least  eight  inches,  and  with  an 
inclination  of  at  least  one  in  five  to  allow  the  escape  of  the  gases.  With 
very  heavy  castings  (over  three  inches  in  thickness)  test  specimens  may  be 
cut  from  the  head  itself  which  is  cut  off  from  the  upper  end  of  the  casting. 

If  the  specimens  are  taken  from  rolled  structural  forms,  they  should  be 
taken  from  the  thicker  parts,  which  have  received  the  least  work  in  the 
rolls.  The  thinner  parts  are  always  harder,  have  higher  elastic  limits  and 
greater  ultimate  strength. 

With  wrought  iron  a  great  difference  will  be  found  in  specimens  cut  with 
and  across  the  direction  of  the  rolling,  the  former  having  much  higher 
strength  and  a  greater  ductility.  In  steel  plates  there  is  little  difference, 
and  in  rolled  brass  and  copper  plates  there  is  no  difference.  In  the  case  of 
the  bronzes  it  is  necessary  to  have  test  samples  poured  from  different  parts  of 
the  same  melting,  as  the  mixture  changes  its  characteristics  rapidly  when  in 
a  melted  state. 

266.  The  Preparation  of  the  Test  Specimen. — In  order  that  the  test 
specimen  may  fairly  represent  the  material  under  examination,  or  the  par- 


314  .THE  MATERIALS  OF  CONSTRUCTION. 

ticular  plate,  or  bar,  or  rolled  form  from  which  it  is  to  be  taken,  it  is  neces- 
sary to  observe  a  number  of  rigid  requirements. 

The  specimen  must  be  obtained  by  cutting  it  out  in  a  way  that  will  leave 
it  perfectly  straight.  If  it  is  bent  in  getting  it  out,  it  should  be  heated  to 
straighten  it;  but  this  may  often  change  the  original  molecular  arrangement, 
and  should  be  avoided  if  possible.  When  the  specimen  is  cut  from  a  larger 
portion  of  a  plate  or  rolled  form  by  shearing,  it  will  invariably  take  a  curved 
form.  In  this  case  the  plate,  or  form,  should  be  sheared  aivay  from  the 
specimen,  in  narrow  slices,  so  as  to  leave  the  test  specimen  unbent.  If  the 
specimen  is  bent  and  then  straightened,  it  raises  the  elastic  limit  and  hardens 
the  metal,  the  same  as  any  other  kind  of  cold  working.  Instead  of  shearing, 
some  milder  process,  such  as  planing  or  drilling  or  sawing,  should  be  resorted 
to  to  obtain  the  test  specimen.  For,  besides  the  bending  action  on  the  bar 
as  a  whole,  the  effect  of  the  shearing  or  punching  is  to  seriously  injure  the 
metal  for  about  an  eighth  of  an  inch  beyond  the  sheared  surface,  leaving  it 
so  non-ductile,  or  brittle,  that  it  will  not  elongate  appreciably,  and  hence 
under  a  tensile  test  these  surfaces  will  be  severed  very  early  in  the  test,  and 
the  cracks  so  started  may  cause  the  remainder  of  the  cross-section  to  tear 
asunder  in  detail.  To  prevent  this  action  on  sheared  or  punched  specimens, 
at  least  an  eighth  of  an  inch  of  thickness  should  be  removed  from  all 
punched  or  sheared  faces,  by  reaming,  planing,  or  filing.  The  effect  of  not 
doing  this  is  shown  in  various  figures  in  Chapter  XXVI,  where  both  punched 
and  drilled  test  specimens  of  one-fourth  inch  iron  and  steel  plates  had  been 
grooved  for  testing,  leaving  varying  widths  of  metal  between  the  bottoms 
of  the  grooves.  The  effect  of  this  variation  in  width  is  also  here  shown. 
Various  bending  tests  there  shown  also  exhibit  the  weakness  resulting  from 
shearing  and  punching. 

The  ordinary  lathe,  planer,  and  milling-machine  tools  are  not  suitable 
for  i\iQ  final  finishing  of  the  specimen,  as  they  tear  and  bruise  the  remaining 
metal,  giving  rise  to  a  condition  favorable  to  the  starting  of  incipient 
fractures  at  the  surface  of  the  specimen.  These  tools  may  be  used  for 
roughing  out  the  shape  desired,  but  it  should  be  finished  with  the  file,  and 
in  case  of  the  softer  metals,  like  copper,  the  file  should  be  followed  with  fine 
emery-paper. 

Castings  should  be  cut  down  about  an  eighth  or  a  tenth  of  an  inch  from 
the  rough  exterior,  on  the  reduced  section,  and  they  should  also  be  trued-up 
on  the  ends  which  are  to  be  gripped.*  Rectangular  edges  should  always  be 
taken  off  by  a  file  to  remove  any  incipient  cracks  or  irregularities  which  may 
be  left  here  by  a  kind  of  crushing-down  action  of  the  tools  operating  on  one 
or  both  of  the  plane  faces  meeting  on  these  lines.  Test  specimens  of  the 
softer  metals  should  never  be  beaten  with  a  steel  hammer,  but  with  wooden 
or  copper  mallets,  if  it  is  necessary  to  use  such  means  to  straighten  them. 

Standard  shapes  of  test  specimens  are  shown  in  Fig.  251. 

*  For  commercial  purposes  a  cheap  form  of  specimen  which  is  tested  without  turn- 
ing down  at  all  is  shown  in  Chapter  XXIV. 


TENSION  TESTS. 


315 


KULES    OF    THE    FRENCH    COMMISSION    FOR    TENSION    TESTS. 

1.  The  test  should  be  continuously  progressive. 

2.  The  duration  of  the  test  should  in  a  general  way  increase  with  the  volume 
of  the  specimen. 

3.  For  standard  tests  on  specimens  of  ordinary  dimensions  of  which  the  sectional 
area  is  not  more  than  one  square  inch  (600  sq.  mm.)  and  the  measured  length  not 
more  than  eight  inches  (20  cm.)  it  seems  that  the  duration  of  the  test  should  be 
included  between  one  and  six  minutes. 

4.  For  test  specimens  having  a  thickness  less  than  0.2  in.  (5  mm.)  the  duration 
of  the  test  should  be  less  than  thirty  seconds. 

5.  It  is  necessary  to  avoid,   especially  with  soft  metals,   producing  a  sensible 
heating  of  the  test  bars. 

267.   Standard  Dimensions  of  Tension-test  Specimens.  —  It  has  been 
shown  *  that  so  long  as  the  test  specimens  of  a  given  material  maintain  the 


FIG.  250. — Showing  the  Constancy  of  the  Strength  and  of  the  Elongation  when 
— =  =  a  constant  (8  in  this  case).  Each  result  is  the  mean  of  five  tests  on  the  same 
material.  (French  Com.  Rep.,  1894,  vol.  in.  p.  72.) 


*  By  MM.   Lebasteur,   Marie,    and   Barba. 
23. 


See  Rep.  French  Commission,  vol.  in. 


316  THE  MATERIALS  OF  CONSTRUCTION. 

same  relative  dimensions,  or  are  geometrically  similar  in  form,  the  strength 
and  the  percentage  of  elongation  remain  constant,  as  shown  in  Fig.  250. 
The  French  Commission  have,  therefore,  adopted  the  relation  f  =  6G.67^4, 
or  for  cylindrical  specimens  I  —  7.2d,  where  I  is  the  measured  length  on 
which  percentage  of  elongation  is  computed.  An  eight-inch  specimen  would 
then  be  1.11  inch  in  diameter,  or  nearly  1  sq.  in.  in  area  of  cross-section. 
Since  this  relation  between  I  and  A  was  chosen  for  convenience  (for  I  =  200 
mm.,  A  =  600  sq.  mm.),  persons  using  inch  units  might  well  choose  the 
relation  I  =  8^7,  or 

F  =  8IA (1) 

For  square  sections,  therefore, 

I  -  96, (2) 

while  for  round  sections 

(3) 


these  being  intermediate  between  the  French  and  the  German  standard 
dimensions.* 

Equations  (1),  (2),  and  (3),  therefore,  may  be  employed  in  finding  what 
length  of  specimen  to  use  to  give  comparable  and  consistent  percentages  of 
elongation,  when  the  excessive  elongation  near  the  broken  section  is  included. 

If  it  is  practicable  to  so  prepare  the  specimen  as  to  make  the  area  of  the 
cross-section  nearly  constant,  then  a  fixed  length  of  specimen  could  be  used 
for  all  tests.  Thus  for  the  standard  length  of  eight  inches  the  diameter  of 
round  specimens  would  be  one  inch.  Where  the  cross-section  varies  from 
this  the  lengths  should  vary  in  accordance  with  equation  (3).  Thus 

For  diameters  of  £  inch  make  I  =  7  inches. 


"  f     " 

"     Z=  6 

"  £    " 

"     1  =  5 

•"*  " 

"     7  =  4 

<  t     3          a 

8 

«     Z  =  3 

u   i       u 

'tf     ?  =  2 

For  plate  tests  we  have,  from  (2), 

F  =  SIA  =  Slbt,     or     I  =  9  VU (4) 

Since  it  is  common  to  prepare  several  of  these  together  in  a  milling- 
machine,  it  is  desirable  to  have  a  common  width  for  these  tests,  and  a  width 
of  one  inch  has  been  usually  employed  in  America.  This  may  be  done  if 
the  lengths  are  varied  to  give  comparable  results.  Thus,  from  eq.  (4), 
I  =  9  Vbt,  the  following  scheme  of  lengths  and  thicknesses  is  derived,  the 
width  being  one  inch  in  all  cases: 

*  The  German  Commissions  have  agreed  on  I  =  11.3  V'A=-  IQd  for  round  section 
and  11.36  for  square  sections. 


TENSION  TESTS.  317 

For  plates  £  inch  thick  make  I  =  4^  inches. 


"         "  f  "  "  "  I  —  5i 

u  I  «  if  «  I-  61 

ff  fi  5  ff  if  a  7  __  r~ 

fi  if  3  fi  if  ii  7   __  /J'S 


r 


if  if  7  if  if  if  7     _      Q  J_  .  .' 

For  thin  sheet  metal  make  the  measured  length  always  four  inches,  and 
use  three  standard  widths  as  follows  : 

For  thicknesses  from  0.1  inch  to  0.2  inch  make  width  =  £  inch. 

"      0.05   "•   "  0.1     "        "         "      =  f     " 
less  than  0.05  inch  "         li      =  £     « 

All  these  relative  dimensions  agree  closely  with  those  recommended  by 
the  French  Commission  (1895). 

The  measured  portion  of  the  reduced  section  (called  I  in  the  above 
discussion)  must  be  removed  from  the  shoulders  by  a  distance  at  least  as 


1 

.                               L                                                                                                                                                       jt 

,  ^  j  ,  M 

f       1. 

d                                               ct> 

FIG.  251.— Standard  Dimensions  for  Rectangular  and  Cylindrical  Test  Specimens. 

great  as  the  diameter  or  thickness  of  the  test  bar,  in  order  to  avoid  the  effect 
of  these  enlarged  portions  in  reducing  the  elongation.  The*  reduction  of  the 
percentage  of  elongation  near  the  ends  is  well  shown  in  Fig.  252,  where  the 
bar  had  a  total  reduced  length  of  15  inches  and  a  diameter  of  1^  inches. 
Steel  bars  of  this  shape  will  break  near  the  centre,  while  wrought-iron  bars 
will  break  at  various  distances  from  the  centre,  with  a  more  uniform  distri- 
bution of  the  elongation. 

268.  Tetmajer's  Analysis  of  the  Elongation  of  Tension-test  Specimens.*— 

The  typical  forms  of  tension-test  specimens  are  shown  in  Fig.  251,  where  both  round 
and  rectangular  sections  are  given.  It  has  been  shown  by  numerous  experiments 
that  the  strength  and  the  reduction  of  area  are  somewhat  dependent  on  the  form  of 
the  test  specimen,  while  the  elongation  is  very  greatly  dependent  on  these  relative 
dimensions.  This  is  well  illustrated  in  the  reproduced  photographs  shown  in 
Fig.  10,  and  also  in  the  elongation-diagrams  Figs.  252  and  253.  Here  are  shown  first 
the  original  specimens,  then  the  specimen  stretched  to  its  maximum  loading,  the 
elongation  being  nearly  uniformly  distributed  over  the  length,  and  finally  the  speci- 
men greatly  reduced  at  one  point  where  rupture  is  about  to  occur.  It  is  evident, 

*  Tetmajer's  Communications,  vol.  iv. 


318 


THE  MATERIALS  OF  CONSTRUCTION. 


PIG.  252.  —  Showing  Distribution  of  the  Elongation  over 
2  in.  in  Diameter.     (Rep.  Fr.  Com.,  vol. 


-i  -----  1 

a  Steel  Bar  15  iu.  Long  and 
in,  PI.  n.) 


FIG.  253.— Showing  the  Variation  in  the  Distribution  of  the  Elongation  of  the  Several 
Inch-spaces  of  Six-inch  Test  Bars  of  Steel  and  Wrought  Iron  0.56  in.  in  Diameter. 
(Wat.  Ars.  Rep.,  1890.) 


TENSION  TESTS. 


319 


from  a  study  of  these  specimens,  that  the  total  elongation  of  tension-test  specimen 
may  be  divided  into  two  distinct  parts,  namely: 

1.  The  general  elongation. 

2.  The  local  elongation. 

It  will  further  appear  that  the  local  elongation  is  nearly  the  same  in  all  cases, 
and  is  practically  independent  of  the  length,  while  the  general  elongation,  having 
occurred  uniformly  along  the  bar,  is  directly  proportional  to  the  length. 
If  I  =  measured  length  of  specimen, 
Al  —  total  elongation, 
A  =  proportional  distributed  elongation 
distributed  elongation 
~~T~          ~' 
Ah  =  total  local  elongation 

then  A  may  be  found  for  any  given  test  by  measuring  Al  for  two  lengths  of  the 
same  specimen,  each  to  include  the  broken  section.  Since  the  standard  length 
of  specimen  is  8  inches  (200  mm.),  it  usually  will  be  found  convenient  to  use  8 
inches  and  4  inches  for  these  two  lengths.  If  the  specimen  be  marked  originally 
every  inch,  then  after  it  has  broken  two  sets  of  these  marks  may  be  chosen,  each 
pair  to  include  the  fracture,  and  to  be  points  originally  8  inches  and  4  inches  apart 
respectively.  Then  we  may  have 

Ah  =  8A  +  A19 

Ah  =  4/1  +  Ah 


Ah  -  Ah  =  4A 
or 

A  —  \(Ah  —  Ah] (1) 

Til  is  function,  A,  obtained  in  this  way,  is  independent  of  the  length  of  the  speci- 
men, and  is  the  true  characteristic  elongation  of  the  material. 

It  would  seem  that  this  function  is  the  one  to  be  generally  adopted  as  the  true 

index  of  the  ductility  of  the  material.     Unfortunately  custom  has  established  -j  as 


0        20        40 

FIG.  254. — Elongation  of  a  Specimen  of  Copper  200  mm.  Long  for  the  Loads  as  given. 

(Fr.  Com.  Rep.,  vol.  in.  PI.  vn.) 

the  ductility  function,  or  "the  percentage  of  elongation,1' and  this  varies  greatly 
with  the  ratio  of  length  to  form  and  area  of  cross-section. 

Professor  Tetmajer  shows  that  the  following  relative  dimensions  give  practically 
equal  percentages  of  total  elongation : 

(A)    CYLINDRICAL    SPECIMENS. 


Diameters  .  .                                         ... 

0.4  in 

0.6  in. 

0.8  in. 

1.0  in. 

Observed  length  

4.0  in. 

6.  4  in. 

8.0  in. 

10.0  in. 

Mean  observed  elongation,  "  Phoenix"  steel.  .. 

30.1* 

30.  4# 

30.  5# 

30.  6# 

320  THE  MATERIALS  OF  CONSTRUCTION. 

(B)    RECTANGULAR    SPECIMENS,    ALL    0.4    IN.    THICK. 


Ratio  :  b-  = 

t 

1.0 

1.5 

2.0 

2.5 

3.0 

3.5 

4.0 

4.5 

5.0 

Observed  length,  iiiches.  . 

4.0 

4.8 

6.0 

7  2 

8.0 

8.0 

8.0 

8.4 

9.2 

Mean  observed  percentage 
of  elongation  

270 

27.2 

27  2 

26  8 

26.1 

25.7 

26.1 

26.7 

27.0 

Each  of  the  above  observed  elongations  in  Table  (A)  is  the  mean  of  five  tests  and 
in  Table  (B)  of  ten  tests,  and  the  results  indicate  that  equivalent  lengths  were  used. 
When  the  length  was  taken  as  8  inches  in  each  case,  the  percentage  of  elonga- 
tion in  Table  (A)  ranged  from  26.5  to  32.4,  while  in  Table  (B)  it  ranged  from  21.3 
to  28.6.  These  results  are  consistent  with  the  rules  laid  down  by  the  French  Com- 
mission and  which  the  author  has  interpreted  approximately  in  English  measures  in 
the  previous  article. 

269.  The  Time  Function  of  Tension  Tests  is  not  an  important  one. 
Bauschinger  has  shown  that  within  the  ranges  of  practicability  the  time 
element  is  of  no  consequence.  This  is  also  shown  in  Fig.  255,  where  results 

~\70 


PEf.D  /A 


CO 


40 


30 


/ 


234- 

FIG.  255.— Showing  the  Effect  of  Pulling  Speed  of  the  Testing-machine  on  the  Recorded 
Results  with  Structural  Steel.     (Campbell's  Structural  Steel,  p.  253.) 

obtained  with  the  greatest  rapidity  obtainable  in  the  American  standard 
testing-machines  are  compared  with  results  from  very  slow  tests,  with  very 
little  difference  in  the  results.  The  greatest  recorded  differences  are  found 
in  the  elastic  limit;  but  as  these  were  all  observed  by  the  "drop  of  the 
beam,"  it  is  likely  that  the  speed  had  more  to  do  with  the  obtaining  of  the 
reading  than  it  had  with  the  real  action  of  the  material  itself. 

270.  Tension-test  Machines. — There  are  three  general  types  of  universal 
(tension,  compression,  and  cross-bending)  testing-machines  on  the  American 
market,  viz.,  hydraulic  machines,  screw-gear  machines,  and  the  Emery 
machines.  The  hydraulic-power  machines  have,  however,  been  practically 
abandoned  in  favor  of  the  screw-gear  for  all  experimental  and  commercial 


TENSION  TESTS. 


321 


purposes,  while  for  high  scientific  accuracy  and  an  incredible  delicacy 
nothing  ever  made  can  compare  with  the  Emery  machines.*  The  first  two 
varieties  of  machine  owe  their  present  high  state  of  development  largely  to 
Mr.  Tinius  Olsen,  and  the  Emery  machine  was  originally  designed  by  Mr. 


A.  H.  Emery,  but  has  since  been  greatly  simplified  and  improved  by  Wm. 
Sellers  &  Co.,  the  present  manufacturers. 

The  hydraulic  machines  have  some  advantages  when  operated  by  hand, 
but  they  all  have  the  disadvantage  that  it  is  impossible  to  maintain  a  given 

*  The  hydraulic  and  screw-gear  machines  are  made  by  Tinius  Olsen  and  by  Riehle 
Bros.,  and  the  Emery  machines  by  "Win.  Sellers  &  Co.,  all  of  Philadelphia,  Pa. 


322  THE  MATERIALS  OF  CONSTRUCTION. 

load  without  continuous  pumping  to  supply  the  small  leakage  which  always 
occurs. 

The  Olsen  screw-gear  100,000-lb.  testing-machine,  shown  in  Fig.  256, 
will  be  taken  as  a  type  of  the  testing-machines  which  are  almost  exclusively 
employed  in  America.  The  power  is  applied  to  the  pulleys  26  and  27,  the 
former  used  for  direct  (downward)  and  the  latter  for  reverse  (upward) 
motion  of  the  moving  cross-head,  5.  Extremely  slow  speed  is  obtained  by 
throwing  into  contact  the  small  friction-gear  35,  operating  upon  the  large 
wheel  34,  which  is  rigidly  attached  to  the  driving-shaft.  This  is  effected  by 
drawing  on  the  chain  37  by  turning  the  hand-wheel  39,  which  tightens  the 
band  42  and  starts  35  to  revolving.  The  band-wheels  2G,  27,  and  43  all 
revolve  freely  on  the  driving-shaft,  except  as  2G  or  27  is  made  fast  to  it  by 
the  friction-clutch  28,  30,  through  the  hand-lever  33.' 

A  medium  speed  of  the  moving  cross-head  is  obtained  by  simply  throwing 
26  in  gear  by  the  hand-lever  33,  and  a  high  (upward  or  downward)  speed  is 
attained  by  changing  the  gears  by  means  of  lever  25,  the  upward  speed 
greatly  exceeding  the  downward  because  of  the  different  band  connections 
on  the  direct  and  on  the  reversing-pulleys  26  and  27  respectively. 

The  moving  cross-head,  5,  is  brought  down  by  the  turning  of  four  screws, 
one  at  each  corner,  only  two  of  which  are  visible  in  Fig.  256.  A  tension- 
test  specimen  is  placed  between  this  moving  head-piece  and  the  fixed  cross- 
head  above,  being  gripped  in  each  by  means  of  hardened  steel  wedges  with 
grooved  faces.  The  pull  on  the  specimen  is  thus  transmitted  through  the 
four  cast-iron  columns,  2,  to  the  weighing-table,  3,  which  rests  by  means  of 
fixed  spurs  upon  the  three  weighing-levers,  117.  Between  these  and  the 
weighing-beam,  118,  there  is  one  intermediate  multiplying-lever  (not  num- 
bered). The  large  poise,  106,  in  this  machine  is  supposed  to  be  moved  by 
means  of  the  screw  105,  which  is  under  automatic  electric  control.  When 
the  beam  lifts,  the  screw  is  put  in  motion;  and  when  it  leaves  its  upper  con- 
tact the  screw  stops  its  motion.  The  weighing-beam  is  thus  automatically 
maintained  in  constant  balance.  If  operated  by  hand,  the  large  poise,  106, 
is  set  forward  by  full  revolutions  of  the  screw  by  means  of  the  handle  shown, 
and  the  intermediate  loads  indicated  by  balancing  with  the  small  poise  shown 
at  the  right-hand  end  of  its  scale,  118'.  When  operated  automatically  this 
poise  is  not  used,  and  the  fractional  part  of  the  total  load  is  read  on  a  grad- 
uated disk  attached  to  the  screw  at  the  left-hand  end,  but  not  clearly  shown 
in  the  figure. 

Compression  tests  are  made  by  attaching  a  compression-block  to  the  lower 
side  of  the  moving  cross-head,  and  inserting  the  specimen  between.it  and  the 
weighing-table,  3. 

Cross-breaking  tests  are  made  by  placing  the  end  bearings  on  the  weigh- 
ing-table (or  on  an  I-beam  resting  on  this  table  if  the  specimen  is  long),  and 
attaching  a  knife-edge  bearing  to  the  lower  side  of  the  moving  cross-head. 

A  machine  in  nearly  all  respects  quite  similar  to  the  above  is  that  shown 
in  Fig.  257,  made  by  Riehle  Bros.  The  poise  here  is  moved  by  a  chain 


TENSION  TESTS. 


323 


passing  over  a  driving-pulley,  which  pulley  is  operated  either  by  hand  or  by 
power  under  electrical  control,  the  same  as  the  screw  in  the  Olsen  machine. 
Only  two  screws  are  here  used  for  moving  the  pulling  cross-head,  instead  of 
four  as  in  the  former  case.  Both  forms  of  machines  are  made  in  the  highest 
style  of  the  art,  both  being  the  survival  of  the  fittest  in  a  long  succession  of 
types  of  testing-machines.  They  are  by  far  the  most  useful  and  convenient 
testing-machines  made,*  and  are  not  likely  to  undergo  much  change  in  the 


FIG  2.37. 

future.  (They  are  now,  1896,  being  sold  in  Europe.)  The  speeds  at  which 
the  machine  shown  in  Fig.  257  may  be  driven  directly  are  as  follows:  TV  in. 
per  min. ;  £  in.  per  min. ;  f  in.  per  min. ;  1-j-  in.  per  min. ;  and  8  in.  per  min. 
For  tests  of  low  ultimate  strength,  speeds  of  •§  in.  per  min.  and  of  4  in.  per 
min.  can  also  be  used.  The  higher  speeds,  down  to  f  in.  per  min.,  can  also 
be  used  in  raising  the  moving  head.  By  changing  the  speed  of  the  main 
shaft  from  which  power  is  obtained  all  these  speeds  can  be  increased  or 
diminished  at  pleasure.  The  speeds  as  given  above  are  for  150  revolutions 
per  minute  of  the  driving-pulleys  on  the  testing-machine. 

In  Fig.  258  is  shown  a  small  screw-gear  power  machine,  made  by  Eiehle 

*  The  author  offers  no  apology  for  not  giving  descriptions  of  any  of  the  scores  of 
styles  of  machines  which  have  been  built  and  which  are  still  in  use — mostly  in  Europe. 
They  will  never  be  built,  bought,  or  used  in  this  country,  and  most  of  them  can  be 
found  illustrated  in  the  Report  of  the  French  Commission,  1895,  vols.  n.  and  in. 


324 


THE  MATERIALS  OF  CONSTRUCTION. 


Bros,  in  capacities  of  20,000  Ibs.,  30,000  Ibs.,  40,000  Ibs.,  50,000  Ibs.,  and 
60,000  Ibs.,  with  hand-power  attachments,  and  automatic  weighing  appli- 
.ances  if  desired.  With  the  20,000-lb.  machine  the  hand-power  does  very 
well,*  although  steam  or  electric  power  is  always  preferable.  Autographic 


FIG.  258. 

recording  attachments  (see  Art.  275)  are  attached  to  these  the  same  as  with 
the  larger  machines.  They  are  too  small,  however,  for  general  commercial 
purposes. 

271.  Gripping  Devices. — A  great  variety  of  grinning  devices  have  been 
employed,  such  as  eyes  and  pins,  shoulders  and  snlit  Beeves,  screws-treads 
and  nuts,  and  plain  bars  with  wedge-grips  This  last  *orm  has  now  replaced 
all  others  in  America  except  such  as  mav  still  be  employed  on  some  of  the 
older  machines.  For  round  specimens  notched  grins  are  used,  while  with 
square  or  flat  specimens  the  plain  wedges  are  employed.  The  Eiehle  plain 
grips  are  swelled  in  the  centre  so  as  to  grip  the  specimen  hardest  along  its 

*  These  small  machines  are  the  best  patterns  for  students'  use.  It  is  better  to  have 
several  of  these  than  one  larger  machine.  They  serve  almost  every  purpose  in  a  course 
of  study  on  the  strength  of  materials. 


TENSION  TESTS. 


325 


FIG.  259. 


326 


TEE  MATERIALS  OF  CONSTRUCTION. 


axis  of  symmetry.     The  Olsen  grips  are  swivelled  on  spherical  bearings  at 
the  back  to  enable  them  to  more  readily  adjust  themselves  to  the  specimen. 


FIG.  260. 


The  wedge-grips  can  be  nsed  with  plain  bars  and  plates,  without  any  reduc- 
tion of  section,  as  well  as  with  specimens  specially  prepared  by  turning  down 
or  by  a  milling-machine. 


TENSION  TESTS. 


327 


272.  Similar  Machines  for  Various  Special  Purposes. — In  Fig.  259  is 
shown  an  Olsen  machine  designed  for  testing  full-sized  structural  specimens, 
whether  tension  or  compression  members,  or  beams,  and  made  in  capacities 
of  200,000,  300,000,  and  400,000  Ibs.  These  machines  have  all  the  rates  of 
motion,  and  the  automatic  weighing  and  autographic  recording  appliances 
described  with  the  smaller  machines.  The  height  may  be  made  almost  any- 
thing which  may  be  desired. 

In  Fig.  260  is  shown  a  similar  machine  of  300,000  Ibs.  capacity,  in  which 
the  four  cast-iron  corner-posts  are  replaced  by  two  large  compression-screws. 

Fig.  261  illustrates  a  convenient  and  cheap  machine  for  testing  hoop-iron 


FIG.  261. 


and  round  bars,  in  tension  only,  of  20,000  Ibs.  capacity,  suitable  for  office 
use.* 

In  Fig.  262  is  shown  one  form  of  a  wire-testing  machine,  made  by  Olsen, 
in  capacities  of  10,000,  15,000,  and  20,000  Ibs.  It  is  also  adapted  for  test- 
ing band-iron  and  other  forms,  and  could  also  be  used  for  compression  and 
cross-breaking.  (See  also  other  wire-testing  machines  in  Chap.  XXXIII.) 

Fig.  263  shows  a  form  of  cloth-  and  paper- testing  machine, j  having  a 

*  Made  by  Riehle. 

f  Made  by  both  Olsen  and  Riehle. 


TEE  MATERIALS  OF  CONSTRUCTION. 


capacity  of  200  Ibs.  on  one  inch  in  width  of  material,  while  Fig.  264  shows 
another  form,  for  paper  only,  of  100  Ibs.  capacity.  The  stress  is  indicated 
on  the  face  of  the  dial. 

Tension-testing  machines  for  breaking  cement  briquettes  are  shown 
and  described  in  Art.  324. 

273.  The  Emery  Testing-machine. — This  is  without  doubt  by  far  the 
most  perfect  weighing-machine  ever  devised.  It  was  originally  invented 


FIG.  262. 


and  constructed  by  Mr.  A.  H.  Emery,  C.E.,  for  the  use  of  the  U.  S.  Test 
Board  in  1879,  and  this  first  machine,  having  a  capacity  of  800,000  Ibs. 
in  both  tension  and  compression,  is  still  in  daily  use  at  the  U.  S.  Arsenal 


TENSION  TESTS. 


329 


at  Watertown,  Mass. 


It  is  now  manufactured  in  various  sizes  by  Wm. 
Sellers  &  Co.  of  Philadelphia,  who  have  modi- 
fied and  improved  the  original  plans  in  many 
respects.  It  is  not  too  much  to  say  of  this  ma- 
chine that  it  operates  absolutely  without  fric- 
tional  resistance,  tests  with  equal  accuracy  large 
and  small  specimens,  is  easily  and  quickly 
operated,  and  is  practically  indestructible  by 
any  amount  of  legitimate  use.  The  marvellous 
character  of  this  machine  merits  a  careful  study 


FIG.  263. 


FIG.  264. 


by  all  students  in  engineering,  and  an  attempt,  is  here  made  to  adequately 
describe  it.* 

The  essential  principle  of  this  machine  consists  in  a  means  of  transmit- 
ting a  definite  percentage  of  the  force  applied  to  the  specimen  to  the  scale- 
beams,  and  there  weighing  it  accurately,  without  any  friction  whatever  in 
the  receiving,  transmitting,  or  weighing  parts.  Hence  any  very  small 
increment  of  the  force  applied  is  weighed  with  equal  accuracy,  whether  this 
increment  is  added  to  a  great  or  to  a  small  previous  load.f  This  is  accom- 

*  The  author  has  been  greatly  aided  in  this  by  drawings  and  descriptions  made  by 
Mr.  Carl  G.  Barth,  M.E.,  who  is  one  of  the  joint  inventors  and  patentees  of  the  various 
improvements  made  on  it  by  Wm.  Sellers  &  Co. 

t  When  the  first  machine  was  tested,  a  steel  bar,  5  in.  in  diameter,  was  first  broken 
under  a  load  of  722,800  Ibs.,  and  then  a  single  horse-hair  was  tested',  and  the  machine 
gave  the  strength  (16  oz.)  of  this  as  accurately  as  a  small  spring-balance  which  was  used 
for  a  check.  Rep.  U.  S.  Test  Board,  vol.  n.  p.  1. 


330 


THE  MATERIALS  OF  CONSTRUCTION. 


plished  by  means  of  two  connected  metallic  sacks,  or  bags,  of  different  sizes, 
the  larger  one,  called  the  hydraulic  support,  receiving  the  full  force  trans- 
mitted through  the  specimen,  while  the  other  is  rigidly  held  upon  the 


primary  weighing-beam.  Thus  in  Fig.  265,  which  is  merely  a  schematic 
drawing,  the  load  is  received  on  the  hydraulic  support  shown  at  A,  and  the 
pressure  is  transmitted  by  means  of  the  enclosed  liquid  through  the  pipe  e 
to  the  smaller  sack  at  B,  which  being  rigidly  supported  by  the  heavy  cast- 
iron  frame,  G,  shown  in  section  above  and  below,  the  bearing-plate  c  is 
forced  downward,  causing  the  block  H  to  press  upon  the  primary  lever  C. 


TENSION  TESTS.  331 

This  is  then  transmitted  through  D  to  the  weighing-beam  E  and  the  indi- 
cator-arm F. 

In  place  of  knife-edges  on  the  weighing-beams,  thin  plates  of  steel  are 
employed,  these  being  rigidly  fastened  in  the  two  attached  beams.  These 
are  so  proportioned  as  to  bring  the  combined  bending  and  compression 
stresses  produced  in  them  well  within  their  elastic  limits.  While  these  offer 
absolutely  no  friction,  they  do  offer  some  elastic  resistance,  but  this  is  all 
allowed  for  in  calibrating  or  standardizing  the  machines.  The  weighing- 
beam  is  kept  in  balance  by  lowering  upon  it  various  weights  which  are  placed 
upon  the  several  poise-frames  which  are  suspended  from  this  weighing-beam. 
The  particular  manner  of  doing  this,  though  ingenious  and  peculiar  to  this 
machine,  is  not  essential  and  will  not  be  further  described  here.*  This  part 
of  the  apparatus  is  entirely  closed  by  a  glass  front,  and  it  is  never  necessary 
to  open  it,  the  weights  being  imposed  and  removed  from  outside,  and  the 
load  continuously  indicated  on  a  counter-cylinder  shown  in  Fig.  265  at  the 
left  end  of  the  indicator-arm  F. 

Passing  now  to  a  study  of  the  latest  form  of  the  machine  itself  and  its 
essential  details,  we  have  in  Fig.  266  a  view  of  the  200,000-lb.  testing- 
machine  made  for  Sibley  College  of  Cornell  University.  To  the  left  is  seen 
the  fixed  weighing-head,  containing  the  hydraulic  support,  and  to  the  right 
the  movable  straining -head, \  or  hydraulic  cylinder,  by  means  of  which  the 
load  is  applied  to  the  specimen  and  its  deformation  taken  up.  Both  of  these 
are  supported  and  kept  in  alignment  on  a  substantial  wrought-iron  girder- 
bed.  In  the  background  is  also  clearly  seen  the  wooden  case  containing  the 
scale,  with  some  of  the  levers  and  poise-frames  visible  through  its  glass  front, 
and  also  part  of  the  hydraulic  pump  which  supplies  the  straining-cylinder  at 
either  end,  according  as  the  machine  is  being  used  for  a  tension  or  a  com- 
pression test.  The  supply-  and  exhaust-pipes  are  seen  coining  up  through 
the  floor  at  the  end  of  the  bed,  and  connecting  with  the*  straining-head  by 
means  of  jointed  pipes  as  shown.  Rigidly  secured  to  the  weighing-head  by 
means  of  nuts  at  each  end  of  long  bearings,  one  on  each  side,  are  seen  the 
two  horizontal  reaction-bars,  on  which  are  cut  continuous  screw-threads. 
These  form  the  rigid  connection  between  the  fixed  weighing-head  and  the 
movable  straining-head,  through  which  they  pass  in  smooth  bearings  placed 
sufficiently  far  apart  to  allow  room — with  several  inches  of  clearance-space — 
for  two  large  abutment-nuts^  one  on  each  screw.  These  nuts  may  be  revolved 
simultaneously,  by  suitable  mechanism,  to  produce  motion  for  adjustment  of 
the  straining-head  in  either  direction  for  different  lengths  of  specimen. 

The  cut  shows  the  machine  ready  for  a  compression  test,  the  two  com- 
pression-platforms,  the  one  on  the  end  of  the  draw-bar  of  the  weighing-head, 

*  For  a  paper  by  J.  Sellers  Bancroft,  on  this  machine,  with  full  illustrations,  see 
Engr.  News  and  Am.  Machinist,  both  of  March  22,  1894. 

fin  this  term  the  word  "strain"  is  used  as  meaning  deformation  under  stress. 
Thus  the  elongation  (or  compression)  is  all  produced  by  the  moving  of  this  head  to  the 
right  or  left,  thus  producing  the  straining,  or  deforming,  of  the  specimen. 


334 


TEE  MATERIALS  OF  CONSTRUCTION. 


TENSION  TESTS.  335 

A  and  B,  are  respectively  the  cylinder  and  plunger  (more  properly  the  bear- 
ing-plates), or  blocks,  of  the  hydraulic  support,  which  is  thus  seen  to  be 
annular  in  the  actual  machine,  and  not  circular  as  the  one  shown  and 
described  in  connection  with  Fig.  205.  The  parts  marked  ^Vand  0  are  two 
annular  washers  that  clamp  the  edges  of  the  thin  brass  diaphragms  composing 
the  sack  to  the  bearing-block  L,  the  liquid  being  confined  between  these 
diaphragms,  as  also  already  described  in  connection  with  Fig.  265.  The  two 
plates  forming  this  closed  sack  are  not  soldered  together.  They  are  simply 
held  by  the  great  stress  in  the  bolts  which  bind  the  washers  N  and  0  so  as 
to  maintain  a  tight  joint  under  the  maximum  pressure.  The  pipe  forming 
the  communication  between  the  hydraulic  support  and  the  reducing-chamber 
of  the  scale  is  marked  R. 

The  draw-bar  heads  E  and  F  are  provided  with  a  number  of  external 
projections  or  spur-ribs,  £7,  extending  into  cavities  in  the  main  castings  A 
and  J3,  as  may  be  seen  in  the  case  of  the  head  E  and  the  main  casting  A. 
The  cavities  in  A  and  B  leave  between  them  an  equal  number  of  projections, 
F,  which  extend  back  into  the  cavities  between  the  ribs  U  on  the  draw-bar 
heads,  as  may  be  seen  in  the  case  of  the  head  F  and  the  main  casting  B. 
The  arrangement  of  these  ribs  and  cavities,  which  enables  a  machine  with  a 
single  hydraulic  support  to  be  used  both  for  tension  and  compression  tests, 
will  be  better  understood  from  Fig.  208,  in  the  right-hand  view  of  which 
this  is  made  perfectly  plain. 

The  manner  in  which  the  pull  on  the  draw-bar  is  transferred  by  the  ribs 
on  the  head  E  to  the  bearing-block  Z,  from  this  through  the  liquid-sack  over 
to  the  other  bearing-block  J/,  and  finally  from  this  to  the  ribs  on  the  main 
casting  B,  will  now  readily  be  understood,  and  it  will  also  be  seen  that  a 
push  on  the  draw-bar,  due  to  a  compression  test,  would  in  a  similar  manner 
be  transmitted  by  the  ribs  on  the  head  F  over  to  the  annular  bearing  J/, 
from  this  through  the  liquid  over  to  the  corresponding  bearing  L,  and  finally 
from  this  on  to  the  ribs  on  the  main  casting  A. 

Owing  to  supposed  internal  strains  and  stresses  in  the  diaphragms  of  the 
hydraulic  support,  it  has  been  found  necessary  to  put  about  50  or  CO  Ibs.  per 
square  inch  initial  pressure  on  the  same,  the  levers  of  the  scale  having  then 
first  to  be  balanced  by  means  of  a  suitable  weight  that  can  be  slid  along  a  rod 
attached  to  the  poise-frame  lever  before  beginning  a  test.  This  initial 
pressure  on  the  hydraulic  support  is  obtained  in  the  smaller  machines  by  the 
device  shown  in  Fig.  207,  while  in  larger  machines  a  very  complex  device  is 
used  to  get  the  requisite  pressure,  the  principle  of  this,  however,  being  essen- 
tially the  same.  The  device  as  here  shown  consists  of  a  large  flat  spring  S, 
attached,  in  a  manner  clearly  seen  in  the  figure,  to  the  projecting  ends  of  the 
reaction-bars,  and  forming  the  bearing  for  a  screw,  T,  secured  against  end 
motion  in  this  bearing  by  a  collar  attached  to  it  on  the  inside  of  the  spring, 
and  by  the  capstan-head  W  fastened  to  it  by  a  key  and  a  nut  in  the  cus- 
tomary manner  on  the  outside  of  the  spring.  This  screw  fits  into  a  tapped 
hole  in  the  end  of  the  draw-bar;  and  it  will  be  understood  that  if  the  capstan- 


336 


THE  MATERIALS  OF  CONSTRUCTION. 


TENSION  TESTS.  337 

head  be  turned  in  the  direction  of  the  arrow,  the  tendency  is  to  move  the 
draw-bar,  with  it  its  heads  and  the  whole  hydraulic  support,  away  from 
the  spring,  until  the  bearing-block  M  brings  up  against  the  ribs  on  the  main 
casting  B,  further  turning  producing  a  bending  of  the  spring  in  the  opposite 
direction.  The  resistance  of  the  spring  to  this  bending  is  then  transmitted 
through  the  screw  T,  the  end  of  the  draw-bar,  the  ribs  on  the  head  E,  the 
bearing-block  Z,  the  liquid,  and  finally  the  bearing  M  over  to  the  casting  B. 
This  condition  of  affairs  is  exactly  what  is  brought  about  before  beginning  a 
tension  test,  for  which  the  machine  is  supposed  to  be  represented  in  this 
figure.  A  sufficient  turning  of  the  capstan-head  in  the  direction  opposite  to 
that  indicated  by  the  arrow  will  similarly  pull  the  draw-bar,  etc.,  towards 
the  spring  8  until  the  cylinder  L  is  brought  up  against  the  ribs  of  the  main 
casting  A',  a  further  turning  bending  the  spring  towards  the  end  of  the 
draw-bar.  This,  with  its  consequences,  is  the  condition  of  affairs  brought 
about  before  beginning  a  compression  test. 

It  will  be  seen  that  the  spring  S  is  provided  with  a  stop,  to  match  a 
similar  stop  on  the  capstan-head  to  bring  up  against,  for  the  purpose  of 
limiting  the  motion  of  this  latter  in  either  direction,  the  pitch  of  the  screw 
T  being  so  selected  and  the  whole  device  so  fitted  up  that  the  determined 
amount  of  bending  of  the  spring  in  the  one  or  the  other  direction  will  pro- 
duce the  desired  amount  of  initial  pressure  on  the  diaphragm  of  the  hydraulic 
support.  The  total  possible  movement  of  the  hydraulic  support  in  its  cham- 
ber, between  the  attached  heads  A  and  B,  is  only  0.006  in.,  so  that  the 
maximum  movement  from  a  mean  position  is  only  0.003  in. 

Fig.  268  is  a  vertical  section  of  a  weighing-head,  in  which  the  hydraulic 
support  is  shown  in  its  most  improved  and  complete  form,  the  initial  pressure 
device  being,  however,  of  the  same  type  as  that  already  described.  It  will 
be  seen  that  the  annular  bearing-block  M  is  here  not  supported  on  the  draw- 
bar D  directly,  but  that  it  is  in  the  first  place  fixed  in  its  p'roper  relation  to 
the  bearing-block  Z,  independently  of  the  draw-bar,  by  two  annular  steel 
plates,  rigidly  clamped  in  the  usual  manner;  and  that  it  is  also  bolted  to 
another  large  annular  casting  F,  which  is  supported  on  the  draw-bar  in  the 
same  manner  as  the  bearing-block  L.  In  Addition  to  this  casting  V  there 
is  also  seen  another  annular  casting  X,  a  small  arc  of  the  circumference  of 
which  is  provided  with  gear-teeth  meshing  with  the  teeth  of  the  pinion  Y 
on  the  end  of  the  hand-lever  shaft  Z.  It  may  thus  to  a  limited  extent  be 
rotated  in  the  one  or  the  other  direction,  but  it  is  otherwise  confined  between 
the  main  casting  A  and  B,  and  also  to  be  centred  on  A  by  a  circular  tongue 
and  groove.  The  plates  X  and  V  are  on  the  figure  shown  to  be  in  contact, 
and  the  contact  surfaces  are  helicoidal  or  screw-shaped,  so  that  rotation  of 
JTin  one  direction  tends  to  force  them  apart,  and  to  bring  Fup  against  the 
ribs  of  the  casting  B,  while  rotation  of  X  in  the  opposite  direction  leaves  V 
with  a  little  play  between  X  and  B.  The  latter  of  these  conditions  is 
brought  about  by  the  operator  before  beginning  a  compression  test,  the 
former  before  beginning  a  tension  test.  The  purpose  of  this  arrangement  is 


THE  MATERIALS  OF  CONSTRUCTION. 


to  protect  the  diaphragm  of  the  hydraulic  support  from  the  great  shock  it 
would  otherwise  receive  by  the  sudden  release  of  the  stresses  on  the  various 
parts  of  the  weighing-head,  on  the  sudden  breaking  of  large  specimens  when 
a  powerful  recoil  of  the  draw-bar  occurs.  With  the  annular  anvil  V  set  up 
tight  against  B  by  the  annular  wedge  X,  the  energy  of  this  recoil  is  trans- 


mitted directly  over  to  the  main  casting  A  without  passing  through  the  liquid 
support  and  the  diaphragm,  on  which  an  exceedingly  high  pressure  would 
otherwise  be  produced,  which  if  frequently  repeated  would  finally  destroy  it. 
In  Fig.  269  is  shown  on  a  larger  scale  a  section  of  the  annular  hydraulic 
support  on  one  side  of  the  draw-bar  only,  which,  without  any  further  explana- 


TENSION  TESTS. 


339 


tion,  will  serve  to  give  a  clearer  idea  of  the  detailed  arrangement  of  the 
diaphragms  and  the  surrounding  parts,  and  also  the  manner  in  which  the 
pipe  7?,  which  forms  the  communication  between  the  hydraulic  support  and 


the  corresponding  reducing-chamber  on  the  scale,  is  attached. to  the  former. 
The  two  plates  which  form  the  sack  lie  flat  against  the  bearing-blocks, 
underlaid,  however,  by  connected  grooves,  their  edges  being  held  so  tight  by 


340 


THE  MATERIALS  OF  CONSTRUCTION. 


the  bolts  B  as  to  prevent  all  leakage.  The  plate  on  the  left  side  of  this 
sack  is  cut  away  and  spun  into  an  annular  pocket  in  the  auxiliary  block  PT, 
and  it  is  made  tight  to  it  by  running  in  a  solder.  To  this  auxiliary  block 
is  now  attached  the  connecting  pipe  R  as  shown.  This  pipe  is  first  soldered 
to  a  screw-plug  which  has  a  spherical  front  which  bears  on  the  conical  bottom 


FIG.  271.— The  Riehle-Marshall  Extensometer. 

of  the  opening  in  W>  so  that  by  screwing  up  hard  a  perfect  joint  is  made  by 
the  elastic  deformation  of  the  metal  at  the  surface  of  contact. 

In  Fig.  270  is  shown  the  form  given  to  this  machine  when  made  with  a 
capacity  of  100,000  Ibs. 

274.  Extensometers. — There  are  three  general  types  of  extensometers 
in  common  use,  viz.,  Double  Micrometer-screws  with  Electric  Contact; 


TENSION  TESTS. 


341 


Friction-rollers  with  Dial  Indicators;  and  Bauschinger's  Mirror  Apparatus. 
The  micrometer-screw  extensometer  was  developed  and  perfected  by  Mr. 
C.  A.  Marshall,  M.  Am.  Soc.  C.  E.,*  and  it  is  now  manufactured,  with  some 
improvements,  by  Riehle  Bros,  as  shown  in  Fig.  271.  The  essential  features 
of  all  these  extensometers  are : 

1.  Measurements  are  taken  on  opposite  sides  of  the  specimen,  between 
symmetrically  placed  points  on  rigid  collars  which  are  attached  to  the  speci- 
men by  screw-points  or  knife-edges  lying  in  two  transverse  planes  a  known 
distance  apart. 

2.  The  measurements  must  be  taken  to  the  nearest  To-jhro-  inch. 

3.  The  apparatus  must  be  removable  with- 
out releasing  the  load  on  the  specimen. 

In  the  Marshall  Instrument  the  collars 
are  open,  thus  enabling  them  to  be  removed, 
and  also  giving  to  them  a  sufficient  spring  to 
take  up  the  reduction  in  the  diameter  of  the 
specimen  as  it  elongates.  The  elongations 
are  read  on  micrometer-screws  to  0.0001 
inch,  the  contact  being  determined  by  the 
ringing  of  an  electric  bell  on  the  closing  of 
a  circuit  by  the  contact.  With  a  low  but 
constant  current  this  contact- distance  is 
found  to  be  constant  within  the  limit  of  read- 
ing given  above,  f  Both  screws  are  read  after 
each  increment  of  loading,  and  the  average 
movement  taken  as  the  stretch  of  the  speci- 
men. This  is  a  most  excellent  and  delicate 
instrument  and  is  very  largely  used.  It  has 
the  advantage  of  a  more  positive  and  direct 
measurement  of  the  deformation  of  the  speci- 
men than  either  of  the  other  forms. 

The  extensometer  having  friction-rollers 
with,  dial-indicators,  shown  in  Fig.  272,  is  a 
modification  of  one  of  Bauschinger's  forms, 
as  made  and  used  by  the  author.  J  It  operates 
by  means  of  two  axles,  having  friction-rollers 
at  one  end  and  a  vernier-needle  at  the  other 
which  moves  over  a  graduated  dial.  The 
friction-roller  is  just  0.5  inch  in  circumference,  and  the  dial  is  graduated  to 
500  divisions.  The  vernier  on  the  end  of  the  needle  reads  readily  to  0.1  of 

*  A  brilliant  young  engineer,  a  friend  and  college-mate  of  the  author's,  who  lost  his 
life  in  the  great  Johnstown  flood,  1889. 

f  By  using  a  resistance  relay  in  the  circuit  a  strong  current  may  be  made  to  pass 
through  the  bell,  and  a  weak  one  through  the  contact  points. 

t  Manufactured  by  Mahn  &  Co.  of  St.  Louis,  Mo. 


FIG.    272,— The  Author's    Exten- 
someter. 


342  THE  MATERIALS  OF  CONSTRUCTION. 

a  division,  thus  giving  readings  to  0.0001  inch.  The  collars  are  attached 
by  three  screws,  and  removed  by  opening  them  by  a  hinge  movement. 
One  of  the  screws  has  a  spring  bearing  in  the  collar  to  take  up  the  shrink- 
age of  the  specimen  when  under  stress. 

The  friction-rollers  are  actuated  by  means  of  two  arms  which  have  a  spring 
bearing  upon  them,  the  opposite  ends  being  rigidly  attached  to  the  opposite 
collar  in  each  case.  Thus  while  the  needles  move  in  the  same  direction  any 
bending  of  the  specimen,  or  angular  movement  of  the  collars  with  respect 
to  each  other,  is  eliminated  in  the  mean  of  the  two  readings,  the  same  as 
with  the  Marshall  apparatus.  The  needles  are  delicately  mounted  so  as  to 
have  very  little  friction,  and  experience  shows  that  the  friction-contact  is 
entirely  reliable. 

The  advantages  of  this  form  of  extensometer  are: 

1.  It  shows  by  its  movements  the  deforming  action  of   the  specimen, 
which  is  a  great  advantage  for  students. 

2.  It  is  equally  suited  to  measure  large  deformations  beyond  the  elastic 
limit  as  it  is  to  measure  the  extremely  small  movements  inside  that  limit. 

3.  It  is  equally  adapted  to  compressive  and  tensile  tests. 


kl 


^M& 


FIG.  273. — Diagrammatic  Plan  of  Bauscbinger's  Mirror  Extensometer. 


4.  It  is  adapted  to  all  lengths  of  specimens  by  simply  changing  the  side 
arms,  several  pairs  of  which  go  with  the  instrument.* 

5.  On  releasing  the  load  it  shows  the  permanent  set  without  any  manip- 
ulation. 

6.  It  never  needs  to  be  touched  by  the  observer  during  a  test,  which  is  a 
great  advantage  in  making  such  delicate  measurements. 

7.  After  passing  the  elastic  limit,  and  under  a  given  constant  load,  the 
continued  movement  of  the  needle  indicates  the  time-effect  of  such  loads 
and  when  such  cold-flowing  has  practically  ceased. 

If  the  specimen  should  unexpectedly  break  with  the  apparatus  on,  no 
great  harm  results.  At  most  some  of  the  clamping-screws  may  be  bent,  but 
these  cost  little  to  renew. 

*  The  author  has  used  it  successfully  for  observing  the  effects  of  moving  loads  on 
bridge  members,  with  arms  five  feet  long,  covered  with  thin  rubber  at  their  roller  ends, 
and  specially  made  U-shaped  clamps  instead  of  collars. 


TENSION  TESTS. 


343 


Bauschingers  Mirror  Apparatus  is  shown  in  Figs.  273  and  274.  The 
specimen  is  clamped  at  two  points,  as  shown  at  (#),  Fig.  274,  and  at  a  and  #, 
Fig.  273.  The  stretch  of  the  specimen  is  fully  represented  by  the  turning 
•of  the  friction-rollers  rl  and  ra,  these  being  rigidly  attached  to  the  mirrors 
w,  and  mn  through  the  arms  al  and  «a.  The  screws  set  back  of  the  mirrors 


FIG.  274.— Buuschingcr's  Mirror  Exteusometer  Apparatus.  FIG.  275. 

are  used  to  adjust  them  to  a  zero-reading  on  the  scale,  which  is  reflected  into 
telescopes  as  shown  in  Fig.  273. 

For  simply  observing  stretch  for  the  purpose  of  detecting  the  elastic  limit 
with  reasonable  accuracy,  the  Paine  extensometer,  Fig.  275,*  may  be  used 

*  Designed  by  W.  II.  Paine,  M.  Am.  Soc.  C.  E.,  and  used  by  him  for  finding  the 
•elastic  limit  of  the  steel  wire  used  on  the  New  York- Brooklyn  suspension  bridge. 
Made  now  by  Richie  Bros. 


342  THE  MATERIALS  OF  CONSTRUCTION. 

a  division,  thus  giving  readings  to  0.0001  inch.  The  collars  are  attached 
by  three  screws,  and  removed  by  opening  them  by  a  hinge  movement. 
One  of  the  screws  has  a  spring  bearing  in  the  collar  to  take  up  the  shrink- 
age of  the  specimen  when  under  stress. 

The  friction-rollers  are  actuated  by  means  of  two  arms  which  have  a  spring 
bearing  upon  them,  the  opposite  ends  being  rigidly  attached  to  the  opposite 
collar  in  each  case.  Thus  while  the  needles  move  in  the  same  direction  any 
bending  of  the  specimen,  or  angular  movement  of  the  collars  with  respect 
to  each  other,  is  eliminated  in  the  mean  of  the  two  readings,  the  same  as 
with  the  Marshall  apparatus.  The  needles  are  delicately  mounted  so  as  to 
have  very  little  friction,  and  experience  shows  that  the  friction-contact  is 
entirely  reliable. 

The  advantages  of  this  form  of  extensometer  are : 

1.  It  shows  by  its  movements  the  deforming  action  of   the  specimen, 
which  is  a  great  advantage  for  students. 

2.  It  is  equally  suited  to  measure  large  deformations  beyond  the  elastic 
limit  as  it  is  to  measure  the  extremely  small  movements  inside  that  limit. 

3.  It  is  equally  adapted  to  compressive  and  tensile  tests. 


^ 
FIG.  273. — Diagrammatic  Plan  of  Bauschinger's  Mirror  Extensometer. 

4.  It  is  adapted  to  all  lengths  of  specimens  by  simply  changing  the  side 
arms,  several  pairs  of  which  go  with  the  instrument.* 

5.  On  releasing  the  load  it  shows  the  permanent  set  without  any  manip- 
ulation. 

6.  It  never  needs  to  be  touched  by  the  observer  during  a  test,  which  is  a 
great  advantage  in  making  such  delicate  measurements. 

7.  After  passing  the  elastic  limit,  and  under  a  given  constant  load,  the 
continued  movement  of  the  needle  indicates  the  time-effect  of  such  loads 
and  when  such  cold-flowing  has  practically  ceased. 

If  the  specimen  should  unexpectedly  break  with  the  apparatus  on,  no 
great  harm  results.  At  most  some  of  the  clamping-screws  may  be  bent,  but 
these  cost  little  to  renew. 

*  The  author  has  used  it  successfully  for  observing  the  effects  of  moving  loads  on 
bridge  members,  with  arms  five  feet  long,  covered  with  thin  rubber  at  their  roller  ends, 
and  specially  made  U-shaped  clamps  instead  of  collars. 


TENSION  TESTS. 


3413 


Bauschinger's  Mirror  Apparatus  is  shown  in  Figs.  273  and  274.  The 
specimen  is  clamped  at  two  points,  as  shown  at  (£),  Fig.  274,  and  at  a  and  b, 
Fig.  273.  The  stretch  of  the  specimen  is  fully  represented  by  the  turning 
•of  the  friction-rollers  r,  and  ra,  these  being  rigidly  attached  to  the  mirrors 
mv  and  m,  through  the  arms  al  and  aa.  The  screws  set  back  of  the  mirrors 


FIG.  274.— Bauschinger's  Mirror  Exteusometer  Apparatus.  FIG.  275. 

are  used  to  adjust  them  to  a  zero-reading  on  the  scale,  which  is  reflected  into 
telescopes  as  shown  in  Fig.  273. 

For  simply  observing  stretch  for  the  purpose  of  detecting  the  elastic  limit 
with  reasonable  accuracy,  the  Paine  extensometer,  Fig.  275,*  may  be  used 

*  Designed  by  W.  II.  Paine,  M.  Am.  Soc.  C.  E.,  and  used  by  him  for  finding  the 
•elastic  limit  of  the  steel  wire  used  on  the  New  York-Brooklyn  suspension  bridge. 
Made  now  by  Richie  Bros. 


344 


THE  MATERIALS  OF  CONSTRUCTION. 


with  advantage.  Its  multiplication  is  usually  made  about  20  to  1,  and  it 
may  be  read  by  vernier  to  0.0001  inch,  though  it  is  usually  made  to  read 
only  to  0.001  inch.  This  instrument  has  also  been  used  to  obtain  the  stretch 
of  bridge  members  under  moving  loads.  As  it  measures  stretch  on  only  one 
side  of  the  specimen,  its  indications  must  not  be  accepted  as  absolute, 
especially  inside  the  elastic  limit,  while  its  capacity  is  very  small  beyond  the- 
elastic  limit. 

A  very  simple  and  inexpensive  apparatus  which  may  be  made  to  give 
excellent  results  is  shown  in  Fig.  276.     If  care  be  taken  to  secure  a  practi- 


FIG.  276.—  Extensometer  used  in  Yorkshire  College,  Leeds.     (From  Engineering,  Sept. 

11,  1896.) 

cally  constant  length  of  the  short  arm  of  the  indicator,  and  if  the  legs  of  the 
main  frame  which  carry  the  graduated  arc  are  equally  flexible,  fairly  accu- 
rate readings  can  be  obtained. 

275.  Autographic  Stress-diagram  Appliances. — These  fall  into  two  gen- 
eral classes: 

1.  Those  in  which  the  load  coordinate  is  recorded  through  a  movement 
of  the  poise  on  the  weighing-beam. 

2.  Those  in  which  the  load  coordinate  is  recorded  through  the  lifting  of 
the  weighing-beam  against  the  increasing  resistance  of  a  calibrated  spring 
attached  to  its  free  end. 

The  deformation  coordinate  is  in  all  cases  multiplied  either  by  levers  or 
by  the  principle  of  the  cone-pulley.  The  paper  is  usually  attached  to  a 
cylinder,  although  it  has  sometimes  been  attached  to  a  plane  board.  The 
pencil  usually  moves  in  a  straight  line,  indicating  one  of  the  two  coordinates, 
while  the  cylinder  (or  board)  moves  to  register  the  other  function,  and  it 
matters  not  which  of  the  two  movements  is  made  by  the  deformation  of  the 


TENSION  TESTS. 


345 


specimen  and  which  by  the  increasing  load.  The  location  of  the  paper  and 
its  mounting  is  a  matter  of  convenience  simply.  The  cords  (or  wires)  which 
are  to  transmit  the  stretch  of  the  specimen  must  form  a  pair,  symmetrically 
placed  on  opposite  sides  of  the  specimen;  they  must  be  attached  to  one  collar 
and  pass  through  pulleys  similarly  placed  on  the  other.  They  should  then 
pass  off  in  a  plane  at  right  angles  to  the  specimen  *  and  connect  with  the 
ends  of  an  "  evener  "  (lever),  to  the  centre  of  which  is  attached  the  single 
cord  which  passes  either  to  the  pencil-holder  or  to  the  cylinder  which  carries 
the  paper.  If  cords  are  used,  they  should  be  such  as  do  not  stretch  appreci- 
ably for  such  changes  of  stress  as  occur  in  them  during  the  test. 

One  method  of  mounting  these  parts  is  shown  in  Fig.  256  (Olsen's),  and 
another  form  in  Fig.  258  (Richie's).  In  both  cases  the  pencil  is  moved  by 
the  poise  by  a  reducing-gear,  and  the  cylinder  is  moved  by  the  deformation 
of  the  specimen  by  a  multiply  ing-gear. 

Figs.  277  and  278  show  two  improvised  forms  of  autographic  diagram 


Automatic  Strain  Diagram 
Apparatus 

for 
Tension    Tests, 


FIG.  277. 

apparatus  which  the  author  devised  and  had  attached  to  his  100,000-lb. 
hydraulic  testing-machine,   for   tension   and   punching   tests   respectively, 

*  This  is  necessary  in  order  that  the  stretch  of  the  specimen  may  be  fully  repre- 
sented in  the  shortening  up  of  the  cord.  The  eoi^s  should  therefore  be  attached  to  the 
moving  end  of  the  specimen. 


346 


THE  MATERIALS   OF  CONSTRUCTION. 


Here  the  .pencil  is  moved  by  means  of  a  fine  wire  which  coils  over  the  small 
spindle  to  which  the  poise  driving-pulley  is  attached,  while  the  cylinder  is 


Automatic  Strain  Diagram 
Apparatus 

for 
Shearing    Tests . 


FIG.  278. 

turned  by  the  cord  from  the  specimen  runs  upon  a  small  dram  at  top.* 
This  cord  is  kept  taut  by  means  of  a  small  plumb-bob.  The  clamp-screws 
in  the  collars  are  set  so  as  to  take  hold  of  a  square  or  rectangular  specimen 
as  well  as  a  round  one.  The  second  form  was  made  for  a  series  of  punching 
tests  of  steel  plates. 

A  great  defect  of  all  the  autographic  appliances  given  above  is  that  they 
do  not  readily  give  the  last  end  of  the  curve  after  passing  the  maximum 
load,  although  they  would  do  this  if  the  poise  should  be  run  back  so  as  to 
keep  the  beam  in  balance  at  all  times.  This  is  a  difficult  feat  with  both  the 
hand-  and  the  electrically-controlled  movement  of  the  poise,  and  the  result  is 
that  this  part  of  the  diagram  is  usually  worthless.  ^ 

In,  the  Gray  Extensometer  Apparatus^  however,  Fig.  279,  this  part  of 
the  curve  is  obtained  perfectly,  for  the  weighing-beam  is  at  all  times  in 
perfect  balance,  since  it  pulls  upon  a  calibrated  spring.  Here  the  pencils 
are  moved  at  two  rates  of  speed  by  the  deformation  of  the  specimen,  and  the 
cylinder  is  turned  by  the  lifting  or  dropping  of  the  weighing-beam.  The 

*  This  cord  should  lead  off  from  the  specimen  at  the  upper  (fixed)  cross-head  instead 
of  from  the  lower  one.     The  drawing  is  erroneous  in  this  particular, 
f  Designed  by  Prof.  Thos.  Gray,  and  manufactured  by  Riehle  Bros. 


TENSION   TESTS. 


347 


348 


THE  MATERIALS   OF  CONSTRUCTION. 


ong  trussed  lever  at  top  gives  a  movement  to  one  of  the  pencils  of  from  one 
to  two  times  the  actual  deformation  between  the  collars,  while  the  other 
trussed  lever  may  give  to  the  other  pencil  a  movement  from  one  hundred  to 
five  hundred  times  the  actual  relative  movement  of  the  collars,  depending 
in  each  case  on  the  link  connections  which  are  made  preparatory  to  start- 
ing the  test.  Furthermore,  both  pencils  operate  inside  the  elastic  limit  and 
some  distance  beyond,  when  the  one  moving  more  rapidly  is  automatically 
thrown  out  of  gear,  while  the  other  pencil  proceeds  to  record  the  complete 
diagram  on  the  smaller  scale.  The  result  is  a  double  stress  diagram,  such 
as  shown  in  Fig.  5.  The  diagrams  shown  in  Fig.  280  have  been  photo- 
graphically reduced  directly  from  autographic  diagrams  made  by  this  appli- 


Fro.  280. — Tension-stress  Diagrams  of  Low  Carbon-steel  automatically  recorded  by  the 
Gray  Apparatus.     (Made  by  Prof.  Gray  for  the  author.) 

ance  for  the  author  b}^  Prof.  Gray  himself.     They  do  not  extend  beyond  the 
yield-point  stage  of  the  test. 

Mr.  Olserfs  new  Micrometer  Autographic  Attachment  forms  a  supplement 
to  his  general  stress-diagram  apparatus,  for  the  purpose  of  making  a  diagram 
inside  of  and  somewhat  beyond  the  elastic  limit,  in  which  the  stretch  of  the 
specimen  is  magnified  five  hundred  times.  He  accomplishes  this  by  revolving 
the  drum  one  hundred  times  as  fast  inside  the  elastic  limit  as  is  done  beyond 
that  limit,  the  stretch  of  the  specimen  here  being  greatly  multiplied  by  a 
micrometer-screw  and  its  accompanying  gearing  shown  in  Fig.  281.  When- 


TENSION  TESTS. 


349 


ever  the  collars  separate,  the  lower  pair  of  fingers  (being  weighted)  drop 
with  the  lower  collar  and  so  break  an  electric  spring-contact  shown  on  the 
left  of  Fig.  281,  which  sets  in  motion  both  the  drum  carrying  the  paper  (not 
shown  here)  and  the  micrometer-screw  and  its  gearing,  which  at  once  closes 
the  circuit  by  raising  the  outer  end  of  the  lever  to  which  the  spring-contact 


is  attached.  A  very  large  circumferential  motion  can  thus  be  obtained  for 
a  very  small  movement  of  collars  (500  to  1),  and  this  can  be  conveyed  by  a 
positive  connection  to  the  dram  of  the  autographic  apparatus.  When  the 
elastic  limit  has  been  passed  this  part  of  the  apparatus  is  thrown  out  of  gear, 
the  drum  set  back  to  its  proper  position  under  the  pencil  for  the  small-scale 


350 


THE  MATERIALS  OF  CONSTRUCTION. 


diagram  (deformation  5  to  1),  and  the  test  proceeds  to  its  completion  at  the 
final  rupture  of  the  specimen.  The  poise  is  moved  either  forward  or  back- 
ward at  pleasure  by  making  the  proper  electric  connections,  or  both  these 
connections  can  be  made  at  once,  in  which  oase  the  poise  moves  forward  when 
the  beam  is  up,  and  backwards  when  it  is  down.  The  last  part  of  the  diagram 


can  thus  be  obtained.     The  entire  machine,  with  both  the  large-  and  the 
small-scale  diagram  apparatus,  is  shown  in  Fig.  282. 

276.  Micrometer-callipers. — In  Figs.  283,  284,  and  285  are  shown  three 
forms  of  micrometer-callipers,  one  or  more  of  which  are  necessary  for  accu- 


TENSION  TESTS. 


351 


352 


TEE  MATERIALS  OF  CONSTRUCTION. 


rately  measuring  the  dimensions  of  test  specimens,  The  form  shown  in  Fig. 
283*  spans  8  inches;  that  shown  in  Fig.  284  spans  2  inches,  and  that  in 
Fig.  285  spans  2£  inches,  all  of  them  reading  to  0.0001  inch.  The  advan- 
tage of  the  last  form  is  that  one  may  be  set  for  the  width  and  the  other  for 
the  thickness  of  plates,  thus  saving  much  running  back  and  forth  of  the 
micrometer-screw. 

277.  Gauging-implements. — It  is  common  to  lay  off  the  test  specimen 
into  1-inch  divisions  either  by  scratch-awl  or  centre-punch  marks.     For  the 


FIG.  286. 


former  (used  on  plate  specimens)  the  laying-off  gauge  shown  in  Fig.  286  is 
used,  and  for  the  latter  (used  on   round  specimens)  the   double-pointed 


FIG.  287. 

centre-punch  shown  in  Fig.  287  is  most  convenient.      Some  such  instru- 
ments are  essential  to  accurate  work,  and  they  also  are  great  time-savers. 

*  Designed  by  Prof.  Sweet  and  made  by  the  Syracuse  Twist  Drill  Co.,  Syracuse, 

N.  Y. 


CHAPTER   XVI. 
COMPRESSION  TESTS. 

278.  Objects  of  Compression  Tests. — While  tension  tests  are  made  for  the 
purpose  of  determining  many  of  the  more  significant  mechanical  properties 
of  the  malleable  metals,  compression  tests  are  made  to  determine  resistance 
to  compression  alone.     In  Chapter  III  it  was  shown  that  the  materials  of 
construction  divide  themselves  into  two  general  classes  with  respect  to  their 
manner  of  failure  in  compressive  tests,  these  two  classes  being  called  plastic 
or  viscous  materials,  such  as  the  malleable  metals,  and  brittle  or  comminuible 
materials,  such  as  cast  iron,  stone,  brick,  etc. 

When  testing  plastic  materials  in  compression  the  "  apparent  elastic 
limit"  must  be  regarded  as  the  ultimate  strength;  and  since  this  limit  in 
compression  is  in  nearly  all  cases  the  same  as  it  is  in  tension,  it  is  commonly 
taken  as  the  same,  and  no  compression  tests  are  made  on  such  materials  except 
when  made  up  into  fall-sized  columns.  The  compression  tests  of  these  are 
known  as  "  tests  of  columns,"  rather  than  "  compression  tests  "  of  that 
material. 

Brittle  materials  are  tested  in  compression  to  determine  their  resistance 
to  crushing. 

279.  Compression-test  Specimens. — In  the  case  of  metals  the  test  speci- 
mens can  be  turned  or  shaped  accurately,  but  in  the  case  of  stone,  cement, 
concrete,  brick,  etc.,  it  is  not  practicable  to  obtain  perfectly  true  specimens, 
and  hence  some  suitable  provision  must  be  made  for  these  when  placing  them 
in  the  testing-machine.      For  such  materials  the  form  of  specimen  hitherto 
almost  universally  employed  has  been  that  of  the  cube.     In  Chapter  III  it 
was  shown  that  this  form  is  too  short  to  give  a  normal  failure;  that  the 
length  in  the  direction  of  the  applied  load  should  be  at  least  1£  times  the 
least  .lateral  dimension.     It  is  probable,  however,  that  compression  tests  will 
continue  to  be  made  on  cubical  forms,  for  the  reason,  that  the  results  may 
thus   be  comparable    with    those   hitherto   obtained   and   published.     The 
general  relation  between  the  strength  of  cubes  and  of  prisms  of  various  ratios 
of  height  to  least  breadth,  for  sandstone,  is  shown  in  Fig.  17,  Chapter  III. 

While  perfectly  true  and  parallel  surfaces  cannot  usually  be  obtained, 
they  should  be  made  as  nearly  so  as  possible.  This  can  be  done  at  a  small 
cost  if  stone-grinding  works  are  at  hand,  or  if  such  a  special  grinding-machine 
is  available  as  that  shown  in  Fig.  288. 

353 


354 


THE  MATERIALS  OF  CONSTRUCTION. 


The  test  specimen  should  be  very  nearly  prismatic,  since  when  the  sides 
protrude  much  beyond  the  bearing-surfaces  the  specimen  is  strengthened  as 


shown  in  Fig.  18. 


/0000 


1 

7000 


FIG.   288.  —  An  Abrasion  Testing- 
machine. 


1 

3000 

FIG.  289.— Showing  the  Effect  of  Bed- 
ding on  the  Strength  of  Sandstone. 
(Inst.  Civ.  Engrs.,  vol.  cvn.) 

280.  Bedding  the  Specimen  in  the  Testing-machine. — If  the  specimen 
has  not  true  and  parallel  beds,  it  is  necessary  to  embed  the  specimen  in 
plaster  of  paris.  This  is  done  by  inserting  sized  paper  between  the  plaster  of 
paris  and  the  specimen  to  prevent  the  absorption  of  water  by  the  specimen, 
which  invariably  weakens  it  if  it  has  a  high  absorbing  capacity.  A  small 
load  is  brought  upon  the  specimen  while  the  plaster  beds  are  soft,  and  this 
is  left  on  for  some  ten  minutes  or  longer,  till  the  plaster  has  hardened,  when 
the  test  proceeds  to  failure.  Great  care  must  always  be  taken  to  put  the  test 
specimen  accurately  in  the  axis  of  the  testing -mad Line.  Compression  tests 
probably  more  often  give  erroneous  results  from  not  having  done  this  than 
from  any  other  cause. 

If  the  specimen  has  true  and  parallel  beds,  then  it  may  be  placed  directly 
between  steel  plates,  or  between  the  machine  cross-heads,  if  these  are  true 
and  smooth.  Or  single  thicknesses  of  tar-board  may  be  employed.  In  any 
case  no  bedding  material  must  be  used  which  will  flow,  like  lead,  or  spread, 
like  wood,  when  the  load  comes  on.  This  causes  the  specimen  to  split  up 
and  to  fail  in  detail.  (See  Fig.  289.) 

An  infallible  test  of  x>roper  bedding  and  placing  in  the  testing-machine 
is  the  manner  of  failure  of  the  specimen.  If  it  spalls  off  on  the  sides 
(especially  if  it  spalls  mostly  on  one  side)  before  final  crushing  down,  some- 


COMPRESSION  TES 


355 


thing  is  wrong.    It  should  spall  very  little,  and  should  crush  down  suddenly, 
with  a  great  explosive  sound,  and  fly  over  the  room. 

An  adjustable  bearing-plate  at  one  or  at  both  ends  of  the  specimen  is 
desirable,  bat  not  strictly  necessary  if  care  be  taken  to  secure  in  other  ways 
a  true  initial  bearing. 

281.  Compression-test  Machines. — The  universal  machines  shown  in  Figs. 
25(5,  257,  258,  259,  2GO,  266,  and  270  are  all  adapted  to  the  making  of 
compression  tests  as  well  as  tests  in  tension.    In  Fig.  377  is  shown  a  machine 
for  compression  (cement)  tests  only,  and  the  author  has  had  constructed  a 
machine  for  testing  timber  columns,  with  a  capacity  of  1,000,000  Ibs.,  which 
works  in  compression  only,  bat  in  general  all  the  compression  machines  used 
in  America  are  of  the  universal  type. 

282.  Compressometers. — Since  compression-test  specimens  are  generally 
very  short,   the  ordinary  appliances  used  in  tension  tests  for  measuring 


FIG.  290. 

deformations  cannot  be  employed.  In  Fig.  290  a  very  convenient  com- 
pressometer  is  shown,  which  is  adjustable  to  varying  heights  of  specimen  by 
moving  the  geared  pair  of  screws,  and  to  specimens  of  excessive  height  by 
introducing  new  sets  of  screw-stems.  The  bearing-points  are  in  pairs, 
mounted  on  rockers,  so  that  any  unsymmetrical  movement  is  provided  for  and 
eliminated.  It  reads  to  y^/nro  inch  by  electric  contact  at  the  right  end, 
under  the  set-screw  there.  The  deformation  of  the  specimen  breaks  this 
contact,  and  by  turning  the  micrometer-screw  the  contact  is  made,  this  being 
indicated  by  the  ringing  of  a  magneto-bell. 

For  large  specimens  a  form  like  that  of  Prof.  C.  Bach,  Fig.  291,  may 
be  used.*  This  measuring  device  consists  of  two  rings,  AA  (on  top)  and  BB 
(below),  each  of  which  is  fastened  to  the  specimen  by  means  of  four  screws, 

*  The  description  here  given  is  taken  from  Zeits.  d.  Ver.  Deutscher  Ingenieure,  April 
27,  1895. 


356 


THE  MATERIALS  OF  CONSTRUCTION. 


PIG.  291.— Bach's  Apparatus  for  Compression  Tests  of  Concrete  Columns  10  in.  diam- 
eter and  40  in.  long. 


COMPRESSION  TESTS.  357 

being  at  right  angles  to  each  other  at  any  convenient  distance  apart.  (The 
apparatus  shown  in  the  figure  was  used  on  concrete  cylinders  10  inches  in 
diameter  and  40  inches  long,  the  rings  being  30  inches  apart.) 

The  measuring  apparatus  is  shown  on  the  right.  If  a  compression  of  the 
test  specimen  occurs,  the  upper  terminal  point  of  the  rod,  C\  which  length 
remains  the  same,  will  move  upwards  a  distance  equal  to  the  distortion  of 
the  specimen,  thus  causing  the  lever  DEF  to  turn  around  its  axis  at  E,  and 
to  carry  along  with  it,  by  the  small  metallic  thin  ribbon  fastened  on  its  seg- 
mental  end  F,  the  axis  6r,  on  which  the  indicator  is  fastened,  which  latter 
runs  along  the  arc  graduation.  The  indicator  is  not  pointed  at  the  end,  but 
flat,  and  upon  it  is  an  index-line,  as  may  be  seen  in  the  drawing.  The  ratio 
is  made  so  that  1  mm.  compression  of  the  test  specimen  equals  300  mm. 
distance  on  the  arc  scale.  Since  this  can  be  read  to  -^  mm.,  the  distortion 
of  the  measured  distance  can  be  read  to  ^F  mm-  The  only  new  feature 
of  this  instrument  is  the  use  of  the  thin  metallic  ribbon  in  place  of  gearing. 

The  disadvantage  of  employing  a  rack  and  pinion  was  that  the  loads  had 
to  be  varied  by  loading  and  unloading;  the  least  lost  motion  would  produce 
serious  errors.  Furthermore,  the  transmission  proportion  is  dependent  on 
the  form  of  the  tooth,  for,  being  obliged  to  make  the  teeth  so  very  small,  we 
cannot  depend  on  forming  them  sharp  enough  to  maintain  a  constant  trans- 
mission proportion.* 

There  should  always  be  two  such  measuring  instruments,  set  opposite 
each  other,  as  shown  in  the  general  view  on  the  left.  By  this  method  the 
measurement  of  the  deformation  takes  place  at  two  diametrically  opposite 
points,  the  mean  of  the  two  readings  being  used.f 

For  measuring  given  percentages  of  compression  deformation  of  wood 
blocks  of  varying  thicknesses,  for  instance,  the  author  devised  the  apparatus 
shown  in  Fig.  292.  Here  a  metal  point,  attached  to  a  sleeve,  moves  on  an 
adjustable  inclined  arm,  so  bent  that  the  point  moves  on  a  fine  through  the 
hinge  in  the  plane  of  the  flat  base  of  the  apparatus.  The  making  of  the 
contact  at  the  point  rings  an  electric  bell,  and  the  free  movement  of  this 
point  is  interrupted  by  spring  stops  at  such  percentages  of  distortion  as  are 
to  be  observed  (with  the  U.  S.  timber  tests,  in  compression  across  the  grain, 
these  observed  deformations  were  3  per  cent  and  15  per  cent  of  the  thick- 
ness of  the  block).  For  a  specimen  of  any  height  it  is  only  necessary  to 
move  the  point  to  its  outer  limit,  raise  it  into  contact  with  the  upper  com- 
pression-head of  the  machine,  and  tighten  the  thumb-nut.  Then  slide  the 
point  back  to  thb  first  stop  and  proceed  to  load  the  specimen.  When  the 
bell  rings  note  the  load  for  that  limit,  and  slip  the  point  to  the  next  stop, 
etc. 

*  Where  simple  friction  of  a  bar  on  a  rolling  pinion  is  relied  on  to  move  the  indicator- 
needle,  great  care  must  be  exercised,  especially  when  loads  are  applied  or  released  sud- 
denly. 

f  These  instruments  are  made  by  C.  Klebe  of  Munich,  Germany. 


358 


THE  MATERIALS  OF  CONSTRUCTION. 


Weighing   Table  of  Testing   Machine . 

FIG.    292. — Compressometer  designed   by   the   Author  to  Indicate   two   Conventional 
Limits  of  Deformation  (3$  and  15$)  of  Wood  Blocks  when  Tested  Across  the  Grain. 


FIG.  293. — Tetmajer's  Compressometer  for  very  short  Specimens  Tested  in  a  Horizontal 
Machine.     (Zurich  Laboratory  Communications,  vol.  iv.) 


COMPRESSION  TESTS.  359 

283.  Tetmajer's  Apparatus  for  Short  Specimens. — In  Fig.  293  is  shown 
Prof.   Tetmajer's  apparatus  for  measuring  the  deformation  of  very  short 
specimens.*     It   is   used   in  a  horizontal    (Werder)    machine,   and    stands 
upright  as  in  the  figure.     The  compression  of  the  specimen  is  taken  up  on  a 
micrometer-screw  which  operates  on  the  short  arm  of  the  indicator,  the  long 
arm  of  which  actuates  the  upper,  balanced,  horizontal  lever,  thus  bringing  it 
to  its  zero  position  as  shown  by  graduation  lines  on  its  left-hand  end,  and  on 
the  adjoining  fixed  portion  of  the  frame.     Because  of  the  measurements 
being  taken  on  one  side  only,  and  that  a  long  distance  from  the  specimen, 
the  readings,  while  giving  true  relative  motion,  would  probably  not  be  true 
absolutely.     Tetmajer  used  it  mainly  to  determine  elastic  limits.     His  read- 
ings were  taken  to  0.0001  inch,  and  great  care  was  taken  in  centring  the 
specimen  in  the  testing-machine. 

284.  Compression  Tests  of  Columns,  f — Since   the   strength   of   a   long 
column  consists  in  its  resistance  to  bending,  rather  than  in  its  resistance  to 
crushing,  it  follows  that  the  strength  of  a  straight  column  is  a  function  of — 

1.  The  elastic  rigidity  (modulus  of  elasticity)  of  the  material,  E. 

2.  The  ratio  of  its  length,  ?,  to  the  rigidity  function  of  its  cross-section, 

which  is  the  radius  of  gyration,  r,  that  is,  — . 

3.  The  character  of  its  end  bearings  as  to  their  tendency  to  hold  the 
column  to  its  original  position,  and 

4.  The  eccentricity  of  the  loading. 

For  a  straight  column,  symmetrically  loaded,  supported  at  its  gravity 

axis,  and  so  as  to  be  perfectly  free  to  bend,  and  for  a  ratio  of  —  sufficiently 

large,  it  is  shown  in  works  on  mechanics  (and  in  the  author's  "  Modern 
Framed  Structures  ")  that  Eider's  Formula  gives  the  strength  of  the 
column.  This  formula  is 


where p  =  ultimate  strength  of  the  column,  in  pounds  per  square  inch; 
E  —  modulus  of  elasticity,  in  pounds  per  square  inch; 
I  =  length  of  the  column  between  the  pivot-bearings,  in  inches; 

*  Described  in  Tetmajer's  Communications,  vol  iv.  (1890). 

f  It  does  not  fall  within  the  province  of  this  work  to  enter  into  a  general  discussion 
of  the  strength  of  columns.  The  following  is  given  as  supplementary  to  what  is  usually 
found  in  the  works  on  applied  mechanics,  and  on  framed  structures,  on  this  subject. 

\  "While  this  is  the  only  purely  theoretical  column  formula  which  is  true  in  practice, 

II  I  \ 

it  is  only  applicable  to  very  long  columns  ( -  >  150  for  pin  ends,  and   t  >  200  for  flat  ends  j , 

such  as  are  seldom  or  never  used  in  actual  structures,  and  hence  it  is  of  little  practical 
value.     This  form-da  must  never  be  used  for  the  ordinary  lengths. 


360 


THE  MATERIALS  OF  CONSTRUCTION. 

r  —  least  radius  of  gyration  of  the  cross-section  of  the  column,  in 
inches. 


a/    #.2  as    #4  tar  0s  #7  #0-  #3  /0 

FIG.  294.— Variation  of  Moduli  with  increasing  Percentage  of  Carbon  in  Steel.     (Wat. 

Ars.  Rep.,  1886.) 

In  Fig.  296  the  locus  of  this  equation  is  shown  for  E  •=•  30,000,000,  the 
coordinates  being  p  and  — . 

Theoretically,  for  a  perfect  column,  centrally  loaded,  the  strength  is  con- 
stant for  increasing  lengths,  this  strength  being  the  "  apparent  elastic  limit  " 
or  "yield-point"  of  the  material  (see  Fig.  294)  until  the  critical  length  is 
reached  under  ivhich  the  column  bends  indefinitely  under  its  maximum  load, 
when  for  any  further  increase  in  length  the  load  which  will  produce  this 
bending  regularly  diminishes  in  accordance  with  the  law  of  Eider's  curve. 

The  theoretical  locus,  therefore,  for  the  value  of  p  plotted  to  —  would  be  a 

horizontal  line  at  the  apparent  elastic  limit  of  the  material,  extended  to  an 
intersection  with  Euler's  curve,  and  then  down  along  this  curve  indefinitely. 
But  because  no  column  is  perfectly  straight,  nor,  perfectly  free  to  turn,  nor 


COMPRESSION  TESTS. 


361 


loaded  and  supported  exactly  in  its  gravity  axis,  nor  has  the  same  modulus 
of  elasticity  in  all  its  parts,  nor  is  of  exactly  uniform  cross-section,  etc.,  it 
follows  that  any  locus  derived  from  experiment  would  usually  fall  below  this 
theoretical  locus,  and  could  never  rise  above  it  except  from  a  higher  modulus 
of  elasticity,  or  from  a  higher  elastic  limit,  or  from  more  fixed  end  condi- 
tions than  had  been  assumed. 

In  making  tests  of  metal  columns  there  are  but  two  conditions  of  end 
supports  to  which  any  theory  can  be  adapted,  these  being  rigidly  fixed  in 
direction  and  absolutely  free  to  revolve.  As  it  is  impossible  to  satisfy  the 
former  condition,  the  latter  becomes  the  only  one  to  which  any  theoretical 
formula  should  be  expected  to  conform.  It  seems  remarkable,  therefore, 
that,  so  far  as  the  author  is  aware,  there  lias  been  but  one  set  of  observations 
made  which  has  fairly  satisfied  this  requirement,  these  having  been  made  by 
M.  Considere,  Ingenieur-en-chef  des  Fonts  et  Chaussees,*  France.  Both 
Prof.  Bauschinger  and  Prof.  Tetmajer  attempted  to  satisfy  this  condition, 
but  they  mounted  their  columns  with  cone  or  knife-edge  bearings  at  the 
computed  gravity  axes,  while  M.  Considere  mounted  his  with  lateral-screw 


O! 


B 


FIG.  295.— Considere 's  Mounting  for  Column  Tests.  (Fr.  Com.  Rep.,  vol.  in.  p.  124.) 
adjustments,  as  shown  in  Fig.  295,  and  arranged  a  very  delicate  electric 
contact  at  the  side  so  as  to  indicate  a  lateral  deflection  as  small  as  0.001  mm. 


*  First  reported  in  1889,  and  described  in  vol.  i.  p.  1*28  and  vol.  in.  p.  124  of  the 
Report  of  tJie  French  Commission  on  the  Methods  of  Testing  Engineering  Materials,  1895. 


362 


THE  MATERIALS  OF  CONSTRUCTION. 


He  then  applied  moderate  loads  to  the  columns  and  adjusted  the  end-bear- 
ings until  they  stood  under  such  loads  rigidly  vertical,  with  no  lateral  move- 
ment whatever.*  Then  with  his  double  knife-edge  bearings  at  each  end,  as 
shown  in  Fig.  295,  the  columns  were  perfectly  centred  and  absolutely  free 
to  move  or  turn  about  their  end  bearings,  as  the  theory  demands.  With 
these  conditions  perfected  he  made  155  tests  of  columns,  of  various  lengths 

from  —  =  40  to  —  =  3-40,  and  on  various  forms  of  cross-section. 


80M0 


FIG.  296  —One  Series  of  Results  of  M.  Considered  Column  Tests,  with  Material  having 
different  "  Apparent  Elastic  Limits."     (Rep.  Fr.  Com.,  vol.  in.  p.  124.) 

In  Fig.  296  the  author  of  this  work  has  plotted  the  tests  made  on  solid 
rectangular  steel  bars,  10  mm.  by  17  mm.  in  cross-section,  of  six  degrees  of 

*  This  precaution  is  essential  to  a  perfect  test  of  the  material  of  which  the  column  is 
composed.  Only  in  this  way  can  other  sources  of  weakness  be  eliminated.  It  is  to  the 
interest  of  the  contractor,  therefore,  to  provide  these  appliances. 


COMPRESSION  TESTS.  363 

hardness.  He  has  also  fitted  to  these  six  sets  of  observations  parabolic  loci 
which  cut  the  axis  of  loads  at  the  respective  "  apparent  elastic  limits,"  or 
"  yield-points,"  of  the  material,*  and  which  are  made  to  become  tangent  to 
Euler's  theoretical  curve  drawn  for  E  —  30,000,000.  The  close  agreement 
of  these  loci  with  their  respective  sets  of  observed  ultimate  strengths  would 
seem  to  indicate  that  they  cannot  well  be  improved  upon,  and  that  therefore 
this  parabolic  law  may  fairly  be  assumed  to  fit  the  actual  facts  in  an  ideal  set 
of  experiments  as  closely  as  it  is  possible  to  do.f 

It  further  appears  from  these  curves  that  the  coefficient  of  the  subtrac- 

/  IV 
tive  term  (-)    follows  a  very  definite  law,  as  shown  in  "  Modern  Framed 

Structures,"  p.  150.  Using  this  theoretical  value  of  this  coefficient,  we 
have,  as  the  maximum  strength  of  any  pivoted  wrought-iroii  or  steel  column, 
in  pounds  per  square  inch  for 


=  30,000,000,   ;- 


To  show  that  the  strength  of  a  column  is  no  function  of  the  ultimate 
strength  of  the  material  either  in  tension  or  compression,  M.  Considere  cold- 
rolled  the  medium  hard  steel  in  No.  5,  which  had  an  apparent  elastic  limit 
of  47,000  Ibs.  per  square  inch,  until  it  had  elongated  ten  per  cent  of  its 
original  length.  This  raised  its  elastic  limit  to  71,000  Ibs.  per  square  inch, 
while  its  ultimate  tensile  strength  was  raised  only  from  83,000  to  88,500  Ibs. 
per  square  inch.  Thus  metal  No.  0,  with  an  elastic  limit  of  71,000  Ibs.  and 
an  ultimate  strength  of  88,500  Ibs.  per  square  inch,  was  over  10  per  cent 
stronger  in  columns  than  metal  No.  8,  which  had  an  elastic  limit  of  64,000 
Ibs.  and  an  ultimate  strength  of  98,000  Ibs.  per  square  inch. 

While  the  parabolic  curves  hers  given  are  purely  empirical  in  form, 
theory  dictates  : 

1.  That  this  locus  shall  start  horizontally  from  the  vertical  axis  at  the 
"  apparent  elastic  limit  "; 

2.  That  it  shall  become  tangent  to  Euler's  curve;  and 

3.  That  it  shall  have  no  points  of  inflection  other  than  the  point  of  tan- 
gency  with  Euler's  curve. 

While  there  may  be  an  infinite  number  of  curves  which  would  satisfy 
these  requirements,  the  parabola  is  the  simplest  of  all,  and  it  also  seems  to  fit 
the  observations  as  well  as  any,  whether  these  observations  be  made  under 
ideal  conditions,  as  in  Fig.  296,  or  under  the  nearly  ideal  conditions  of  Prof. 
von  Tetmajer,  Figs.  297  and  298,  or  under  the  conditions  of  practice,  as  in 
Fig.  208  of  "  Modern  Framed  Structures." 


*  As  computed  from  the  ultimate  strengths  which  aloue  were  given  in  the  original 
communication,  the  yield-points  not  having  been  observed. 

f  The  author  had  already  developed  this  curve  as  best  representing -the  strength  of 
ordinary  columns  too  short  for  Euler's  formula  to  apply  to,  in  "  Modern  Framed  Struc- 
tures," p.  148  (1892). 


364 


THE  MATERIALS  OF  CONSTRUCTION. 


COMPRESSION  TESTS. 


365 


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366  THE  MATERIALS  OF  CONSTRUCTION. 

Prof,  von  Tetmajer's  tests  cover  a  great  variety  of  forms,  simple  and  com- 
posite, on  both  wrought-iron  and  steel,  and  the  results  of  these  tests  are  all 
plotted,  with  characteristic  symbols,  in  Figs.  297  and  298.  While  these 
results  scatter  somewhat,  owing  to  varying  elastic  limits  of  the  specimens  and 
to  the  fact  that  the  knife-edge  bearings  were  placed  at  the  computed  gravity 
axes,  and  were  not  adjusted  to  the  true  centres  by  lateral  adjustment  under 
small  loads,  as  were  those  of  M.  Considere,  still  the  parabolic  curve  fits  the 
average  position  of  the  plotted  points  as  well  as  could  be  desired.  See  also 
the  similar  diagram  for  wooden  columns  in  Chapter  XXXII. 

The  following  are  the  author's  parabolic  column  formulae  as  given  in 
"  Modern  Framed  Structures  " : 

ULTIMATE    STRENGTH    OF    COLUMNS,    IN    POUNDS    PER   SQUARE   INCH. 

For  Wrought-iron  Columns,  Pin  Ends,  ( -  <  170,1 

p  =  34,000  -  -67^-) (2) 

For  Wrought-iron  Columns,  Flat  Ends,  (  —  <  210,1 

p  =  34,000  -  .43  (j^) (3) 

For  Mild-steel  Columns,  Pin  Ends,  (-<  150,1 


=  42,000  -  .97         ......  .  .     .     (4) 


For  Mild-steel  Columns,  Flat  Ends,  (-  <  190,J 


p 


=  42,000  -  .62  (IV.     ...  (5) 


- 


For  Cast-iron  Columns,  Round  Ends,  (-  <  70  j 

p  =  60,000 (-)   .  (6) 

4-  \/*  I 

11  ~ 

For  Cast-iron  Columns,  Flat  Ends,    -^120, 

\r  i 


(?) 


COMPRESSION  TESTS.  367 

For  White-pine  Columns,  Flat  Ends,  (-  =  60, ) 

(8) 

For  Short-leaf  Yelloio-pine  Columns,  Flat  Ends,  \-j  <60,1 

p  =  3300 -.7  (t\ (9) 

For  Long-leaf  Yellow-pine  Columns,  Flat  Ends,  (-=  <60,J 

p  =  4000  -  .8  g)' (10) 

\U/  I 

For  White-oak  Columns,  Flat  Ends,  (y<60j 

p  =  3500  -  .8  (1)' (11) 

To  obtain  from  the  above  working  formulae  for  designing,  divide  both 
terms  of  the  right-hand  members  of  these  equations  by  the  factor  of  safety 
chosen  for  the  work  in  hand  and  for  the  material  used.  The  smallest  factors 
would  be  used  with  rolled  mild  steel,  and  the  largest  with  timber  and  cast 
iron. 

285.  Spring  Testing-machines. — Fig.  299  shows  a  form  of  spring  testing- 
machine  adapted  for  both  compression  and  tension  tests,  the  former  being 
made  at  A  and  the  latter  at  B.  It  is  made  in  two  sizes,  of  2500  and  4000 
Ibs.  capacity  respectively. 

In  Fig.  300  is  shown  a  spring  testing-machine  of  65,000  Ibs.  capacity, 
for  compression  only,  and  not  requiring  the  use  of  over- weights,  although 
such  are  furnished  for  one  half  the  total  load,  if  desired. 


368 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG.  299.— Spring  Testing-machine  for  both  Tension  and  Compression  Tests, 


Fiu.  800. — Spring  Testing-machine. 


CHAPTER  XVII. 
CROSS-BENDING  TESTS. 

286.  Objects  of  Cross-bending  Tests. — Brittle   materials  like  cast-iron, 
stone,  brick,  and  concrete  are  tested  in  cross-bending  to  determine  their 
ultimate  strength,  and  perhaps  also  their  resilience.    Timber  is  so  tested  also 
to  determine  its  ultimate  strength  and  its  modulus  of  elasticity.    Springs  and 
spring-steel  are  tested   in  this  way  to  obtain  their  elastic  limits  and  their 
deflections  under  given  loads,  and  railroad  rails  are   sometimes  tested  for 
elastic  limit  and  ultimate  strength.     Cross-bending  tests  are  also  made  for 
scientific  purposes  to  test  the  correctness  of  the  ordinary  formula  for  the 
strength  and  the  deflection  of  beams. 

Since  three  kinds  of  stress,  tension,  compression,  and  shearing,  are  devel- 
oped when  a  beam  is  bent  under  the  action  of  external  forces,  the  problem 
is  more  complex  than  those  considered  in  the  two  previous  chapters  Usually 
the  shearing  stresses  are  left  out  of  account  in  designing  both  for  strength 
and  stiffness,  but  the  conditions  under  which  this  stress  should  be  recognized 
and  taken  account  of  are  given  in  Article  38,  for  strength,  and  Article  46, 
for  deflection. 

287.  Essential  Considerations  in  Cross-bending  Tests. — The  essential  con- 
ditions which  must  be  satisfied  in  making  cross-bending  tests  are: 

1.  The  loads  should  be  applied  centrally  in  the  direction  of  the  greatest 
or  of  the  least  moment  of  inertia  of  the  beam,  in  order  to  prevent  torsion. 

2.  The   supports   must   be   rounded  knife-edges,  bearing   on  auxiliary 
plates  if  necessary  to  prevent  indentation. 

3.  The  loads  should  be  continuously  progressive,  without  shock,  and  in 
the  case  of  timber  they  must  increase  at  a  fixed  rate  with  no  stopping  when 
readings  are  taken. 

4.  The  deflections  must  be  measured  by  observing  the  movement  of  the 
neutral  plane  at  the  loaded  point  with   reference  to  the  neutral  pLine  at 
the  two  end  supports.     That  is  to  say,  the  deflection  apparatus  must  be 
attached  directly  to  the  specimen,  or  rest  on  the  end  bearings,  and  be  self- 
contained  with  the  test  specimen,  and  independent  of  all  deforming  move- 
ments of  the  machine  itself. 

The  fourth  condition  is  seldom  properly  satisfied.  It  is  common  to 
measure  deflections  with  reference  to  some  part  of  the  frame  of  the  testing- 

369 


370 


THE  MATERIALS  OF  CONSTRUCTION. 


machine,  assuming  this  to  be  rigid,  or  by  means  of  a  deflection  apparatus 
attached  to  this  framework  and  moving  with  it. 


FIG.  301. — The  Author's  Beam-testing  Machine. 

Cross-lending  Testing -machines. — In  the  author's  machine,  shown  in 
Fig.  301,  the  deflection  is  measured  by  means  of  a  micrometer-screw, 
reading  to  0.001,  inch  held  in  place  by  a  bar  which  is  attached  directly  to 
the  knife-edge  bearings  through  parts  which  are  not  under  stress.  The 
micrometer-screw  bears  upon  the  top  of  the  power  screw  which  presses 
on  the  centre  knife-edge.  As  all  these  bearings  have  steel  plates  intervening 
between  them  and  the  specimen  (if  this  be  timber),  the  movement  of  the 
centre  bearing,  with  reference  to  the  end  bearings,  is  registered  on  the 
micrometer-screw,  and  this  is  the  deflection  of  the  specimen.  One  half  the 
load  is  weighed  on  any  ordinary  form  of  platform-scales. 

In  the  large  beam-testing  machine  of  the  author's,  shown  in  Fig.  302, 
used  mostly  for  testing  large  wooden  beams,  the  deflection  is  measured  by 
means  of  a  fine  thread  attached  (at  one  end  by  a  rubber  band)  to  two  nails 
driven  into  the  stick  in  the  neutral  plane  over  the  end  supports.  At  the 
centre  a  nickel-plated  scale,  graduated  to  0.1  in.  and  polished  to  act  as  a 
mirror,  is  fastened  to  one  or  both  sides  of  the  beam.  The  thread  is  then 
read  on  this  scale  by  bringing  it  and  its  image  into  coincidence  and  esti- 
mating its  position  to  the  nearest  0.01  in.  The  load  is  applied  by  pumping 
oil  into  the  cylinder  below,  thus  depressing  the  screws  and  the  cross-head 
carried  by  them,  and  one  half  the  load  is  weighed  on  the  50,000-lb.  plat- 
form-scales under  one  end.  The  base  of  this  machine  consists  of  two  long- 
leaf  yellow-pine  sticks,  6x18  inches  in  section  and  24  feet  long,  with  a 
f  X  18-inch  steel  plate  inserted  between  them.  Its  capacity  is  100,000  Ibs. 

In  the  machine  shown  in  Fig.  303,  specially  designed  for  cast-iron  tests, 
the  deflection  is  correctly  indicated  on  the  graduated  arc  by  means  of  an 


CROSS-BENDING    TESTS. 


371 


372  THE  MATERIALS  OF  CONSTRUCTION. 

ingenious  arrangement  of  levers  underneath,  not  shown  in  the  figure.     Its 
capacity  is  4000  Ibs. 

In  Fig.  304  is  shown  Keep's  autographic  recording  transverse  test  appa- 


FIG    303. — Cross-bending  Testing-machine  for  Cast  Iron.     Deflection 

correctly  measured.  * 

i-atiis  for  his  standard  form  of  specimen  £  inch  square  by  12  inches  long. 
Ic  makes  an  autographic  record  like  those  shown  in  Chapter  XXIV,  the  de- 
flection of  the  test  specimen  being  taken  up  by  the  gradual  falling  of  the 
weighing-beam.  The  movement  of  the  poise  also  moves  the  paper,  while 
the  deflection  of  the  specimen  moves  the  pencil.  This  is  a  valuable  machine 
for  tests  on  this  size  of  specimen. 

The  universal  machines  shown  in  Figs.  256  to  260,  and  in  Figs.  266  and 
270,  are  all  adapted  to  making  transverse  tests  by  inserting  an  I  beam  or 
other  rigid  base  on  the  weighing-table  when  the  specimen  is  longer  than 
this,  and  supporting  the  specimen  on  it. 

288.  Importance  of  Measuring  the  Deflection  in  Transverse  Tests  of  Cast 
Iron. — The  importance  of  measuring  the  deflection  of  transverse-test  speci- 
mens of  cast  iron,  as  well  as  the  breaking  strength,  is  now  generally  recog- 
nized. The  resistance  of  the  metal  to  shock  is  measured  by  the  product  of 


CROSS-BENDING   TESTS. 


373 


the   ultimate    load    into   the   final   deflection,   divided    by  2,   this   being 

approximately  the    total    area    of    the    stress- 

diagram  in  cross-bending.     If  this  be  now  di- 

vided by  the  volume  of  the  metal  between  the 

end   bearings,   it   gives  resistance   to  shock  in 

inch-pounds  per  cubic  inch  of  metal.*     Since 

it  is  more  convenient,  however,  to  weigh  the 

bar  than  to  compute  its  volume,  the  resistance 

to  shock  is  commonly  computed  per  pound  of 

metal  (between  end  bearings). 

From  many  experiments  made  by  the  author, 
he  has  recommended  the  following  require- 
ments t  for  test-bars  about  1  inch  square: 

Inch-pounds  per         -c 
pound  of  Cast  Iron,     g 

For  the  lower  grades  of  castings  ....  20-30  \* 

For  good  machine  castings  .........  40-50  fc 

For   stove-castings,  and   for   impact  4 

machinery  ......................  60-70  £ 

In  this  way  both  the  strength  and  the  de-   Ef. 
flection    are    properly   allowed    for;   and  since  jj 
these   results  usually  vary  inversely  with   each  ~. 
other,  both   may  vary  greatly  without  showing  <? 
an  appreciable  variation   in   this   product,  and   p" 
hence  without  appreciably  changing  the  value  o 
of  the  metal.     On  the  other  hand,  the  strength   I 
may  be  very  high,  with  a  very  small  resistance  ~f 
to  shock;  that  is,  it  may  be  strong  in  a  static  -c 
test,  but  very  brittle.     These  products  will  be 
greater   for    small    (thin)   specimens   than   for 
thicker  ones;  so   the  only  safe  rule  is  to  find 
by   trial   what    products  can  be  expected   and 
demanded  for   any  given  product   and   size   of 
specimen. 

289.  The  Computed  Strength  in  Pounds  per 
Square  Inch  on  the  external  fibres  of  a  trans- 
verse-test specimen  is  found  from  the  formulas 
given  in  Art.  33.  Thus  for  any  form  of  section 
tested  to  failure  by  a  load  at  the  centre  the 
"modulus  of  rupture  "  in  cross-breaking  is 


*  It  was  shown  m  Arts.  53  to  57  that  the  resilience  was  always  proportional  to 
the  volume  of  the  body  subject  to  stress,  it  being  independent  of  the  dimensions  of  the 
body  so  long  as  the  form  of  cross-section  remained  the  same. 

f  See  a  paper  by  the  author  on  Gust  Iron,  Trans.  Am.  Soc.  C.  E.,  vol.  xxn.  p.  91. 


374  THE  MATERIALS  OF  CONSTRUCTION. 

/,  =  -!', (i) 

while  for  a  solid  rectangular  cross-section 

3  Wl 


and  for  any  form  of  cross-section  we  should  have 

f  --   Wly'  m 

/••-  -47- > W 

where  fr  —  modulus  of  rupture  in  pounds  per  square  inch; 
W=  breaking-load  at  centre  in  pounds; 
I  =  length  between  end  bearings  in  inches ; 
l>  =.  breadth  in  inches; 
Ji  =  height  in  inches; 
y}  =  distance  from  neutral  axis  to  outside  fibre  which  failed  under 

the  breaking-load,  in  inches; 

/  =  moment  of  inertia  of  the  cross-section  about  its  neutral  axis; 
M—  bending  moment  on  the  beam  at  the  section  of  rupture. 

Because  these  formulas  are  strictly  true  inside  the  elastic  limit,  it  must 
not  be  inferred  that  this  so-called  "  modulus  of  rupture  in  cross-bearing  " 
represents  any  actual  stress  on  any  outside  fibre,  either  in  tension  or  com- 
pression, ut  the  time  of  rupture.  (See  a  discussion  of  this  question  in  Arts. 
35  and  36,  p.  50.)  In  general  this  modulus  is  about  twice  the  tensile 
strength,  in  the  case  of  cast  iron,  while  in  timber  it  is  somewhat  below  an 
average  of  the  tensile  and  the  compressive  strength  of  the  wood.  With  this 
understanding  this  modulus  is  a  convenient,  though  conventional,  method 
of  stating  the  strength  of  any  material  under  cross-breaking  stress,  and  for 
comparative  purposes  it  is  very  useful.  For  the  purposes  of  the  designer, 
however,  these  formulas  are  strictly  correct,  since  he  always  works  with  loads 
and  stresses  inside  the  elastic  limits  of  the  materials  he  uses. 

290.  The  Modulus  of  Elasticity  (Stiffness)  is  preferably  found  from  a 
transverse  test,  since  it  is  mostly  used  for  computing  the  deflection  of  beams. 
Since  this  quantity  is  of  necessity  computed  from  loads  and  their  correspond- 
ing deflections  inside  the  elastic  limit,  it  follows  that  this  modulus  is  found 
to  be  practically  the  same  whether  it  is  computed  from  tensile,  compressive, 
or  transverse  tests.  Thus  Prof.  Tetmajer  tested  fourteen  rolled  wrought-iron 
I  beams,  from  4  to  16  inches  in  depth,  and  obtained  from  them  an  average 
value  of  E  =  27,840,000,  while  on  thirty-one  tension  tests  on  specimens  cut 
from  shape  iron  from  the  same  metal  he  obtained  a  value  of  E  =  28,110,000; 
ior  wrought-iron  riveted  plate  girders,  from  16  to  28  inches  deep,  he  ob- 
tained a  value  of  E  =  26,000,000. 
In  mild  steel  he  found 

For  the  tension  specimens     E  =  30,550,000; 
"     "  riveted  plate  girders  E  =  28,160,000. 


CHAPTER  XVIII. 

IMPACT  AND   HARDNESS  TESTS. 

MPACT   TESTS. 

291.  Object  of  Impact  Tests. — As  explained  in  Art.  53,  impact  tests 
cannot  give  absolute  results,  like  those  obtained  from  tension,  compression, 
and  transverse  tests,  and  hence  they  are  properly  used  only  where  other 
methods  of  testing  are  not  available.  They  are  commonly  employed  on  cast- 
iron  car-wheels,  on  cast-steel  and  malleable-iron  car-couplers,  and  on  car- 
axles  and  sometimes  on  rails  and  rail-joints.  Axles  and  rails,  however,  can 
be  tested  statically  in  cross-bending,  and  more  can  be  learned  by  testing  them 
in  this  manner,  by  bending  them  back  and  forth,  and  plotting  their  bending- 
stress  diagrams,  than  by  the  drop  tests.* 

Because  of  the  extreme  difficulty  of  arranging  an  impact  test  so  as  to  give 
to  the  specimen  a  plain  tensile  stress,  without  allowing  a  large  and  uncertain 
part  of  the  energy  of  the  blow  to  be  absorbed  in  the  auxiliary  appliances, 
this  has  seldom  been  attempted,  and  certainly  it  never  has  succeeded  in  giv- 
ing any  valuable  results. 

Impact  tests  in  compression  are  seldom  employed  except  to  produce  pene- 
tration of  a  standard  form,  to  determine  hardness,  which  will  be  described 
later  under  the  head  of  hardness  tests.  The  impact  test  given  to  car-couplers 
might  be  called  a  compression  test,  perhaps,  since  the  blow  is  given  "  end-on"  ; 
but  as  failure  here  occurs  by  breaking  off  portions  of  the  enlarged  head,  by 
developing  in  it  excessive  transverse  stresses,  it  is  really  a  transverse  test. 

In  general,  therefore,  impact  tests  are  all  transverse,  or  cross-bending, 
tests. 

The  author  has  also  introduced  a  species  of  impact  test  for  street-paving 
brick  in  place  of  the  abrasion  test  hitherto  employed.  This  was  done  from 
the  fact  that  paving-brick  do  not  wear  out  by  abrasion,  but  by  being  broken 
down  by  the  blows  from  horse's  shoes,  and  from  the  wheels  of  vehicles. 

*  Au  exception  may  have  to  be  made  in  the  matter  of  brittleness  of  metals  induced 
by  very  low  temperatures,  which  cau,  it  is  said,  only  be  determined  by  impact  or  drop 
tests. 

375 


376  THE  MATERIALS  OF  CONSTRUCTION. 

Impact  tests,  therefore,  are  usually  made  to  determine  the  resistance  te 
shock  of  structural  forms  which  cannot  readily  be  tested  in  any  other  way. 

292.  Essential  Conditions  of  Impact  Tests. — Since  the  force  of  a  blow 
depends  as  much  on  the  resistance  offered  by  the  body  struck  as  it  does  on 
the  striking  body,  it  follows  that  the  anvil,  or  bed,  of  an  impact  machine  is 
quite  as  important  as  the  weight  of  the  ram  and  the  height  of  its  fall.     A 
standard  impact   test,   therefore,  involves  a  standard  size  of  anvil  and  a 
standard  froundation  for  it,  quite  as  much  as  a  standard  weight  of  hammer 
and  standard  fall  of  same. 

The  pendulum  machine  would  seem  to  offer  one  advantage,  however, 
which  cannot  be  realized  in  drop  machines.  The  pendulum  machine  can  be 
so  designed  as  to  allow  the  pendulum  weight  to  pass  the  specimen  when  it 
breaks,  and  by  automatically  recording  its  extreme  movement,  and  deducting 
this  vertical  component  from  the  original  total  fall,  the  actual  energy  absorbed 
by  the  specimen,  up  to  rupture,  would  be  determined  proivded  the  anvil  is 
rigid.*  In  this  way  the  specimen  could  be  broken  on  the  first  blow,  and  the 
energy  spent  upon  it  (and  absorbed  by  it)  exactly  determined.  This  would 
seem  to  be  the  only  proper  way  to  make  comparable  impact  tests. 

The  Pennsylvania  Railroad  Company  has  standardized  the  impact  test 
of  cast-iron  car-wheels  and  of  car-axles,  and  the  American  National  Car- 
builders'  Association  has  now  (1896)  standardized  the  test  f  or  »car-axles  as 
indicated  in  Art.  29-t;  but  with  these  exceptions  it  can  hardly  be  said  that 
impact  tests  made  in  different  places  in  this  country  can  be  considered  as  at 
all  comparable,  because  of  a  want  of  identity  in  the  foundation  portion.  If 
the  impact  machine  be  of  the  pendulum  form,  it  must  strike  the  specimen 
at  the.  centre  of  percussion  of  the  entire  pendulum  in  order  to  prevent  a 
portion  of  the  energy  from  spending  itself  by  bending  the  pendulum. 
While  pendulum  machines  are  more  convenient,  drop  machines  are  more 
certain  to  deliver  the  full  theoretical  force  of  the  blow.  In  a  pendulum 
machine  the  energy  of  the  blow  is,  of  course,  the  total  weight  of  the  pendulum 
into  the  distance  through  which  its  centre  of  gravity  falls. 

293.  The  Energy  of  the  Blow. — The  unit  of  measure  in  impact  tests  is 
the  foot-pound  (or  kilogram-meter).     This  energy  cannot  be  measured  in 
pounds,  and  no  scheme  of  equivalents  can  be  devised  between  the  foot-pound 
units  of  an  impact  test  and  the  pound  units  of  a  static  test,  although  this  has 
often  been  attempted.     There  is  110  relation  between  the  resistance  to  shock 
and  the  resistance  to  a  static  load,  since  there  is  no  relation  between  the  total 
area  of  a  stress-diagram  and  its  stress  coordinate.     The  attempt  which  is 
often  made,  therefore,  to  equate  these  two  kinds  of  resistance  is  as  foolish  as 
the  ancient  practice  of  estimating  the  discharge  of  a  stream,  or  aqueduct,  or 
pipe  from  its  cross-section  alone. 

From  the  law  of  the  conservation  of  energy  we  have: 


*  Some  experiments  along  this  line  have  recently  been  made    by  Mr.  S.  B.   Russell, 
M.  Am.  Soc.  C.  E.,  in  the  St.  Louis  Water- works  Department. 


IMPACT  AND  HARDNESS  TESTS. 


377 


The  work  which  gravity  does  on  the  falling  weight,  and  which  is  wholly 
represented  by  the  energy  of  the  hammer  at  the  time  it  strikes, 
must  be  absorbed  by  the  resisting  body.  This  energy  is  equal,  in 
foot-pounds,  to  the  weight  of  the  ram  in  pounds  multiplied  by 
its  total  vertical  fall  (including  the  vertical  deflection  of  the 
specimen)  in  feet. 

In  the  case  of  a  pendulum  impact  machine  the  entire  weight 
of  the  swinging  parts  must  be  divided  into  two  parts,  and  these 
parts  concentrated  at  the  axis  of  rotation  and  at  the  centre  of 
percussion.  The  latter  part,  only,  multiplied  by  its  vertical 
drop  is  the  measure  of  the  energy  of  the  blow  (but  this  is  the 
same  as  the  total  weight  into  the  fall  of  its  centre  of  gravity). 

To  find  the  centre  of  percussion  and  the  equivalent  weight 
to  be  considered  as  concentrated  at  this  point,  a  graphical  solu- 
tion may  be  employed,  as  follows: 

Let  AG  extended,  Fig.  305,  be  the  pendulum,  with  its  axis 
of  rotation  at  A.  Let  G  be  the  centre  of  gravity  of  the  entire 
pendulum,  with  all  its  rigidly  connected  parts  (to  be  found  by 
trial).  -Let  GD,  drawn  perpendicular  to  AG  at  G,  be  made  (to 
the  given  scale)  equal  to  the  radius  of  gyration  of  the  entire 
pendulum  about  its  centre  of  gravity  G,  (to  be  computed). 

Then  draw  AD,  and  DC  perpendicular  to  AD,  cutting  AG 
extended  in  G.  Then  is  C  the  centre  of  percussion  of  the 
pendulum.*  If  the  graduated  arc  (see  Fig.  308)  have  a  radius  equal  to  AC, 
and  the  vertical  components  of  the  pendulum's  motion  (versed  sines)  be  laid 
off  on  this  arc,  then  the  equivalent  weight  to  be  concentrated  at  G  is  to  be 
used  for  computing  the  energy  of  the  blows,  and  this  equivalent  weight  is 


FIG.  805.  — 
Graphical 
Method  of 
Finding  the 
Centre  of 
Percussion. 


or  equivalent  weight  at 


Wc:  W::AG:AC', 


W.AG. 
-Hc-   ~ 


(1) 


where  TFis  the  total  weight  of  the  pendulum  used  in  finding  the  centre  of 
gravity  G. 

If  the  graduated  arc  has  a  radius  equal  to  AG,  then  the  total  weight  W 
is  to  be  used  with  the  versed  sine  to  compute  the  energy  of  the  blow. 

If  a  conventional  radius,  R,  has  been  used  by  the  maker  of  the  machine, 
then  a  corresponding  Wr  must  be  employed  which  will  satisfy  the  equation 


In  every  case,  however,  the  point  of  impact  of  the  pendulum  should  be 
at  C,  the  centre  of  percussion. 


Rankine's  Applied  Mechanics,  Art.  581. 


378 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG. 


-Most  Approved  Form  of  Impact-testing  Apparatus.      (Rep.  French   Com- 
mission. ) 


IMPACT  AND  HARDNESS  TESTS. 


379 


294.  Impact-testing"  Machines. — In  Fig.  306  is  shown  the  impact- 
machine  designed  and  used  by  Prof.  A.  Martens  in  his  testing  laboratory  at 
Charlottenburg,  Germany.*  Its  dimensions  are  given  in  meters.  It  admits 
of  an  extreme  fall  of  4.5  meters  (about  15  feet),  and  of  a  weight  of  ram  of 
200  kilograms  (440  Ibs.),  although  he  has  used  weights  of  36  and  56  kilograms 
only.  It  is  intended  for  specimen  tests  only.  The  anvil  weighs  1250  kilo- 
grams (2750  Ibs.),  or  22.5  times  the  heaviest  ram  usually  employed.  This  in 
turn  is  set  on  a  strong  cement-masonry  foundation,  separate  from  that  of  the 
building, f  as  should  always  be  done  with  drop  machines. 

The  National  Car-builders'  Association  of  America  has  (1896)  adopted  a 
spring  support  to  the  anvil,  as  shown  in  Fig.  307,  in  order  to  insure  perfect 


FIG.  307.— Standard  Impact-testing  Machine  with  the  Anvil-block  on  Springs,  as 
recommended  by  the  Master  Car-builders  of  America,  1896.  Previously  used  by 
the  Penn.  Ry.  Co. 

identity  of  reactions  in  different  machines.     This  is  perhaps  the  only  way  to 
eliminate  the  varying  effects  of  different  foundations  of  the  anvil-block. 
Fig.  308  gives  a  view  of  Keep's  autographic  recording  pendulum  impact- 

*  See  Mittheilungen  am  den  Koniglichen   Tcchnischen   Versuchsanstalten  zu  Berlin, 
1891,  p.  2,  and  Plate  I.     The  machine  was  made  by  E.  Becker,  machinist,  Berlin. 

f  At  first  it  was  set  on  the  floor,  but  it  was  found  necessary  to  put  it  on  a  more  solid 
foundation. 


380 


THE  MATERIALS  OF  CONSTRUCTION. 


machine.     It  is  used  only  for  testing  his   standard  cast-iron  bars  $  inch 
square  and  12  inches  long.     The  hammer  weighs  25  Ibs.,  and  swings  on  a 


FIG.  308.— Keep's  Impact- testing  Machine. 


IMPACT  AND  HARDNESS  TESTS. 


381 


radius  of  6  feet.  The  weight  of  the  anvil  is  admitted  to  be  too  light,  and 
the  designer  recommends  that  it  be  set  against  a  brick  wall !  *  The  d,rc  is 
graduated  to  vertical  drops  of  J  inch,  with  a  total  fall  of  6  inches.  The 
paper  on  which  the  deflection  is  recorded  at  each  blow  is  automatically 
moved  T3g-  inch  after  each  blow,  so  that  the  record  consists  of  a  series  of 
parallel  lines,  each  being  the  deflection  for  that  blow,  magnified  four  or  five 
times  by  the  leverage  of  the  recording  apparatus. 

TESTS   FOR   HARDNESS. 

295.  Hardness  Defined. — The  term  hardness  is  used  in  two  senses,  as 
applied  to  metals,  minerals,  and  other  solids.     It  is  used  to  signify— 

(a)  Resistance  to  indentation  (permanency  of  form) ; 

(b)  Resistance  to  abrasion  or  scratching  (permanency  of  substance). f 
These  two  kinds  of  hardness  are  more  or  less  related,  and  are  often  con- 
fused.    In  practice  the  demands  for  these  two  kinds  of  hardness  are  quite 
distinct,  and  hence  two  very  distinct  kinds  of  tests  are  employed  to  determine 
them. 

296.  Hardness  Test  for  Permanency  of  Form  or  Resistance  to  Indenta- 
tion.— The  only  test  of  this  kind  which  has  ever  been  standardized  is  the 
indentation  test  by  means  of  a  pyramidal  steel  punch,  attached  to  a  falling 


FIG.  309. — The  Rodman  Steel  Punch  for  Hardness  Tests.     Dimensions  in  millimeters. 
(Rep.  Fr.  Com.^  vol.  in.  p.  261.) 

weight.  The  form  most  favorable  to  exact  results  is  that  chosen  by  Lieut. - 
Col.  T.  J.  Rodman  (IT.  S.  A.)  before  18GO,J;  and  shown  in  Fig.  309  in 
metric  measurements.  These  are  used  because  this  test  has  been  standard- 
ized in  France,  and  the  degree  of  hardness  is  given  in  metric  units. §  Such 
a  steel  point  is  rigidly  attached  to  the  base  (or  striking  side)  of  the  ram  in  an 
impact-testing  machine,  such  as  shown  in  Fig.  300  or  307  or  308.  The  sur- 

*  Evidently  the  particular  character  of  this  setting  will  greatly  affect  tho  force  of  the 
blow  on  the  specimen. 

f  After  Osmond. 

%  See  his  Report  of  Experiments  on  Metals  for  Cannon  and  Cannon-powder,  1861. 

§  While  the  author  of  this  work  has,  as  a  rule,  expressed  quantities  in  English  units 
only,  he  makes  an  exception  in  this  case. 


382  THE  MATERIALS  OF  CONSTRUCTION. 

face  of  the  substance  to  be  tested  is  planed  or  filed  flat  and  polished.  The 
steel  point  is  then  made  to  fall  normally  upon  the  surface  from  any  desired 
height,  and  the  observation  consists  in  noting 

The  weight  of  the  ram  =  irin  kilograms; 

The  height  of  the  fall  =  h  in  millimeters; 

The  length  of  the  indentation  =  /  in  millimeters. 

The  work  done  upon  the  body  tested,  or  in  producing  the  indentation,  will 
be  Wli  kilogram-millimeters,  provided  the  anvil,  or  body  struck,  was  very 
massive  and  firm  in  comparison  with  the  weight  of  the  ram.  This  is,  of 
course,  essential  to  the  correctness  of  the  assumption  that  the  energy  of  the 
falling  body  spends  itself  wholly  in  producing  the  indentation;  and  this  must 
be  assumed  and  secured  for  a  perfect  accordance  of  results. 

The  volume  of  displaced  material  resulting  from  the  indentation  will  be 
ml2,  where  m  will  vary  with  different  forms  of  pyramids,  but  will  be  a  con- 
stant for  any  one  pyramid,  or  punch.  It  has  been  shown  most  conclusively 
by  Lieut. -Col.  Martel  *  that  when  the  essential  conditions  of  the  test  are 
satisfied, 

For  all  forms  of  pyramids,  for  all  weights  of  ram,  and  for  all  heights  of 
fall,  the  volume  of  the  displaced  material  of  a  given  quality  is  equal  to  the 
energy  of  the  blow  (Wh)  divided  by  a  constant,  D,\  which  constant  is  the 
work  or  energy  necessary  to  displace  (by  deformation]  a  unit-volume  of  that 
material.  This  constant  is  therefore  characteristic  of  that  material  and  may 
be  taken  as  its  index  of  hardness,  or  of  its  resistance  to  indentation. 

Since  the  kilogram-millimeter  anits  have  already  been  used  in  France, 
and  the  hardness  of  many  kinds  of  materials  has  been  found  and  published 
011  this  scale,  it  would  lead  to  unnecessary  confusion  to  change  the  units, 
since  this  would  change  the  numerical  index  of  hardness. 

To  find  the  volume  of  the  pyramidal  displacement  of  the  Rodman  punch 
(Fig.  309)  from  the  measured  length,  multiply  the  cube  of  the  length  by 
0.0009413  (log  1.97375),  or  vol.  =  0.0009413Z3. 

For  any  other -form  of  punch  the  volume  would  be  readily  computed,  but 
approximately  this  form  is  best,  because  it  gives  u  very  large  length  to  be 
measured  for  a  very  small  volume.  In  other  words,  we  argue  from  a  longer 
base,  thus  making  the  percentage  error  of .  observation  correspondingly  less. 
Furthermore,  the  indentation  is  shallow  and  hence  injures  the  material 
(which  may  be  a  finished  or  unfinished  final  form)  to  a  less  degree.  Any 
other  form  would,  however,  give  strictly  comparable  results,  so  that  there  is 
no  real  necessity  of  adopting  this  particular  form.  It  goes  without  saying 
that  the  punch  should  itself  be  so  hard  as  not  to  suffer  any  permanent  de- 
formation in  service. 

The  truth  of  the  theory  that  V  =  — -r—  has  been  established  by  Martel 

*  Commission  des  Methodes  d'Essai  des  Materiaux  de  Construction,  vol.  in.  p.  261. 
f  For  durete,  hardness. 


IMPACT  AND  HARDNESS  TESTS.  383 

within  the  limits  of  the  errors  of  observation,  and  hence  can  be  accepted 
with  confidence,  as  giving  an  absolute  standard  by  which  to  measure  hard- 
ness when  this  implies  resistance  to  indentation.  The  following  table  con- 
tains values  of  D  (degrees  of  hardness  On  the  Martel  scale)  in  kilogram- 
millimeter  units  for  various  metals. 

DEGREES   OF   HARDXESS   OX   THE   MARTEL   SCALE. 

Metals  Tested.  De-ree  of   Hardness. 

Kilogram-millimeter  Units.* 

High  carbon  ("  diamond'')  steel,  hardened  in  oil. .          613 

"          "  "  "      not  hardened 460 

Medium  steel  (for  cannons),  hardened  in  oil 455  to  300 

Hoop-steel  (for  large  guns),  hardened  in  water 330  to  295 

Rolled  wrought  iron 226 

Hammered  wrought  iron 238 

Cast  iron  (for  guns) 300  to  208 

Bronze  (cast  in  shells) 154 

"       after  cold-hammering 238 

"       after  drawing  down  12$  on  a  mandrel 310 

"       cast  in  sand  (C  88,  Sn  12,  Z  2) 137 

"          "     "     "     without  zinc. . 115 

Copper,  rolled    . , 156 

"         reheated  and  cooled  in  water. .  , 64 

Zinc,  rolled 77 

Tin,  cast 33 

Lead,  cast , . . .  9 

297.  Hardness  Test  for  Permanency  of  Substance  or  Resistance  to  Abra- 
sion.— While  a  great  many  tests  of  this  property  have  been  devised  and  used, 
none  of  them  has  given  such  satisfactory  measurable  results  as  the  one  just 
described  for  resistance  to  induction.  The  scratch  test  has  long  been  in  use 
for  classifying  minerals  as  to  their  hardness,  and  ten  grades  of  hardness  are 
recognized  under  this  test.  It  is  purely  relative,  and  is  entirely  inadequate 
to  the  requirements  of  the  user  of  metals.  By  this  test  the  body  A  is  harder 
than  1>  when  a  point  or  sharp  corner  or  edge  of  A  will  scratch  the  surface 
of  13,  and  when  the  converse  will  not  hold. 

Mr.  Thomas  Turner  has  devised  the  instrument  shown  in  Fig.  310,  and 
this  has  been  largely  used  by  both  Turner  and  W.  J.  Keep  for  the  grading 
of  cast  irons  for  hardness.  In  this  a  diamond  point  is  fixed  at  the  base  of 
a  vertical  pencil  which  is  carried  by  a  perfectly  balanced  arm.  Provision  is 
made  for  loading  the  pencil  by  weights  (in  grams),  and  the  hardness  is 
indicated  by  the  number  of  grams  required  to  make  a  standard  scratch  on 
the  surface  tested.  Evidently  the  standardizing  of  the  scratch  offers  great 


To  change  these  figures  to  pound-inch  units,  multiply  by  1422. 


384 


THE  MATERIALS  OF  CONSTRUCTION. 


difficulties,  so  that  results  obtained  by  this  instrument  in  the  hands  of 
different  persons  would  probably  not  be  strictly  comparable. 

Prof.  Martens  (Berlin)  has  undertaken  to  standardize  this  instrument  by 
making  the  load  on  the  pencil  a  constant  and  measuring  the  width  of  the 


FIG.  310. — Turner's  Apparatus  for  Testing  Hardness. 

scratch  with  a  micrometer-microscope,  and  this  is  the  method  employed  by 
the  German  artillery  officers. 

Standard  abrasion-machines  have  also  been  used  (see  Fig.  288),  but  it  is 
almost  impossible  to  duplicate  the  conditions  exactly. 

In  general,  therefore,  it  may  be  said  that  there  is  now  no  absolute  test 
for  hardness  as  meaning  resistance  to  scratching  or  abrasion.  (For  a  brief 
account,  without  illustrations,  by  Osmond,  of  the  many  devices  which  have 
been  tried,  see  Report  of  the  French  Commission)  vol.  in.  p.  279.) 


CHAPTER  XIX. 

SHEARING  AND  TORSION  TESTS. 
SHEARING   TESTS. 

298.  Essential  Conditions  of  a  Shearing  Test. — In  order  to  obtain  the 
true  shearing  strength  of  any  substance  it  is  necessary  to  develop  in  it,  along 
a  given  plane,  shearing  stress  only,  unaccompanied  by  the  bending  stresses  of 
tension  and  compression.     To  accomplish  this  it  is  necessary  to  concentrate 
the  external  forces  of  action  and  reaction  on  planes  an  infinitely  small  dis- 
tance (dx)  apart.     Any  finite  distance  between  these  planes  will  develop  a 
cross-bending   action  and  its  resultant  direct  stresses  across  the  plane  of 
shear.     As  it  is  impossible  to  so  concentrate  the  external  shearing  forces,  it 
is  necessary  to  overcome  the  bending  stresses  set  up  by  the  non-concurrence 
of  the  external  forces  by  preventing  the  bending  of  the  specimen  subjected 
to  these  forces.     This  can  only  be  done  by  reinforcing  the  specimen  between 
the  shearing  planes.     This  may  be  done   by  grooving  the  specimen  in  the 
planes  of  shear,   or  by  supporting  it  by  auxiliary  clamps.     As  neither  of 
these  expedients  has  usually  been  resorted  to  in  shearing  tests,  it  follows 
that  very  few  such,  tests  have  ever  been  made  in  which  shearing  stress  has 
been  unaccompanied  by  large  direct  stresses.* 

299.  The  Occurrence  of  Shearing  Stress  in  Practice. — Shearing  stress  is 
present  in  nearly  all  cases  where  there  is  cross-bending  (see  Art.  37),  and  in 
rivets,  bolts,  bridge-pins,  crank-pins,  etc.,  shearing  stress  becomes  of  practi- 
cal interest.     In  none  of  these  cases,  however,  is  it  found  acting  alone,  but 
it  is  always  combined  with  bending  stress.     In  the  case  of  rivets  it  is  always 
combined  with  a  very  great  tensile  stress,  caused  by  the  contraction  of  the 
rivet  in  cooling  after  the  heads  have  been  made,  this  stress  from  contraction 
in  good  work  always  exceeding  the  tensile  stress  of  the  rivet  at  its  elastic 
limit.     In  fact  a  riveted  joint,  if  well  made,  always  acts  by  frictional  re- 
sistance alone,  since  this  is  always  more  than  the  working  stress  on  the  joint. 
(See  a  discussion  of  this  subject  in  Chap.  XXVI.)    While  rivets  are  computed 
for  shear,  therefore,  as  a  matter  of  fact  they  are  seldon  subjected  to  a  shear- 
ing stress. 

*  Both  Dr.  Kennedy  and  Mr.  Barba  grooved  their  specimens  for  double  shear,  and 
also  held  them  in  rigid  forms.     See  Rep.  French  Commission,  vol.  m,  Plate  XIX. 

385 


386 


THE  MATERIALS  OF  CONSTRUCTION. 


For  these  reasons  a  knowledge  of  the  true  shearing  strength  of  any  of 
the  metals  is  of  little  value,  except  for  purely  scientific  purposes,  and  for 
computing  resistance  to  torsion,  where  the  stress  developed  is  that  of  pure 
shear. 

In  the  case  of  timber,  however,  which  more  often  fails  in  shearing  along 
the  grain  than  in  any  other  way,  the  strength  in  shearing  is  of  great  interest. 

In  general  the  shearing  strength  of  the  metals  may  be  taken  as  80  per 
cent  of  the  tensile  strength. 

300.  Shearing-test  Appliances. — Shearing  tests  can  be  made  in  an  ordi- 
nary tension  or  compression  machine,  if  suitable  appliances  be  used  for 
holding  the  specimen.  In  Fig.  31 1  Dr.  Kennedy's  appliances  for  single  and 


FIG.  311.— Dr.  Kennedy's  Appliances  for  Single  and  for  Double  Shear. 

double  shear  are  shown.  For  single  shear  the  specimen  is  held  by  two  half- 
rounds,  all  enclosed  in  a  cylindrical  sleeve.  The  shearing-faces  are  rein- 
forced by  steel  rings.  The  plane  of  shear  thus  lies-  in  the  line  of  the  axes 
of  the  two  compression  shear-blocks.  For  double  shear  the  specimen  is 
grooved  on  the  shearing-planes,  and  it  is  also  fitted  closely  into  the  eyes  of 
the  steel  links  through  which  the  forces  are  applied.* 

In  Fig.  312  is  shown  the  shearing-apparatus  designed  by  the  author 
for  finding  the  shearing  strength  of  cast  iron.  Here  the  specimen  is 
gripped  firmly  at  both  ends  and  in  the  centre,  and  all  bending  distortion 
prevented.  By  preventing  this  kind  of  deformation  the  bending  stresses  are 
of  necessity  avoided.  The  bearing  shear-plates  at  top  and  bottom  are  of 
hardened  steel. 

For  shearing  tests  on  wood  the  apparatus  shown  in  Fig.  313  has  been 
extensively  employed  by  the  author.  Blocks  about  2£  inches  square  and  8 
inches  long  are  slotted  one  inch  from  each  end,  in  planes  at  right  angles  to 
each  other,  and  also  bored  at  the  centre  for  the  fixed  hold.  A  rectangular 
steel  pin  is  inserted  in  the  slot,  and  the  stick  is  prevented  from  splitting  by 
attaching  a  clamp  with  an  initial  pressure  just  sufficient  to  hold  it  in  place. 
The  steel  pin  is  pulled  by  means  of  bronze  stirrups  which  are  held  in  the 

*  This  apparatus  will  not  serve  for  cast  iron.  See  Trans.  Inst.  Civ.  Enyrs.,  vol.  xc. 
p.  391. 


SHEARING   AND   TORSION  TESTS.  387 

regular  wedge-grips  of  the  testing-machine.  After  shearing  out  one  end  of 
the  specimen  it  is  turned  over,  the  lower  stirrup  revolved  90°,  and  the  other 
end  pulled. 


FIG.  312. — The  Author's  Shearing-test  Apparatus. 
TORSION  TESTS. 

301.  Contrasted  with  Shearing  Tests. — While  torsional  stress  is  a  purs 
shearing  stress   (and   about  the  only  means  of  obtaining  a  pure  shearing" 
stress),  yet  a  torsion  test  differs  from  a  shearing  test  in  that  the  deformation, 
acts  over  any  length  of  bar,  taken  at  pleasure,  and  in  that  it  is  not  uniformly 
distributed  across  the  section,  but  is  zero  at  the  centre  and  increases  uni- 
formly towards  the  circumference.     This  enables  the  modulus  of  shearing 
elasticity  to  be  determined  by  noting  the  angular  distortion  over  a  given 
length  of  bar,  and  it  also  makes  possible  the  obtaining  of  autographic  (or 
plotted)  stress-diagrams  for  shearing  stress.     The  elastic  limit  and  ultimate 
strength  in  torsion  have  a  value  in  the  designing  of  shafting  of  all  sorts 
which  serve  to  transmit  power. 

302.  Torsion-testing  Machines. — in  Fig.  314  is  shown  a  simple  attach- 
ment to  an  ordinary  "  universal '  testing-machine.    The  power  is  applied  to> 
the  specimen  A  by  the  screw-gear  //,  and  the  torsion  is  resisted  by  a  couple> 


388 


THE  MATERIALS  OF  CONSTRUCTION. 


Shearing 

Test 
Apparatus 

for 
Wood. 


4mrm 


FIG.  313. — Sliearing-tLSt  Apparatus  for  Wood. 


SHEARING  AND   TORSION  TESTS. 


389 


FIG.  314. — Torsion-test  Attachment. 


FIG.  315.— Torsion  Machine  for  Short  Specimens. 


390 


THE  MATERIALS  OF  CONSTRUCTION. 


one  arm  of  which,  G,  bears  on  the  weighing-table.  The  angular  deforma- 
tion is  observed  by  means  of  the  two  collars  E  and  D,  the  latter  holding 
rigidly  a  bar  which  moves  a  pointer  over  the  graduated  circle  on  the  former. 


In  Fig.  315  is  shown  a  torsion  machine  for  testing  large  specimens  in 
short  lengths,  while  in  Fig  316  is  shown  a  large  machine  for  bars  of  any 
desired  length.  The  former  machine  is  self-contained,  while  in  the  latter 


SHEARING   AND   TORSION  TESTS. 


FTG.  317-— A  3|-iu.  square  Bessemer-steel   Bar  Twisted  Hot.     (Cassicr's  Mag.,  vol.  x.  p. 

44,3,  1896.) 


392 


THE  MATERIALS  OF  CONSTRUCTION. 


the  lifting  side  of  the  weighing  end  is  held  down  to  the  track  by  bolts,  and 
the  downward-bearing  end  of  the  conple-arm  bears  upon  a  system  of  weigh- 


FIG.  318. — Tet major's  Torsion-testing  Machine  for  Wires,  giving  Autographic  Records, 

ing-levers,  it  is  made  in  three  sizes  suited  to  steel  shafts  1£  in.,  2  in.,  and 
3-J  in.  in  diameter,  and  for  16  feet  in  length  or  less.  In  this  machine  the 
specimen  is  free  to  contract  longitudinally  while  under  test. 


FIG.  319. 

A  very  perfect  machine  for  testing  wires  from  0.05  in.  to  0.18  in.  in 
diameter  (No.  18  to  No.  7  13.  W.  G.)  and  for  giving  (a)  the  breaking  moment, 
(b)  the  number  of  turns,  and  (c)  the  complete  stress-diagram,  is  shown  in 
Fig.  318.*  This  machine  is  used  by  Prof.  Tetmajer  and  described  by  him 

*  Made  by  Messrs.  Amsler-Laffoii  &  Sous,  Schafl'hausen,  Switzerland 


SHEARING  AND    TORSION  TESTS.  393 

in  vol.  iv.  of  his  Communications.  The  specimen  is  kept  in  tension 
during  the  test  by  a  weight  suspended  by  a  cord  connected  to  the  carriage 
at  the  resisting  (and  recording)  end  of  the  specimen.  The  resisting  moment 
is  developed  by  means  of  two  weights  suspended  by  cords  which  run  in 
symmetrically  arranged  spiral  grooves. 

A  simple  machine  without  recording  apparatus  is  shown  in  Fig.  319. 


CHAPTER  XX. 


COLD-BENDING  AND  DRIFTING  TESTS. 
COLD-BENDING  TESTS. 

303.  Their  Character  and  Significance.— The  test  of  the  ductility  of  a 
malleable  metal  by  bending  it  cold  is  the  most  common  and  perhaps  the  most 
useful  of  all  the  tests  which  can  be  applied  to  it.  For  wrought  iron  and 
structural  steel  this  test  approaches  more  nearly  to  the  severe  usages  of  actual 
practice  than  does  the  tension  test  with  its  elastic  limit,  ultimate  strength, 
elongation,  and  reduction  of  area.  It  is  not  so  easily  standardized,  however, 
and  it  is  employed  less  in  America  than  in  Europe,  partly  because  no  stand- 
ard methods  and  results  have  been  agreed  upon  here.  If  a  sample  of  wrought 
iron  or  steel  will,  when  cold,  fold  upon  itself  absolutely,  as  shown  in  Figs. 


Thickness  of 


FIG.   320.— Cold-bending  Test   of    a  51-lb.    15-iu.    Steel   Channel-bar, 
web  =  0.78  in.     (Engr.  News,  vol.  xxxm.  p.  212.) 

320  and  322,  or  make  the  double  fold  as  shown  in  Fig.  321,  there  can  be 
no  doubt  of  its  high  quality.  When  it  fractures,  however,  at  intermediate 
stages  of  this  process,  the  question  of  its  quality  is  left  in  doubt,  and  some 
standard  limit  is  required  if  this  test  is  to  be  made  the  basis  of  acceptance. 
The  great  advantage  of  this  test  is  that  it  can  be  made  at  any  time  in  the 
shop,  without  the  expense  attaching  to  tension  tests,  and  by  the  man  who 
uses  or  makes  up  the  material.  No  standard  method  of  making  this  test, 
therefore,  should  remove  it  beyond  the  range  of  ordinary  shop  appliances. 
In  Europe  a  number  of  special  machines  are  in  use  for  making  these  tests, 

394 


COLD-BENDING   AND  DRIFTING   TESTS. 


395 


but  only  siiop-tools  will  here  be  assumed  as  available.  With  these  methods, 
and  in  the  hands  of  the  same  operator,  uniform  and  comparable  results  may- 
be obtained. 

304.  Methods  of  Making  Cold-bending  Tests. — If  the  specimen  is  not 
too  large,  a  strong  vise  may  be  employed.  If  the  bend  is  to  be  a  true  fold 
(radius  of  curvature  =  0),  the  specimen  should  be  bent  about  the  sharp  edge 
of  the  vise.  If  it  is  to  be  bent  to  a  given  radius,  an  auxiliary  plate,  dressed 
to  this  radius,  mast  be  clamped  with  the  specimen  in  the  vise.  In  either 


FIG.  321. — Double  Cold  licuds  on  f-iu.  Su-el  Plates.     (Eng.  News,  vol.  xxxin.  p.  272.) 

case  the  specimen  must  be  damped  fast  to  a  long  steel  bar,  or  lever,  so  as  to> 
prevent  all  bending  beyond  the  curved  section.  For  this  purpose  two  clamps :lc 
are  required,  one  of  which  must  be  close  down  to  the  vise.*  The  specimen, 
is  then  bent  to  90°  by  hand.  Striking  the  specimen  with  a  hammer  should, 
be  avoided,  as  this  kind  of  action  cannot  be  standardized.  If  the  specimen 
is  to  be  folded  flat  upon  itself,  it  may  be  removed  from  the  vise  after  it  has'- 
been  bent  to  a  right  angle,  and  a  second  bar  clamped  to  the  other  leg,  and 
these  two  bars  can  now  be  drawn  together  by  hand.  The  final  closing  down 
of  the  specimen  may  be  done  in  a  vise  or  under  the  hammer, — a  steam- 
hammer  always  preferred. 

The  French  Commission  have  adopted  the  interior  angle  as  the  index  of 
the  ductility.  Thus  if  a  straight  bar  bends  through  an  angle  of  GO0  before 
rupture,  it  leaves  an  angle  of  120°,  and  this  is  the  angle  of  record.  A  record 
of  0°  signifies  that  the  bar  has  bent  through  180°,  and  that  it  has  been 
either  closed  down  Hat  or  bent  to  a  given  radius,  according  as  the  radius  of 
the  bend  is  given  as  zero  or  something  greater. 

*  Specially  devised  stirrups  or  clevises  should  be  made  up  for  clamping  the  specimen- 
to  the  bending  bar. 


396 


THE  MATERIALS  OF  CONSTRUCTION. 


If  the  specimen  is  too  large  to  bend  by  hand  as  described  above,  it  may 
be  bent  under  a  steam- hammer  (or  in  a  hydraulic  or  screw  press,  or  in  a  test- 
ing-machine, or  even  by  a  heavy  sledge),  by  resting  it  on  supports  as  a 
be-im  and  striking  it  at  the  centre.  After  bending  it  in  this  way  through  an 


.• 


. 


FIG.  322. — Soft  Bessemer-steel  Bars,  3  in.  by  2  in.  in  cross-section,  Bent  Cold.    (Cassier's 

Mag.,  vol.  x.  p.  442,  1896.) 

angle  of  about  60°,  it  may  be  set  on  end  and  struck  by  the  hammer  (or  placed 
in  a  press  or  testing-machine),  as  a  bent  column,  and  so  brought  down  to 
any  desired  angle  or  radius  of  curvature.  This  required  radius  of  curvature 
will  ha.ye  to  be  reached  by  flattening  down  the  bent  bar,  nfter  the  zero  angle 


COLD-BENDING  AND  DRIFTING    TESTS. 


39T 


(180°  of  curvature)  has  been  attained.  The  ideal  appliance  here  is  a  press 
of  some  sort,  but  this  requires  a  special  machine  (perhaps  an  ordinary  "  bull- 
dozer," used  for  straightening,  or  curving  members,  might  serve),  and  in  the 
absence  of  these  a  steam-hammer  answers  very  well.  A  sledge  is  not  good, 
as  it  is  too  light  and  requires  blows  having  too  high  a  velocity,  which  spend 
their  energy  in  deforming  the  specimen  at  the  point  of  impact  and  may 
produce  its  rupture  earlier  than  the  other  methods  would. 

Prof.  Tetmajer  has  a  machine  for  making  bending  tests  without  the  use1 
of  a  mandrel,  and  whereby  a  uniform  bending  action  is  given  to  the  bar. 
This  develops  the  distributed  elongation  of  the  specimen,  whereas  a  bend, 
concentrated  at  one  point  develops  the  "  reduction  of  area  "  quality.  Thus 
a  high-grade  steel  wire  which  will  not  elongate  over  two  or  three  per  cent 
may,  on  failure  in  tension,  show  a  reduction  of  area  of  GO  per  cent.  Such 
a  wire  would  fold  over  to  a  much  sharper  curve  (smaller  radius)  than  it 
could  be  bent  to  through  a  full  circle. 

Preparation  of  the  Specimen. — If  the  specimen  has  been  cut  from  a- 
plate  or  from  a  structural  form,  and  it  is  to  be  tested  in  comparison  with  or 
on  the  same  basis  as  rolled  bars,  either  round  or  rectangular,  then  the 
sheared  edges  should  be  removed  by  planing  or  filing  where  the  bending  is 
to  be  effected,  in  order  to  remove  the  brittle  material  resulting  from  the 
shearing  action. 

On  the  other  hand,  if  it  is  desired  to  learn  the  action  of  the  metal  after 
it  has  been  punched  or  sheared  or  threaded,  then  the  specimen  is  purposely 
so  prepared  and  tested  without  removing  these  hardened  and  serrated  sur- 
faces. The  cold-bending  test  of  such  prepared  specimens  develops  the 
injurious  effects  of  these  shop  processes  (punching,  shearing,  and  threading) 
as  nothing  else  can,  and  it  is  therefore  necessary  to  use  it  for  such  purposes. 

The  French  Commission  have  recommended  a  length  of  10  inches  and  a, 
width  (of  plate  specimens)  of  1.6  inches,  the  thickness  to  be  that  of  the  plate 
or  bar. 

Sometimes  specimens  are  nicked  or  grooved  on  one  side  and  then  broken 
in  cross-bending,  under  the  hammer,  to  test  relative  brittleness.  This  is- 
not  a  test  that  can  be  relied  on  to  give,  absolute  results,  but  Prof.  Tetmajer 
used  it  to  good  effect  to  disprove  the  commonly  accepted  theory  that  even 
low  steel  is  more  brittle  than  wrought  iron  when  subjected  to  shocks- 
Photographic  views  of  the  results  of  these  tests  are  shown  in  Fig.  323.  The- 
depths  of  these  specimens  are  shown  in  the  figure.  The  six  upper  ones  were 
0.8  inch  thick,  and  the  four  lower  ones  1.2  inches  thick.  The  tension  tests- 
on  these  specimens  gave  the  following  average  results  (eighteen  tests  on 
each  material) : 


Material. 

Modulus  of 
Elasticity. 

True  Elastic 
Limit. 

Apparent 
Elastic  Limit. 

Ultimate 
Strength. 

Per  cent 
of  Elon- 
gation. 

Reduc- 
tion of 
Area 

Low  steol  
Wrought  iron  .  , 

f,bs.  per  sq.  in. 
81.000,000 
28,600,000 

Lbs.  per  sq.  in. 
28,500 
21,800 

Lbs.  per  sq.  in. 
36,600 
33,000 

Lbs.  per  sq.  in. 
61,000 
52,200 

jgin  8 
"    27.8 
160 

59.3 

2.1.4 

398 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG.  323. — Showing  Relative  Resistance  to  Shock  of  Wrought  iron  and  Basic  Bessemer 
Steel  Bars  which  hail  been  Grooved  on  the  Tension  Side  to  a  depth  of  0.06  in. 
(Tetmajer,  vol.  iv.  PI.  X.)  W  =  wrought  iron,  S  =  steel.  The  hammer  weighed 
660  Ibs.  and  fell  9  in.,  19  in.,  "29  in.,  51  in.,  uud  79  in.,  for  the  five  sizes  respectively, 
the  span  being  always  40  in.  The  number  of  blows  were  2,  3,  2,  2,  1,  4,  1,  7,  1, 
and  6  for  the  ten  specimens  as  shown  above,  respectively. 


_j 

»  o  a 
oTS"  *» 

ET.^- H   :  * 


COLD-BENDING   AND  DRIFTING   TESTS. 


399 


The  great  superiority  of  the  steel  in  the  impact  tests  is  evident  from  the 
figure. 

In  the  cold-bending  tests  on  the  same  forms,  flatwise,  the  steel  specimens 
0.8  inch  thick  folded  flat  without  sign  of  rupture,  while  those  1.2  inches 
thick  cracked  in  flattening  down.  The  wrought-iron  specimens  0.8  inch 
thick  cracked  after  bending  through  an  angle  of  120°,  and  the  1.2-inch 
specimens  after  bending  through  an  angle  of  60°. 

305.  Comparison  of  Results  of  Cold-bending  Tests  with  the  Tensile 
Strength  and  the  Percentage  of  Elongation. — In  Bacle's  report  on  Various 
Cold  Tests  of  Materials,  in  the  French  Commission  Report,  vol.  in.  p.  311, 
are  given  the  mean  results  of  several  thousand  tests  in  tension  and  cold  bend- 
ing on  wrought  iron  and  soft  steel,  received  from  many  different  sources, 
made  by  M.  Hallopeau,  a  member  of  that  Commission,  and  given  in  the  fol- 
lowing tables.  These  results  are  not  only  of  great  value  for  the  information 
itself,  but  they  will  serve  to  enable  one  to  prepare  standard  specifications  for 
cold-bending  tests  from  the  relation  of  the  results  of  these  to  the  results  of 
tension  tests  which  have  long  been  the  standard  tests  of  acceptance  in  this 
country. 

TABLE    XVIII. RELATIVE    RESULTS    OF  TESTSIOX   AXD  COLD-BEN'DIXG  TESTS. 


Tension  Test. 

Bending  Test. 

Material. 

Elastic  Limit. 

Ultimate 
Strength. 

Elonga- 
.    tion. 

Cracked 
at  Angle 
of 

Ruptured 
at  Angle 
of 

Wrought  iron   with  grain 

Lbs.  per  sq.  in. 
32  000 

Lbs.  per  sq.  in. 
48  500 

Percentage 
14  0 

Degrees. 
80 

Degrees. 
30 

"            "     across   "     

30,000 

42,000 

6.5 

130 

115 

Low  steel  (57,000  to  60,000  T.  S.) 

29,500 

60,000 

27.0 

0 

0 

Medium  steel  (64,000  T.  S.)  

34,000 

65,000 

25.0 

0 

0 

High  steel  (08,500  to  71,  SOOT.  S.) 

35,500 

72,000 

24.0 

0 

0 

The  tension-test  bars  were  4  in.  long,  1.6  in.  wide,  and  0.4  in.  thick. 
The  bending-test  bars  were  6  in.     "      1.6  in.      "         "    0.4  in.       " 
The  bending-test  angle  of  record  is  the  angle  formed  by  the  two  ends  of  the  bar  after 
bending,  or  it  is  the  supplement  of  the  angle  through  which  bending  has  taken  place. 

It  will  be  seen  from  the  above  table  that  while  the  bending  test  would 
serve  to  distinguish  varying  qualities  of  wrought  iron,  it  would  riot  serve  to 
distinguish  these  three  grades  of  steel,  since  they  all  bent  through  180°  and 
folded  flat  without  even  cracking.  Since  these  grades  require  distinction  in 
practice  because  of  the  different  degrees  of  injury  produced  on  them  by 
punching,  the  specimens  can  be  punched  and  then  bent,  and  the  shades  of 
hardness  indicated  by  the  greater  angles  at  whicli  cracks  appear.  This  has 
been  done  by  M.  Hallopeau,  and  the  results  are  shown  in  Table  XIX.  The 
plates  were  all  the  same  size  as  those  given  in  the  previous  table,  the  punched 
and  drilled  holes  being  0.8  inch  in  diameter,  or  one  half  the  "width  of  the 
bar,  the  thickness  being  0.4  inch.  The  die  side  of  the  plates  was  made  the 
tension,  or  convex,  side. 


400 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE  XIX.  — EFFECTS  OF  PUNCHING  AND  DRILLING  ON  WROUGHT  IRON 
AND  STEEL,  AS  DETERMINED  BY  TENSION  AND  COLD-BENDING  TESTS 
ON  BARS  0.4  INCH  THICK. 


Material. 

Tension  Test. 

Bending  Test. 

Elastic 
Limit. 

Ultimate 
Strength. 

Elonga- 
tion. 

Cracked 
at  An- 
gle of 

Rupt'd 
at  Angle 
of 

WROUGHT   IRON. 

Plain. 
,  (  With  the  "-niiii   . 

Lbs. 
per  sq.  in. 

32,000 
30,000 
20,000 
26,500 
33,500 
39,000 
28,500 
28,500 

29,000 
26,000 
42,000 
29,000 

Lbs. 
per  sq.  in. 

48,500 
42,000 
47,000 
41,000 
53,000 
46.000 
47,000 
41,500- 

38,500 
32,000 
46,000 
34,000 
56,000 
38,000 
43,500 
37,500 

42,000 
36,000 
44.500 
33,000 
54,000 
44,000 
41,000 
35,000 

60,500 
59,000 
65.500 
59,000 

60,000 
55,000 
67,500 
58,000 

60,200 
59,700 
67,000 
59,700 

Percent- 
age. 

14.0 
6.5 
19.8 

8.3 
15.0 
3.3 
16.7 

7.7 

1.0 
1.0 
2.4 
1.0 

l'.6 
1.5 

2.7 
1.5 
3.3 
1.8 
1.8 
0.8 
3.2 
1.5 

27.0 
27.8 
22.4 
30.0 

4.5 

4.6 
4.1 
5.0 

6.8 
7.4 
68 
7.1 

Degrees. 

80 
130 
65 
115 
80 
135 
100 
105 

175 
180 
170 
175 
175 
178 
170 
175 

172 

177 
176 
177 
175 
177 
172 
178 

100 
90 
150 
90 

45 
40 
110 

20 

Degrees. 

30 
115 
20 
85 
40 
100 
50' 
80 

150 
175 
150 
165 
160 
175 
150 
165 

165 
172 

172 
173 
168 
173 
165 
175 

60 
59 
135 
60 

10 

100 
10 

Natural  \  Across  tof  grain.  .........  ..... 

(  W"ith  the  °'raiu 

Annealed  -j  Acrogs  lhcrffrain             

Hardened  in  water|S^|™-::;:. 
Hardened  and  annealed  |  SsstL^lin. 

Punched. 
,  (  With  the  o-raiu.  . 

Natural  j  ^TOSB  theegrain.  .  .  .  ....     ..'.'. 

t    ^  (  With  the  12:  rain  .. 

AnDealed  |  Across  the  graii  ..      . 

(  With  the  crain 

Hardened  in  water  J  Aci.()ss  ,^8gl,,in;   ... 
Hardened  and  annealed|S^|^; 

Drilled. 
,  (  With  the  erram 

33,500 
29^500 

28,500 
25  000 

NaturaM  Across  the  grain     

29,000 
24,500 
36,500 
30,000 
29,500 
27,000 

29  500 

Amiealed  |  Across  thl  grain 

Hardened  in  water  )  ^'-ifcain.n...... 
Hardened  and  annea,ed|Wit1,stheeg™n... 

LOW  STEEL. 
Plain. 
Natural  

An  nealed  

28  500 

Hardened  in  water  

34,000 
29,000 

36,200 
36,500 
45,000 
36,400 

36,000 
34,200 
39,200 
33,500 

Punched. 
Natural  

Hardened  in  water  

Hardened  and  annealed 

Drilled. 
Nat  u  ral  

Annealed  

Hardened  in  water  

Hardened  and  annealed  

COLD-BENDING  AND  DRIFTING   TESTS.  401 

EFFECTS   OF   PUNCHING   AND    DRILLING    ON    WROUGHT    IRON   AND 

STEEL — continued. 


Material. 

Tension  Test.                         Bending  Test. 

Elastic 
Limit. 

Ultimate 
Strength. 

Finn,    i    ,  Cracked  |  Rupt'd 
S         atAn-    :»t  Angle 
lon-       gle  of           of 

MEDIUM  STEEL. 
Plain. 

Lbs. 
per  sq.  in. 

34,000 
32,800 
37,000 
33,800 

36,500 
35,500 
51,000 
37,000 

36,500 
35,500 
51,000 
36,000 

35,500 
36,200 
43,500 
35,500 

47,000 
47,500 
71,000 
47,000 

39,700 
38,600 
56,700 
39,000 

Lbs. 
per  sq.  in. 

65,500 
64,000 
73,500 
66,000 

67,000 
64,000 
77,000 
64,500 

66,000 
64,500 
73,000 
65,000 

72,000 
70,000 
80,000 
71,300 

72,000 
71,000 
80,000 
71.000 

71,800 
69,000 

82,000 
71,600 

Percent- 
age. 

25.0 

26.8    : 
23.8    ! 
26.0 

4.5 

4.7 
2.2 
4.7 

6.2 
6.5 
6.3 
6.5 

24.0 
25.0 
20.0 
25.0 

3.9 
3.4 
3.4 
3.4 

5.5 
5.6 

5.8 

5.7 

Degrees. 

100 
95 
145 

100 

70 
65 
100 
60 

20  to  60 

140 
120 
160 
135 

80 
70 
140 
85 

Degrees, 

80 
75 
130 

75 

50 
40 
80 
40 

105 
95 
145 
105 

60 
55 
125 
60 

Hardened  in  water              .  .              .        . 

Hardened  and  annealed  

Punched. 
Natural  

Annealed                    

Hardened  in  water     

H'li'deued  and  annealed                      •  .  • 

Drilled. 
Natural  .       

Hardened  in  water 

Hardened  and  annealed  .  . 

HIGH  STEEL. 
Plain. 
Natural  

Annealed       .    .          .  .  .    . 

Hardened  in  water       

Hardened  and  annealed  

Punched. 
Natural     .  .    . 

Hardened  in  water                   . 

Hardened  and  annealed  

Drilled. 

Natural                                                    < 

Annealed       .                      ........ 

Hardened  in  water  

Hardened  and  annealed  

NOTE. — All  the  bars  were  1.6  in.  wide  and  D.4  in.  thick.  The  elongation  in  the 
tension  test  was  measured  on  a  length  of  4  in.  with  both  the  plain  and  the  punched  or 
drilled  specimens.  In  the  former  case  this  elongation  occurred  throughout  this  entire 
distance  (4  in.),  while  in  the  latter  it  occurred  only  in  the  vicinity  of  the  hole,  but  was 
credited  to  the  entire  distance  of  4  inches  in  computing  the  percentage  of  elongation. 
These  percentages  are  therefore  not  comparable  as  showing  loss  of  ductility  (as  has  been 
assumed  in  the  Rep.  French  Com.). 

The  bending-test  angle  of  record  is  the  angle  formed  by  the  two  ends  of  the  bar  after 
bending. 


402  TEE  MATERIALS  OF  CONSTRUCTION. 

The  following  conclusions  may  be  drawn  from  Table  XIX : 

1.  The  reduced  ductility  of  wrought  iron  across  the  grain  is  fully  brought 
out  both  in  the  elongation  of  the  tension  tests  and  in  the  angles  of  rapture 
in  the  cold-bending  tests, 

2.  The  weakening  effect  of  both  punching  and  drilling  is  very  much 
greater  with  the  wrought  iron  than  with  the  soft  and  mild  steels,  and  some- 
what greater  than  it  is  on  the  medium  steel. 

3.  The   annealing   of  the  punched  specimens  in  no  case  appreciably 
increased  their  ductility,  as  shown  by  both  the  tension  and  the  bending 
tests.     It  increased  the  strength  of  the  wrought-iron  specimens  somewhat, 
but  it  lowered  the  strength  of  the  steel  specimens. 

4.  The  drilled  specimens  of  wrought  iron  do  not  differ  appreciably  from 
the   punched  either  in    strength  or  ductility,  while  with  the  steel  of  all 
grades  the  ductility  of  the  drilled  specimens  is  far  greater  than  that  of  the 
punched  specimens,  although  the  ultimate  strength  is  the  same. 

5.  The  change  from  65,000-  to  72,000-lb.  steel  is  very  clearly  indicated 
by  the  bending  test,  where  in  the  punched  specimen,  "  natural,"  the  angle 
through  which  the  specimen  bent  before  cracking  is  100$  greater  with  the 
former  than  with  the  latter.     No  such  difference  appears  as  between  the 
60,000-lb.  and  the  65,000-lb.  steel,  showing  that  they  are  about  equally  well 
adapted  to  such  work.     In  the  "  plain  "  specimens  all  three  grades  of  steel 
closed  down  entire  (angle  —  0)  without  sign  of  failure,  thus  manifesting  no 
difference  in  hardness.     The  bending  test  on  punched  specimens,  therefore, 
develops  clearly  this  difference  in  fitness  for  riveted  construction,  and  it 
might  well  be  used  as  a  shop-criterion  of  acceptance.     Thus  the  60,000-lb. 
and  the  65,000-lb.  steels  bent  through  an  angle  of  80°  after  punching  before 
a  crack  appeared,  while  the  72,000-lb.  steel  bent  through  an  angle  of  only 
40°  before  cracking.     If  an  angle  of  60°  were  specified  on  this  test  for  plates 
0.4  in.  thick  (leaving  an  angle  of  120°  formed  by  the  two  ends  of  the  bar) 
before  a  crack  should  appear,  it  would  seem  to  rule  out  the  higher  carbon- 
steels,  which  are  injured  by  punching  and  shearing.     This  angle  would  be 
different,  however,  for  different  thicknesses  of  plate. 

306.  Combined  Specified  Requirements  in  Tension  and  Cold  Bending.— 
The  combined  requirements  given  in  Table  XX  are  reproduced  from  the 
Report  of  the  French  Commission,  vol.  in.  pp.  342-353.  While  the  joint 
requirements  of  many  French  government  bureaus  are  there  given,  only 
those  of  the  Ar tiller ie  de  terre  are  here  given. 

The  Committee  of  the  American  Society  of  Civil  Engineers  has  recom- 
mended (1896)  the  following  cold-bending  tests  of  plain  specimens: 

Wrought-iron  specimens  should  bend  through  90°  without  fracture,  with  inner 
radius  not  exceeding  twice  the  thickness  of  the  test  specimen  for  bar-iron  nor  three 
times  that  thickness  for  plate  and  shape  iron. 

Rivet-iron  and  Rivet-steel  bars,  when  heated  to  a  low  cherry-red  and  quenched 
in  water  (this  for  the  steel  bars  only),  must  bend  through  180°  to  a  close  contact 
(radius  =  0)  without  sign  of  fracture. 


COLD-BENDING  AND  DRIFTING   TESTS. 


403 


Low  Steel  (60,000  Ibs.  T.  S.),  when  treated  in  the  same  manner,  must  bend  to  a 
2ero  angle  (through  180°),  with  an  inner  radius  equal  to  the  thickness  of  the  speci- 
men, without  sign  of  fracture. 

Medium  Steel  (65,000  Ibs.  T.  S.)  specimens,  cut  from  bars,  plates,  or  structural 
forms,  in  their  natural  state,  must  bend  through  180°,  with  an  inner  radius  equal  to 
one  and  one-half  times  the  thickness  of  the  specimen,  without  sign  of  fracture. 

Hiyh  Steel  (70,000  Ibs.  T.  S.)  specimens,  cut  from  plates  and  forms,  in  their  natu- 
ral state,  must  bend  through  180°  to  an  inner  radius  equal  to  twice  the  thickness  of 
the  specimen  without  showing  sign  of  fracture. 

TABLE    XX. — COMBINED    REQUIREMENTS    IN   TENSION    AND    COLD    BENDING. 


Material. 

Tension. 

Thick- 
ness 
of 
Speci- 
men. 
t 

Cold  Bending. 

Ultimate 
Strength. 

Elonga- 
tion. 

Angle 
before 
Cracking. 

Radius 
of  Bend. 

0.5Z 
0.5Z 
1.5  to  2.0* 
2t 
0  5t 
0.5Z 

0 
0  to  1.5* 

0 
0 
0 
1.5* 

t 

0 
0 

0 

<* 
0 

t 

WKOTJGHT  IRON. 

Rolled  Forms  (Round  and 
Rectangular). 

First-class  charcoal  iron,  threaded1 
First-class  puddled  iron,  threaded 
Good                "           "      plain  .... 
Common                                  "  . 

Lbs.  per  sq.  in. 

48,500 
48,500 

48,'  500 

5o!66o 

50,000 

48,000  to  60,000 
48,000  to  64,000 

57,000  to  68,500 

60,000  to  71,000 
57  000  to  68  500 

Per  cent. 
25 
25 

'25' 

io' 

10 

.... 

26 
23  to  25 

22 

21 
21  to  23 

In  inches 
t  <  1.6 
t  <  1.6 
t  <  1.64 

t  <  6.6 
t^  0.6 

t  <  0.4 
t  <  0.4 

«0.2 
>0.2 
r<0.4 
«.08 
y>  .08 
'<0.2 
,>  0.2 
1  <0.4 

any  t 
any  t 

t  <0.2 
t>  0.2 
t  <  0.2 
t  >  0.2 

Degrees. 
0* 
O3 
0 
90 
0 
90 

0 
0 

0 

j-  90 
0 

\    « 
|  so 

0 
0 

0 
0 
0 
0 

Iron  for  bolts   threaded 

Plate  Iron.5 
WITH   THE   GRAIN. 

First-class  charcoal  iron  

ACROSS   THE    GRAIN. 

Refined  puddled  iron  .  .    -     

a             «          n 

STRUCTURAL  STEEL. 
Low  and  Medium. 
Rolled  forms  hardened 

Plates,6 

High  Steel. 
Rolled  forms,  hardened  

Plates,5                             

1.  Screw-threads  cut  on  bar  where  the  bending  occurs,  ns  shown  in  Fig.  324. 

2.  This  is  the  angle  formed  by  the  two  ends  of  the  bar  after  bending. 

3.  Some  cracks  are  allowed  here  at  the  bottoms  of  the  threads. 

4.  When  the  iron  has  a  greater  thickness  than  1.6  in.  it  is  to  be  cut  down  to  this 
thickness. 

5.  Specimens  sheared  off  and  filed  up  smooth. 

307.  Comparison  of  Tension,  Impact,  and  Cold-bending  Tests.— It  will  be 
seen  from  the  following  tables  that  the  loss  of  ductility  in  punching  iron 


404 


THE  MATERIALS  OF  CONSTRUCTION. 


and  steel  plates,  and  the  benefit  of  subsequent  annealing,  are  best  developed 
by  impact  tests.  Also,  the  benefits  of  enlarging  punched  holes  by  boring 
and  reaming.  The  tables  are  compiled  from  M.  Hallopeau's  experiments 
described  above,  and  are  given  in  Eep.  Fr.  Com.,  pp.  356-7. 

These  test-bars  were  8  in.  long,  2.4  in.  wide,  and  0.32  in.  thick.  The 
punched  and  drilled  holes  were  0.8  in.  in  diameter,  or  one  third  the  width 
of  the  plates.  The  hammer  used  in  the  impact  test  weighed  88  Ibs.,  and  it 
had  a  constant  fall  of  16  in.  .  The  average  sums  of  all  the  heights  of  fall 
before  cracks  appeared  are  given  in  the  table.  The  figures  given  are  the 
average  results  of  many  tests. 

TABLE   XXI. — COMPARISON   OF    RESULTS   BY   TENSION,   IMPACT,   AND    COLD- 
BENDING   TESTS   ON.  PUNCHED   AND   DRILLED    PLATES. 


Tension  Tests 

Impact  Tests. 

Cold-bending  Tests. 

on 
the  Plain  Specimens. 

Total  Height  of 
Drops. 

Angles  when 
Cracks  appeared. 

Holes  Punched. 

Holes  Punched. 

Material. 

i 

0.04  in. 

0.04  in. 

1 

i 

a 

i 

small.* 

I 

small. 

3 

_o 

a 

99 

N 

'Z 

| 

§ 

•d 

MN 

&0 

03 

CQ 

"3  .i 

B~ 

CO 

*& 

c^ 

a 

OJ  « 

C  3 

3 

g 

w 

O 

M 

1 

I5 

So 

o 
ffi 

i 

1° 

go 

Ibs.  sq.  in. 

Ibs.  sq.  in. 

% 

in. 

in. 

in, 

in. 

deg. 

deg. 

deg. 

deg. 

Wrought  iron,  natural.  . 
"      annealed 

39,000 

55,000 

14.0 

32 
37 

16 
37 

27 
43 

32 
37 

173 
173 

177 
173 

174 
172 

174 
173 

Steel   natural.  ,  

43,500 

59  500 

99  5 

108 

6? 

85 

77 

164 

168 

165 

166 

"     annealed 

130 

107 

128 

112 

159 

161 

160 

161 

*  This  is  too  small  an  enlargement  to  remove  the  material  injured  by  punching,  and 
hence  these  results  do  not  fully  develop  the  differences  of  treatment.— J.  B.  J. 

TABLE   XXII.— COMPARISON   OF   RESULTS   OF   THE   IMPACT   TESTS. 


Relative  Treatment  of  Specimens. 

Wrought  Iron. 

Steel. 

Annealed. 

Not 
nnealed. 

O3   ^ 
0)  iX» 

II 

1 

T3 
V 

If 

<J 

Excess  of 
Annealed. 

Drilled  full  size  

inches. 
37 
43 
37 
37 

inches. 
32 
27 
32 
16 

& 

59 
14 
130 

inches. 
130 
128 
112 
107 

inches. 

108 
85 

77 
62 

% 

20 
50 
45 

72 

Punched  0  04  in  *  small  and  drilled  out  

Punched  0.04  in.*  small  and  reamed  out  

Superiority  of  drilling  over  punching      •  •  • 

*0 
16 
0 

100 
69 
100 



% 
21 
20 
5 

% 
74 
37 
24 

*  See  note  following  Table  XXI. 


COLD-BENDING  AND  DRIFTING   TESTS. 


405 


The  following  are  some  of  the  more  important  conclusions  to  be  drawn 
from  Tables  X.XI  and  XXII: 

1.  The  great  superiority  tinder  impact  of  the  steel  over  the  wrought-iron, 
with  all  kinds  of  treatment. 


Fro.  324.— Cold-bending  Tests  of  Best  Wrought-iron,  1  in.  to  2  in.  in  diameter.     (From 

Rep.  U.  S.  Test  Board,  1881,  vol.  i.) 

2.   The  excess  in  strength  of  the  annealed  over  the  unannealed  speci- 
mens in  all  cases,  with  both  iron  and  steel. 


406 


THE  MATERIALS  OF  CONSTRUCTION. 


3.  The  superiority  of  drilling  over  punching  in  all  cases,  this  being  100$ 
-with  the  wrought-iron  and  74$  with  the  steel  plates,  under  the  impact  tests. 

4.  The  great  benefits  of  enlargement  of  punched  holes  by  drilling  or 
reaming,  this  being  an  average  of  85$  with  the  wrought-iron  and  30$  with 
the  steel  plates,  when  the  thickness  of  plates  was  0.32  in.  and  the  enlarge- 
ment only  0.04  in. 

With  greater  thicknesses  of  plate  the  superiority  of  steel  over  iron  would 
probably  be  somewhat  less,  while  the  differences  indicated  in  2,  3,  and  4 
would  be  greatly  increased.  With  a  greater  enlargement  of  punched  holes, 
also,  the  benefits  of  reaming  would  be  much  more  marked,  especially  on  the 
.steel  plates. 

DRIFTING   TESTS. 

308.  Their  Character  and  Significance.— These,  like  the  cold-bending 
tests,  are  such  ns  may  be  applied  in  the  workshop  and  by  the  workmen 

themselves  with  their  ordinary  shop  appli- 
ances. The  test  consists  in  punching  or 
boring  holes  of  given  diameters  (varied  with 
the  thickness  of  the  plate)  at  given  distances 
from  the  edge  of  the  plate  or  structural 
form,  and  then  enlarging  it  by  driving  in  it 
a  drift-pin,  as  shown  in  Fig.  325,  the  per- 
centage of  enlargement  without  cracking 
being  a  very  good  indication  of  the  ductility 
of  the  metal.  To  serve  as  a  criterion  of 
comparison,  however,  it  must  be  reduced  to 
fixed  rules,  the  same  as  all  other  kinds  of 
tests. 

A  specification  commonly  used  in  France 
is  as  follows  :* 

Wrought-iron  bars  shall  be  cut  both  with  and 
across  the  grain,  3  in.  wide,  and  three  holes 
punched,  f  in.  in  diameter  and  2f  in.  apart,  along 
the  central  line  of  the  plate.  These  holes  shall  then 
be  enlarged,  beginning  with  the  central  one,  and 
using  a  drift-pin  which  increases  its  diameter  at 
the  rate  of  1  in  10.  Plates  0.20  in.  thick  should 


FIG.  325. — Drifting  Test  on  ^-in. 
Steel  Angle.  A  jf  in.  Hole 
Drifted  to 

(Engr.    News,    vol.   xxxm.    p 
272.) 


in  in  Diimpfpr  submit  to  an  enlargement  of  the  f-in.  hole  to  a 
'  diameter  of  1  in.;  plates  0.25  in/  thick  should 
.enlarge  to  1.2  in.  diameter;  plates  0.30  in.  thick 
'should  enlarge  to  1.32  in.  diameter;  and  plates 
thicker  than  0.32  in.  should  enlarge  to  from  1  in.  to  1.3  in.,  according  to  quality, 
without  showing  any  sign  of  failure. 

Steel  plates,  "similarly  prepared,  of  57,000  Ibs.  tensile  strength  should  enlarge  to 
1.6  in.  diameter  after  annealing  and  to  1.5  in.  diameter  after  hardening  in  water. 
Steel  plates  of  57,000  to  64.000  Ibs.  tensile  strength  should  allow  a  fin.  hole  to 
enlarge  to  1.5  in.  diameter  after  annealing  and  to  1.4  in.  diameter  after  hardening 

in  water.  _^ 

*  That  of  the  Eastern  Railway  CoinpaDy. 


CHAPTER  XXI. 
THE  TESTING  OF  CEMENT. 

309.  The  Standard  Scientific  Tests  of  Cement  are  those  which  are  made 
to  determine  the  following  properties : 

(a)  Strength,  neat  and  with  different  proportions  of  sandy 

(b)  Fineness  of  grinding ; 

(c)  The  thoroughness  of  the  burning; 

(d)  The  rate  of  setting; 

(e)  The  permanency  of  volume,  commonly  called  the  test  for  "  sound- 

ness." 

The  strength  of  cement  and  of  cement-mortar  is  usually  determined 
by  the  tensile  test  on  small  shapes,  called  briquettes,  which  have  hardened 
under  water  for  varying  periods  of  time.  The  more  common  periods  are : 
for  natural  cement,  one  day  and  seven  days ;  for  Portland  cement,  seven  days 
and  twenty-eight  days.  It  is  well,  however,  to  extend  the  time  of  setting  to 
a  longer  period  if  practicable.  Since  natural  cement  usually  sets  and 
hardens  more  rapidly  than  Portland  cement,  it  is  sometimes  used  in  place  of 
the  Portland,  where  but  a  short  period  of  time  can  be  allowed«for  the  test- 
ing. Thus  for  street  improvements  the  material  is  usually  tested  after  it  is 
brought  upon  the  works,  that  is  to  say,  placed  upon  the  sidewalks;  and  as  it 
here  forms  a  serious  obstruction,  it  is  desirable  to  have  the  tests  made  in  as 
short  a  time  as  possible.  Since  the  one-day  test  for  a  quick-setting  natural 
cement  will  indicate  its  quality,  such  a  material  is  often  used  solely  on  this 
account. 

Although  cement  is  more  commonly  subjected  to  compression,  yet  it  has 
been  found  that  the  tensile  test  effectually  indicates  the  compressive  strength 
(see  Fig.  337).  This  holds  true  both  for  the  neat  cement  and  for  cement- 
mortars. 

Since  cement  is  always  used  mixed  with  sand,  some  of  the  highest  authori- 
ties are  now  advocating  the  abandonment  of  the  neat-cement  tests  for 
strength  and  making  the  strength  test  on  a  mortar  containing  three  of  sand 
to  one  of  cement,  by  weight,  in  the  case  of  Portland  cement,  and  two  of 
sand  to  one  of  natural  cement,  by  weight,  these  being  the  usual  proportions. 
For  special  purposes  four  or  five  parts  of  sand  may  also  be  employed, 

407 


408 


THE  MATERIALS  OF  CONSTRUCTION. 


especially  with  finely-ground  cements,  or  such  as  give  a  residue  of  less  than 
10  per  cent  on  a  sieve  having  14,400  meshes  per  square  inch  (2300  per  square 
centimeter).  Since  in  the  sand  mixtures  a  standard  sand  must  be  employed, 
it  has  become  customary  to  use  clean,  sharps  and  which  has  passed  a  No.  10 
sieve  (20  meshes  per  linear  inch),  and  stopped  on  a  No.  30  sieve  (30  meshes 
per  linear  inch).  In  order  to  further  insure  identity  of  the  sand  used,  the 
American  Society  of  Civil  Engineers,  has  recommended  that  crushed  quartz 
be  used,  such  as  is  employed  in  the  making  of  sandpaper.  The  author  does 
not  favor  this'practice.  This  material  has  fully  50  per  cent  of  voids,  while 
the  ordinary  sands,  with  roughly  rounded  grains,  contain  but  about  33  per 
cent  of  voids.  Any  good,  sharp,  clean  sand,  therefore,  of  the  size  20-30 
should  give  very  nearly  uniform  results  which  will  average  much  higher 
than  those  obtained  with  crushed  quartz,  unless  the  quartz  briquettes  be 
thoroughly  compacted  by  hard  hammering. 

All  tensile- test  briquettes  of  Portland  cement  (neat  or  with  sand)  should 
be  kept  in  a  moist  atmosphere  for  24  hours,  and  then  kept  the  remainder  of 
the  period  under  water.  Natural  cements  are  kept  from  one  to  four  hours 
in  air  (or  till  they  have  set)  and  then  put  in  water. 

The  importance  of  maintaining  the  water  for  mixing,  and  for  the  bath 
during  the  entire  hardening  period,  at  a  standard  temperature,  in  order  to 


O  SO  7^ 

FIG.  326.— Effect  of  Temperature  of  Cement  on  Time  of  Setting.     (Wheeler,  Rep.  CJtf. 

Engrs.,  1895,  p.  2936.) 

obtain  uniform  results,  is  clearly  shown  by  Figs.  326  and  327.  In  the 
former  it  is  shown  that  the  time  of  setting  is  greatly  shortened  by  increasing;: 
the  temperature  of  the  mixing  water,  while  Fig.  327  indicates  that  the 
strength  attained  in  a  given  time  may  be  greatly  increased  by  raising  thei 
temperature  of  the  bath  from  40°  to  80°  F.  In  the  case  of  normal  mortar,} 
1C.  :  3S.,  this  increase,  at  two  months,  was  from  100  Ibs.  to  230  Ibs.  per? 
square  inch.  The  Fifth  International  Convention  for  Unifying  the  Methods? 


TESTING   OF  CEMENT. 


409 


of  Testing  Materials  (Zurich,  Sept.  1895)  decided  that  it  was  not  advisable 
to  hasten  the  hardening  process  by  raising  the  temperature  of  the  bath, 
since,  after  numerous  trials,  uniform  results  could  not  be  obtained. 


400 


300 


^*-K 


:: 


L---x 


4  T  L 


ft 


J?IG.  327.— Showing  Effect  of  Temperature  of  Immersing  Tanks  on  the  Rate  of  Harden- 
ing of  Natural  Cement-mortar.     (Wheeler,  Rep.  Chf.  Engrs.,  1894.) 

310.  The  Fineness  of  the  Grinding  is  determined  by  passing  the  cement 
through  sieves  of  a  specified  number  of  meshes  to  the  lineal  inch.     While 


M 

I 


N 


FIG.    328. — Showing  Absence  of   Cementing  Properties  of   the   Coarser  Particles  of 
Cement,  1  C.  :  3  S.,  age  4  mos.     (Jour.  Assoc.  Eng.  tiocs.,  vol.  xiv.  p.  245.) 

the  size  of  such  meshes  would  of  course  depend   on  the  diameter  of  the 
wire  used,  it  is  difficult  to  determine  this  diameter,  while  the  counting  of 


410 


TEE  MATERIALS  OF  CONSTRUCTION. 


the  meshes  is  practicable.  It  has  been  found  by  experiment,  Fig.  328,  that 
only  the  finest  or  most  impalpable  dust  is  really  active  in  the  setting  and 
hardening  of  the  cement,  the  coarser  grains  acting  as  so  much  inert  matter, 
which  might  as  well  be  replaced  by  sand.  The  proportion  of  the  cement 
which  passes  a  sieve  of  less  than  about  100  meshes  to  the  lineal  inch  does 
not  give  any  intelligent  idea  of  the  significant  fineness  of  the  grinding.  In 
fact  the  standard  sieve  for  determining  fineness  now  generally  used  on  the 
continent  of  Europe  has  seventy  meshes  per  lineal  centimeter,  which  corre- 
sponds to  175  meshes  per  lineal  inch,  or  over  30,000  meshes  per  square  inch. 
Not  more  than  about  twenty-five  per  cent  of  the  cement  should  be  held  on  a 
sieve  of  this  degree  of  fineness.*  The  author  of  this  work  recommends  that 
a  sieve  of  120  meshes  per  linear  inch  (14,400  per  square  inch)  be  used,  and 
that  the  residue  on  this  sieve  shall  not  be  more  than  twenty  (20)  per  cent. 
This  requirement  can  now  be  readily  complied  with  by  all  the  leading  manu- 
facturers of  Portland  and  slag  cements,  f 

The  French  Commission  advocate,  in  testing  for  fineness — 
1.  Separating  it  into  four  grades  by  using  sieves  as  follows: 


Approximate 
Number  of 

Number  of  Open- 
ings per  Linear 

Number  of  Open- 
ings per  Square 

Size  of  Wire 

Size  of  Openings 

Sieve. 

Inch. 

Centi- 
meter. 

Inch. 

Centi- 
meter. 

In  Inches. 

In  Milli- 
meters. 

In  Inches. 

In  Milli- 
meters. 

50 

50 

18 

2,500 

324 

0.08 

0.20 

0.014 

0.36 

80 

80 

30 

6,400 

900 

0.06 

0.15 

0.007 

0.18 

175 

175 

70 

32,400 

4,900 

0.02 

0.05 

0.0035 

0.09 

2.  This  test  to  be  made  on  a  sample  of  100  grams,  with  sieves  about 
12  inches  in  diameter. 

3.  Hand-sifting  to   be    considered    finished   when    not  over  0.1   gram 
passes  under  the  action  of  25  movements. 

4.  The  employment    of  a  shaking-machine  is  recommended,  especially 
for  the  No.  175  sieve. 

5.  The  results  should  be  given  as  the  total  percentages  which  failed  to 
pass  each  sieve,  beginning  with  the  finest.     Thus  the  percentage  held  by 
the  Xo.  175  sieve  includes  the  percentages  stopped  on  the  other  two,  and 
the  percentage  given  for  the  No.  80  sieve  would  include  that  held  on  the 
No.  50  sieve. 

*  It  has  beeu  customary  in  the  United  States  to  specify  a  sieve  of  50  meshes  per 
lineal  inch,  but  occasionally  a  sieve  of  100  meshes  per  inch  has  been  used.  The  former 
size  has  no  significance  whatever  in  determining  that  degree  of  fineness  requisite  to 
proper  action  of  the  cement,  and  the  latter  is  too  coarse  to  have  much  or  any  value. 

f  This  is  also  the  standard  chosen  by  Mr.  J.  W.  Sandemau,  M.  lust.  C.  E.,  in  Trans. 
Inst.  C.  E.,  vol.  cxxi.  (1894-5)  p.  215,  and  it  has  also  been  adopted  by  some  officers  o£ 
the  U.  S.  Engr.  Corps. 


TESTING   OF  CEMENT. 


411 


Ox 

x 

(f 

[x^ 

^?^? 

/^ 

/ 

7 

S|/T/, 

)„-•** 

/ 

x: 

(/>> 

4OO 

/    f 
\  / 
x/* 

.--«'-« 

ses- 

/ 

/ 

T^ 

^ 

7*t2 

-'•-' 

^ 

2OO 

if 

,rr£ 

<l^ 

^ 

^ 

v 

/ 

«?£/ 

K  /f/ 

'/W 

0 

6000 


20 


FIG.  339.—  Showing  Effect  of 
Sifting  a,  Coarse  Portland 
Cement  through  a  No.  180 
mesh  sieve  (Trans.  Inst. 
C.E.,  vol.  84.) 


2m  3Y#. 

FIG.  330. — Showing  the  Greater  Efficiency  of  Very 
Finely  Ground  Cements  when  mixed  with  Three 
Parts  of  Sand.  (Tetmajer.) 


£00 


FIG.  331.—  Showing  Effect  of  Kegrinding  Portland  Cement  on  Mortar,  1  C.  : 
grinding  left  only  6.5%  on  a  No.  175  sieve  (30,000  meshes  per  square  in 
second  grinding  it  all  passed  this  sieve.  (Tetmajer,  vol.  VH.) 


3  S. 
inch). 


First 
After 


THE  MATERIALS  OF  CONSTRUCTION. 


Dr.  W.  Michaelis,  the  great  German  specialist,  recommends  *  that  two 
sieves  be  used,  Xo.  75,  and  No.  150  (30  and  GO  meshes  per  cm.),  and  in 
addition  to  these  the  Schone  washing  apparatus  with  rates  of  upward  flow  of 
the  alcohol  of  2.8  inches  per  minute,  giving  particles  of  cement  which  would 
pass  a  No'.  300  sieve  (120  per  centimeter),  and  also  of  1  inch  per  minute 
upward  velocity,  giving  particles  which  would  correspond  to  those  passing  a 
No.  GOO  sieve  (240  meshes  per  centimeter).  This  washing  process,  added  to 
the  use  of  the  two  sieves,  would  enable  one  to  graduate  the  cement  as 
follows: 


Number  of  Meshes  per 

Diameter  of  Wire 

Width  ot  Mesh 

Area  of  Mesh 

Square 
Centimeter. 

Square 
Inch. 

In  Milli- 
meters. 

In  Inches. 

0.0052 
0.0026 
0.0013 
0.00008 

In  Milli- 
meters. 

In  Inches. 

In  Square 
Millimeters. 

In  Square 
Inches 

900 
3,600 
15,000 
60,000 

4,200 
23.500 
97,000 
390,000 

*    0.133 
0.067 
0.033 
0.002 

0.20 
0.10 
0.05 
0.02 

0.0080 
0.0040 
0.0020 
0.0008 

0.04 
0.01 

0.0025 
0.0004 

0.0000610 
0.0000150 
0.0000040 
0.0000006 

The  relation  between  the  largest  diameter  of  particle  and  the  rate  of 
upward  flow  for  absolute  alcohol  and  Portland  cement  he  finds  to  be 

d  =  0.036/1, 

where  d  =  largest  diameter  in  millimeters,  and  v  =  upward  velocity  of  flow 
in  millimeters  per  second  in  the  cylindrical  part  of  the  washing  apparatus. 

As  a  result  of  this  further  analysis  for  fineness  it  appears  that  the  conclu- 
sions drawn  from  an  analysis  with  the  No.  75  and  the  No.  175  sieve  (30  and 
70  per  centimeter)  may  be  entirely  erroneous.  Thus  among  the  many 
analyses  given  by  Michaelis  in  these  articles  are  the  following  two  analyses 
of  cement  ground  in  the  same  manner,  on  French  buhrstones,  5  ft.  in 
diameter: 


Sieve-gauges  (Meshes  per  Linear  Inch), 
Wire  =  Width  of  Mes 

where  Diameter  of 
h. 

Sample  No.  1. 

Sample  No.  2. 

Parts. 

Total 
Passing. 

Parts. 

1.55* 

7.40 
19.74 
25.27 
46.04 

Total 

Passing. 

98.45^ 
91.05 
71.31 
46.04 

Retained  on  No   75  sieve 

0.65^ 
7.75 
42.98 
17.75' 

3087 

99.  35* 
91.60 
48  62 
30.87 

Passed  No.  75  and  retained  011  No. 
"  175    "           "          "     " 
"  300    "           "          "     " 
"       "  600  sieve  

175  sieve  
300  "  
600 

100.00 

100.00 

*  Thonindustrie-Zeitung  (Clay-industry  Gazette],  Berlin,  Aug.  24   and  Nov.  23,  1895.. 
Dr.  Michaelis  first  introduced  the  No.  175  sieve  in  Germany  about  1875. 


TESTING   OF  CEMENT. 


413 


41 


The  total  percentage  passing  the  No.  175  sieve  was  91.  GO  for  sample  No. 
1,  and  91.05  for  sample  No.  2.  This  would  appear  to  give  No.  1  a  slight 
advantage.  There  was  stopped  at  the  next  stage,  however,  43  per  cent  of 
No.  1  and  only  20  per  cent  of  No.  2,  thus  leaving  only  48. G2  per  cent  of 
No.  1  to  pass  the  300  sieve,  while  of  No.  2  there  passed  71.31  per  cent. 
Finally,  there  was  but  31  per  cent  of  No.  1  to  pass  the  washing  test  which 
corresponded  to  a  No.  600  sieve,  while  46  per  cent  of  No.  2  passed  this  last 
test  of  fineness.  It  thus  appears  that  sample  No. 
2  is  much  finer  ground  than  No.  1,  although  this 
would  not  appear  from  the  most  severe  sieve-test 
it  is  possible  to  make,  it  being  impracticable  to  use 
any  finer  sieve  than  about  175  meshes  per  linear 
inch  (70  per  centimeter). 

Mr.  Michaelis  strongly  urges,  therefore,  that 
in  all  scientific  and  expert  investigations  of  fine- 
ness the  washing  test  be  employed. 

311.  The  Thoroughness  of  the  Burning  is 
indicated  by  the  specific  gravity  of  the  ground 
cement.  If  the  cement  is  underburned,  it  is  rel- 
atively light.  This  test  is,  therefore,  really  a 
test  for  specific  gravity. 

Since  the  volume  of  a  given  weight  of  cement 
depends  altogether  on  the  way  in  which  it  is 
shaken  down  or  compacted,  it  is  impracticable  to 
determine  specific  gravity  by  weighing  measured 
volumes.  The  specific  gravity  of  cement  is  found, 
therefore,  by  means  of  an  apparatus  like  that 
shown  in  Fig.  332.  This  vessel  is  filled  with 
benzine  or  turpentine,*  up  to  the  zero  gradua- 
tion on  the  inserted  tube  or  above.  A  definite 
weight  of  cement  is  slowly  dropped  into  the  top 
of  this  tube,  care  being  taken  to  allow  all  air- 
bubbles  to  escape,  when  the  rise  of  the  liquid  in 
the  tube  will  indicate  the  true  volume  of  the 
cement  which  has  been  added.  If  metric  units 
have  been  used,  then  the  specific  gravity  of  the  FIG.  832.-Apparatus  for  De- 
cement  is  equal  to  the  weight  of  the  quantity  termining  the  Specific  Grav- 
added  in  grams  divided  by  the  increase  of  volume  ity  of  Cemeut,  as  used  by 
in  cubic  centimeters.  Since  well-burned  Port-  the  Author.  One-third 
land  cement  has  a  specific  gravity  of  more  than  natural  size. 


*  While  the  cement  has  no  tendency  to  set  or  harden  when  turpentine  is  used,  yet 
the  volume  of  this  liquid  is  so  sensitive  to  changes  in  temperature  that  it  is  not  advisable 
to  use  it  unless  the  cement,  the  turpentine,  and  the  vessel  all  have  the  temperature  of  the 
room,  and  this  latter  remains  constant  during  the  test. 


414 


THE  MATERIALS  OF  CONSTRUCTION. 


3.05,  this  figure  may  be  taken  as  a  minimum  specific  gravity  to  be  used 
in  a  specification. 

In  making  this  test  it  is  necessary  to  see  that  all  lumps  are  thoroughly 


T/ME  BEFOffE  SE77/NG  IS  COMPLETED 


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3  4    3    6    7    8    9   /O  //    /2  /3  /4  /5  /6  /7  /8  /9  20  2t  22  23  24  25  26  27  28  29  30  31  323334  35363738H) 

FIG.  333. — Graphical  Representation  of  the  Rate  of  Setting  of  Portland  Cement  at 
Various  Temperatures,  automatically  recorded  by  the  Apparatus  shown  in  Fig.  334. 
(Tetmajer.) 

pulverized  and  dried.     To  insure  this  it  should  be  passed  through  about  a 
No.  80  sieve,  that  remaining  on  the  sieve  to  be  added  to  the  specimen.     This 


45 


25 


/5 


X 


m 


&.    /4     tf     /8     20    22 

FIG.  333a. — Increase  in  Temperature  at  the  Centre  of  a  Heavy  Mass  of  Portland  cement 
Concrete  11.5  ft.  thick,  as  a  result  of  CheiuicaV  Action.  (Hep.  Fr.  Com.,  vol.  iv, 
PI.  III.) 

test  should  be  accurate  within  one  per  cent,  or  to  within  three  in  the  second 

decimal  place. 


TESTING   OF  CEMENT.  415 

This  test  is  not  usually  applied  to  natural  cements,  since  it  is  not  supposed 
that  they  will  be  burned  either  so  carefully  or  at  so  high  a  temperature  as 
is  required  for  Portland  cement. 

312.  The  Rate  of  Setting. — In  the  process  of  hardening  of  cement-mortar 
there  are  two  well-defined  stages,  known  respectively  as  the  beginning  and 
the  ending  of  the  setting.  A  quick-setting  Cement  may  begin  to  set  within 
a  very  few  minutes  after  wetting,  while  a  slow-setting  cement  may  require 


FIG.  834 — The  Amsler-Laffou  Apparatus  for  Automatically  Registering  the  Rate  of 
Setting  of  Cements  as  given  in  Fig.  333. 

more  than  twenty-four  hours  before  it  begins  to  set.  Usually  the  setting 
progresses  rapidly  after  it  has  begun,  as  indicated  in  the  curves  in  Fig.  333. 
These  curves  have  been  automatically  recorded  *  by  the  apparatus  shown  in 
Fig.  334.  This  setting  action  is  always  accompanied  by  a  slight  rise  in 
temperature.  In  fact,  with  quick-setting  cements  the  temperature  curve 
is  a  truer  index  of  the  setting  period  than  the  mechanical  tests  of  firmness 
which  are  usually  employed  for  this  purpose.  As  long  as  the  temperature 


*  Taken  from  Prof.  Tetmajer's  Reports,  vol.  vi. 


416 


THE  MATERIALS  OF  CONSTRUCTION. 


continues  to  rise  the  setting  action  is  in  progress,  and  the  rate  of  setting  is 
well  indicated  by  the  rate  of  increase  of  temperature. 

An  excellent  illustration  of  the  evolution  of  heat  by  chemical  action  in 
the  hardening  of  cement  is  furnished  by  Fig.  333«.  Here  the  rise  in  tem- 
perature was  observed  for  sixteen  days  at  the  centre  of  a  mass  of  Portland- 
cement  concrete  11.5  feet  thick.  The  temperature  rose  47. 5°  C.  (85.5°  F.) 
in  four  days,  and  reached  its  maximum  increase  of  52°  0.  in  seven  days,  after 
which  it  fell  off  very  slowly.  Both  the  temperature-curve  and  the  harden- 
ing-curve  are  automatically  recorded  by  the  apparatus  shown  in  Fig.  334. 
This  apparatus  was  manufactured  by  Messrs.  J.  Amsler-Laft'on  &  Son, 

Schaifhausen,  Switzerland.  Its  operation  is  too 
complex  to  be  explained  here.  It  is  in  satis- 
factory use,  however,  in  Prof.  Tetmajer's  labora- 
tory at  Zurich.  With  slow-setting  cements  the 
rise  of  temperature  cannot  be  observed  with 
accuracy,  and  is  smaller  in  amount  than  in.  the 
case  of  quick-setting  cements.  In  such  cases 
the  heat  developed  is  dissipated  because  of  its 
slow  generation,  and  does,  therefore,  not  be- 
come sensible  to  thermometric  measurement. 

The  usual  method  of  determining  the  set- 
ting period  is  by  means  of  such  an  apparatus 
as  shown  in  Fig.  335.  By  this  means  a  needle 
of  a  particular  diameter  and  loaded  with  a 

specified  weight  is  allowed  to  rest  upon  the 
cake  of  moYt^  which  for  thig  tegt  ghould  be 

mixed  neat,  and  the  setting  is  determined  by 
the  depth  of  penetration  of  the  needle.  When  the  needle  ceases  to  reach 
the  bottom  of  the  cake,  setting  is  supposed  to  have  begun;  and  when  it 
rests  wholly  on  the  top,  the  setting  is  supposed  to  have  been  completed. 
The  temperature-curve,  however,  indicates  a  continuation  of  this  action  for 
some  time  after  the  needle  ceases  to  penetrate  the  mass.  The  method 
commonly  employed  in  America  is  that  recommended  by  the  American 
Society  of  Civil  Engineers,  which  is  as  follows: 

A  neat  cement-mortar  having  a  stiff,  plastic  consistency  is  placed  in  a  form  two 
or  three  inches  in  diameter  and  one-half  inch  thick.  When  a  needle  one-twelfth 
inch  in  diameter,  weighted  with  one-fourth  pound,  ceases  to  penetrate  the  entire 
mass,  setting  is  said  to  have  begun  ;  when  a  needle  one  twenty-fourth  inch  in  diam- 
eter, carrying  one  pound,  will  not  penetrate  the  mass  at  all,  setting  is  said  to  have 
been  completed.* 

In  this  test,  those  cements  which  set  completely  in  one-half  hour  or  less 
are  known  as  quick-setting.  Those  requiring  much  more  time,  slow- setting. 
It  must  not  be  supposed  that  these  terms  are  used  rigidly  with  this  limit. 

*  The  French  Commission  recornmeud  a  needle  1.13  mm.  diameter  and  loaded 
with  300  grains  for  both  of  these  tests.  This  needle  is  0.045  inch  diameter  and  just 
1  suuare  millimeter  in  area.  The  load  is  11  ounces. 


FIG. 


335.  —  The    Vicat-needle 
Apparatus. 


TESTING   OF  CEMENT.  417 

In  Germany  and  France  a  needle  one  millimeter  in  diameter  is  loaded 
with  a  weight  of  300  grams,  and  the  beginning  and  the  end  of  the  setting 
period  is  indicated  by  the  time  when  this  needle  ceases  to  penetrate  the 
entire  mass,  and  when  it  ceases  to  penetrate  it  at  all,  respectively. 

The  time  when  the  setting  has  been  completed  can  be  approximately 
determined  by  efforts  to  indent  the  surface  with  the  finger-nail.  When  the 
surface  offers  some  appreciable  resistance  to  such  indentation,  the  cement 
may  be  said  to  have  set.  From  results  of  tests  given  in  Chapter  XXX  it 
does  not  seem  to  be  as  injurious  to  the  final  strength  of  the  mortar  to  use  it 
after  it  has  begun  to  set  as  it  has  commonly  been  supposed. 

313.  The  Test  for  Soundness. — This  is  a  test  of  the  permanency  of  vol- 
ume of  a  cement-mortar,  or  of  its  resistance  to  disintegrating   influences. 
Although  wrong  mixtures,  improper  calcining,  and  coarse   grinding   may 
lower  the  strength  of  a  cement,  a  strong  tendency  to  swell  or  to  disintegrate 
is  absolutely  fatal,  not  only  to  the  mortar,  but  also  to  the  structure  in  which 
it  is  used.     In  America  reliance  in  this  matter  has  been  placed  on  the  good 
record  of  the  particular  brand,  rather  than  on  actual  tests  to  determine  the 
"  soundness."      Professor   Tetrnajer  of  Zurich,  the  leading  authority  now 
on  cement-testing,  having  tried  various  methods  of  determining  this  prop- 
erty, recommends  for  Portland   cement  the    boiling  test  described  below. 
For  slag-cement  and  for  the  natural  cements  he  has  not  found  any  satisfac- 
tory means  of  determining  'this  quality  by  a  short  test. 

"While  "  soundness"  may  be  tested  by  a  long  maintenance  of  the  cement- 
cakes  under  water  and  in  the  air  for  many  years  at  least,  this  is  of  course 
not  possible  in  practice. 

It  is  true  that  all  cements  swell  under  water  and  shrink  in  the  air,  but 
these  changes  are  usually  inappreciable.  A  dangerous  swelling  of  volume 
under  water  may  be  caused  by  an  excess  of  quicklime  (CaO)  in  an  over- 
burnt  condition,  which  resists  the  slacking  action  of  water*  for  a  consider- 
able time.  These  cements  maybe  called  "lime-expanders." 

The  sulphur  compounds  of  lime  (CaS  and  CaS04,  or  gypsum)  may  cause 
the  cement  to  disintegrate  in  air  by  oxidation  and  the  absorption  of  water 
(becoming  CaS04+  2HOa  and  CaSO,  +  7HaO). 

If  magnesian  limestone,  or  dolomite,  forms  a  considerable  portion  of  the 
raw  ingredients,  after  years  of  apparent  soundness,  the  cement  may  disin- 
tegrate from  swelling,  if  under  water,  due  to  the  final  slacking  of  the  mag- 
nesia. Professor  Tetmajer  states,  however,  that  he  has  never  met  with  any 
actual  Portland  cement  which  has  failed  in  a  test  from  the  presence  of  the 
sulphur  or  the  magnesia  compounds.  It  seems,  therefore,  that  the  only 
source  of  nnsoundness  to  be  anticipated  is  an  excess  of  quicklime,  and  this 
is  best  determined  by  the  boiling  test. 

314.  The  Boiling  Test. — This  test  has  been  practised  for  the  past  twenty- 
five  years,  and  has  received  almost  universal  sanction.     At  the  Fifth  Inter- 
national   Convention    for   Unifying    Methods   for    Testing    Construction 


418 


THE  MATERIALS  OF  CONSTRUCTION. 


Materials,  held  in  Zurich,  Sept.  1895,  the  following  rules  for  conducting 
this  test  were  recommended  by  a  committee  of  the  leading  experts  of 
Europe,  Dr.  Michaelis  being  chairman,  who  originally  proposed  this  test 
about  1870. 

I.  The  rapid  test  of  hydraulic  cements  for  constancy  of  volume  consists  in  the 
application  of  warm  baths  at  temperatures  of  from  50°  to  100°  C.  (122°  to   212°  F.). 

II.  Manner  of  Making  the  Test-pieces. — Enough  water  is  used  to  bring  the  neat 
cement,  after   proper  working,  into  a  plastic  state.     Two  balls  from  40  to   50  milli- 
meters (1.5  to  2  inches)  in  diameter  are  formed  by  hand  and  kept  in  moist  air,  resting 
on  some  nonabsorbent  material.     (Sand  mixtures  are  not  to  be  subjected  to  this  test, 
neither  are  briquettes  which  are  to  be  tested  for  strength  to  be  so  treated.) 

The  employment  of  tension  briquettes  and  cylindrical  disks  from  50  to  100  milli- 
meters (2  to  4  inches)  in  diameter  and  from  15  to  30  millimeters  (£  to  1|  inches)  in 
thickness  is  likewise  permitted. 

III.  Duration  of  Previous  Hardening. — Until  set  has  taken  place  test-pieces  must 
be   kept  in  moist  air.      Portland,    slag,  Pozzuolana,    and  Roman   cements  will  be 
uniformly  kept  thus  for  twenty-four  hours;   very  slow-setting  ones  for  forty-eight 
hours.     Hydraulic  limes  and  all  cements  that  have  not  completely  set  after  forty- 
eight  hours  will  be  allowed  seventy-two  hours  for  previous  hardening. 

IV.  Treatment  in  the  Warm  Bath. — The  previously  hardened   test-samples  are 
placed   in  a  water-bath  at  ordinary  temperature,  which  is  then  gradually — not  in 
less  than  thirty  minutes — heated  to  the   prescribed  temperature  and  kept  there. 
After  three  hours  at  the  prescribed  temperature  the  test  is  interrupted,  the  test- 
pieces  are  taken  out  of  the  bath,  and  after  having  cooled  sufficiently,  examined  as 
to  their  condition.     They  must  not  be  chilled  suddenly  by  means  of  cold  water. 

For  each  warm-bath  test  the  water  must  be  renewed.  The  temperature  of  the  bath 
will  be: 

For  Roman  cements  and  hydraulic  limes,  50°  C.  (122°  F.);  for  Portland  slag  and 
Pozzuolana  cements,  100°  C.  (212°  F.). 

V.  In  order  to  be  considered  of  absolutely  constant  volume  the  test-sample  must, 
during  this  test,  remain  perfectly  sound  and  entirely  free  from  cracks  and  warping. 


FIG.  336. — Showing  Methods  of  Failure  of  Cements  under  the  Boiling  Test.* 

If  the  ball  cracks  slightly  in  this  test  or  disintegrates  somewhat  as  shown 
in  Fig.  33G,  it  should  be  considered  at  least  doubtful,  although  it  might 
not  fail  in  actual  practice. 

A  modification  of  this  test  is  to  maintain  a  bath  at  a  little  less  than  the 
boiling  temperature,  in  order  to  prevent  the  wearing  action  of  the  boiling 
water.  As  it  is  difficult,  however,  to  maintain  such  a  temperature,  the  boil- 

*  These  cuts  are  taken  from  Professor  Tetmajer's  Communications  for  1893. 


TESTING   OF  CEMENT. 


419 


ing  test  is  to  be  preferred,  using  the  least  fire  which  will  maintain  this  tem- 
perature. At  the  end  of  this  three-hour  period  the  specimens  will  be  found 
to  be  extremely  hard  and  solid,  like  stone.  No  other  test  for  soundness  need 
be  employed.  This  test  is  to  be  employed  only  with  Portland  cements,  as 
probably  few  natural  cements  would  stand  it.  No  satisfactory  test  for  the 
soundness  of  natural  cements  has  been  found,  and  the  fact  that  these  cements, 
which  may  go  all  to  pieces  in  the  boiling  test,  still  stand  well  in  service  forms 
a  strong  argument  against  the  drawing  of  adverse  conclusions  from  this  test 
when  applied  to  Portland  cements.  The  question  of  what  tests  to  apply  to 
determine  the  weathering  qualities  of  cements  is  as  yet  unsolved. 

TESTING  THE  STRENGTH  OF  CEMENT. 

315.  Tensile  Test  Sufficient. — Although  cement-mortar  and  concrete  are 
commonly  subjected  to  a  compressive  stress  only,  and  hence  the  strength  in 
compression  is  of  the  greatest  importance,  the  only  test  of  strength  usually 


8 


FIG.  337.— Showing  the  Ratio  of  the  Tensile  to  the  Compressive  Strength  of  Portland  - 
cement  Mortar,  1  C. :  3  S.,  by  Weight.  Each  point  plotted  is  the  average  of  550  tests  of 
each  kind.  Equation  of  curve,  R=  8.64  -f  1.8  log  A.  (Data  taken  from  Tetmajer's 
Communications,  vol.  vi.) 

made  is  that  in  tension.  In  Art.  20  it  was  shown  that  the  strength  of  such 
materials  in  compression  is  really  their  strength  in  shearing,  and  for  a  gran- 
ular material  the  strength  in  shearing  would  be  expected  to  vary  with  the 
strength  in  tension.  It  was  to  be  presumed,  therefore,  that  the  tensile 
strength  of  cement  would  have  a  definite  relation  to  its  compressive  strength. 
The  author  is  now  able  to  establish  this  relation  as  shown  in  Fig.  337. 
Here  55  samples  of  Portland-cement  mortar,  one  of  cement  to  three  of 
sand,  by  weight,  were  tested  by  Professor  Tetmajer  both  in  tension  and  in 


420  THE  MATERIALS  OF  CONSTRUCTION. 

compression,  there  being-  fifty  tests  of  each  kind  from  each  sample.  One 
third  of  these  were  left  to  harden  in  air,  and  two  thirds  hardened  under 
water.  These  fifty  tension-  and  fifty  compression-test  specimens  of  each 
mixture  were  divided  into  five  lots  of  ten  each,  and  these  were  tested  in  five 
periods  of  time,  namely,  in  7  days,  28  days,  8-4  days,  210  days,  and  1  year. 
The  average  ratios  of  the  compressive  to  the  tensile  strength  of  the  550  tests 
of  each  kind  made  at  each  of  the  above  periods  are  plotted  in  Fig.  337,  and 
joined  by  the  full  line.  The  probable  error  of  each  of  these  ratios  was  also 
determined  from  the  residuals  obtained  by  comparing  each  of  the  fifty-five 
results  with  its  average,  and  these  probable  error-limits  are  also  indicated  in 
the  diagram.  These  limits  are  so  uniform  and  so  small  as  to  lead  to  the 
necessary  conclusion  that  the  ratio  between  the  compressive  and  the  tensile 
strength  of  cement  is  a  very  rigid  one  for  any  given  age,  but  that  it  increases 
with  the  age  of  the  mortar.  This  curve  is  very  nearly  represented  by  the 
following  equation,  the  maximum  deviation  of  which  from  the  observed  locus 
is  less  than  one  half  of  one  per  cent 

Compr.  strength 

Eatio  :  ril      \.  .-  =  8.64  -J-  1.8  log  A, 

Tensile  strength 

where  A  =  age  of  the  cement-mortar  in  months.  The  compression  tests  were 
made  upon  cubical  forms.  The  value  of  this  study  is  not  so  much  the 
determination  of  the  true  relation  between  the  tensile  and  the  compressive 
strength  of  cement-mortar  as  it  is  to  show  that  the  tensile  test  is  sufficient 
to  determine  compressive  strength.* 

316.  Standard  Consistency  of  Neat-cement  Test-specimens. —It  has  been 
found  impracticable  to  specify  any  particular  percentage  of  water  for  all 
kinds  of  cement,  or  even  for  all  brands  of  one  class,  as  of  Portland 
cement,  or  of  natural  cement,  or  of  slag-cement.  A  certain  consistency  of 
the  gauged  cement  demands  various  percentages  of  water  with  different 
brands  of  the  same  class  of  cements.  It  is  necessary,  therefore,  to  have  a 
standard  method  of  fixing  this  consistency.  The  effect  of  using  varying 
quantities  of  water  with  a  single  brand  of  cement  is  shown  in  Figs.  338  to 
343.  When  an  excess  of  water  is  used  the  briquettes  are  greatly  weakened 
for  short  periods,  but  the  effect  partly  disappears  with  time.  When  too 
small  a  quantity  of  water  is  used,  it  requires  too  much  work  to  thoroughly 
compact  the  briquettes,  and  the  results  are  apt  to  be  irregular. 

The  French  Commission  have  .adopted  a  modified  form  of  Prof.  Tet- 
majer's  method  of  determining  consistency,  which  is  as  follows: 

(1)  Take  one  kilogram  (2  Ibs.  5  oz.)  of  cement,  place  it  on  a  marble  slab, 
arrange  it  in  a  crater-like  form,  and  add  at  one  pouring  all  the  water  which  is  to  be 

*  M.  Feret  has  shown  in  An.  d.  Fonts  et  Ckaussees,  7th  series,  vol.  iv.  p.  1,  Fig.  19 
(1896),  that  this  ratio  becomes  greater  for  higher  proportions  of  sand.  In  fact  the  com- 
pressive strength  varies  uniformly  with  the  proportion  of  cement  used,  while  the  tensile 
strength  is  nearly  constant  for  small  proportions  of  sand  but  falls  rapidly  for  the  poorer 
mixtures. 


TESTING   OF  CEMENT. 


421 


28 


FIG.  338.  —  Effect  of  Varying  Percentages  of  Water  used  in  Gauging  Portland-cement 
Mortar,  1  C.  :  3  S.  Average  results  on  five  brands  of  cement.  Each  point  plotted 
is  the  mean  of  fifty  tests.  (Tetmajer,  vol.  vn,  1894,  p.  10.) 


600 


400 


200 


22  26          <30 

FIG.  339.— Effect  of  Varying  Percentages  of  Water  in  Gauging  Neat  Portland  Cement. 
(Jour.  West.  Soc.  Engrs.,  vol.  i.  p.  82,  Table  XVIII.) 


422 


THE  MATERIALS  OF  CONSTRUCTION. 


^> 


& 


?7/?l 


I 


FIG.  340.— Tensile  Strength  of  Natural  Cement-mortars,  mixed  with  Different  Percent- 
ages of  Water.     (Wheeler,  Rep.  Ckf.  Engrs.,  U.  S.  A.,  1894,  p.  2332.) 


TESTING   OF  CEMENT. 
26  3O  3S 


423 


430 


2OO 


/OO 


PERCENTAGE          QF        WATER 

FIG.  341. — Effect  of  Varying  Percentages  of  Water  on  Time  of  Setting  of  Xeat  Cement. 
(Wheeler,  Rep.  Clif.  Engrs.,  1895,  p.  2935.) 


24  28  <32  <3G  40 

FIG.  342. — Effect  on  the  Strength  of  Louisville  (Natural)  Cement,  Neat,  of  a  Varying 
Percent  of  Water  in  Gauging.     (Jour.  West.  Soc.  Engrs.,  vol.  i.  p.  82,  Table  XVI.) 

used,  this  volume  being  that  necessary  to  satisfy  the  conditions  described  in  (2). 
The  water  to  be  either  fresh  or  salt,  as  may  be  specified.  The  whole  is  then  stirred 
and  turned  rapidly  with  a  trowel  for  five  minutes,  counting  from  the  instant  the 
water  was  added. 

(2)  With  a  portion  of  this  gauged  cement  fill  a  vessel  having  an  interior  form  of 
a  truncated  cone,  8  cm.  (3J  inches)  in  diameter  at  bottom,  9  cm.  (3f  inches)  in 
diameter  at  top,  and  4  cm.  (If  inches)  deep,  smoothing  it  off  quickly  on  top  with 
the  trowel. 

Upon  the  centre  of  this  top  surface  bring  to  bear  normally  and  slowly  a  cylinder 
of  polished  metal  1  cm.  (f  inch)  diameter  and  weighing  0.3  kilogram  (11  oz.),  having 
a  full,  flat,  transverse  sectional  base.  The  apparatus  to  be  constructed  so  as  to 


424 


TEE  MATERIALS  OF  CONSTRUCTION. 


indicate  the  thickness  of  the  film  of  mortar  remaining  below  the  cylinder  when  it 
ceases  to  settle  under  its  own  weight.  Two  tests  to  be  made  on  the  same  cake. 

The  consistency  to  be  considered  as  normal  when  the  cylinder  stops  just  J  inch 
from  the  bottom  of  the  cake. 

For  quick-setting  cements  use  one  half  the  amount  of  dry  cement,  and  mix  one 
minute  instead  of  five. 


FIG.  343. — Effect  of  Varying  Percentages  of  Water  iu  Gaugiug  Utica  (Natural) Cement- 
mortar,  1  C.  :  1  S.     (Jour.  West.  Soc.  Engrs.,  vol.  I.  p.  82,  Table  XV.) 

317.  Normal  or  Standard  Sand. — That  the  quality  of  the  sand  exerts  a 
marked  influence  on  the  strength  of  cement-mortar  is  shown  by  Figs.  344 
and  345.  These  tests  show  the  great  superiority  of  calcareous  over  siliceous 


FIG.  344.— Effect  of  the  Quality  of  the  Sand  on  Strength  of  Cement-mortar,  1  C.:  3  S. 
(Wheeler,  Rep.  Chf.  Engrs.,  U.  S.  A.,  1894,  vol.  iv.  p.  2321.) 

sands  in  giving  strength  to  the  mortar.     Evidently,  however,  sands  con- 
taining small  shells  containing  air-spaces  should  be  excluded. 

To  find  the  composition  of  a  sand  immerse  it  in  cold  hydrochloric  acid, 
which  will  dissolve  the  siliceous  portion.  The  residuum  may  then  be  sepa- 
rated into  the  insoluble  calcareous  sand  and  the  clay,  by  rubbing  and  wash- 


TESTING   OF  CEMENT. 


425 


ing,  and  thus  its  three  significant  constituents  determined  with  sufficient 
accuracy  for  commercial  purposes. 

Not  only  the  strength  but  the  permeability  of  mortar  depends  on  the 
size  of  the  sand-grains;  and  as  the  resistance  to  the  decomposing  action  of 


800 


700 


£00 


£00 


FIG.  345. — Comparative    Value    of   Different    Sands  in    Portland-cement   Mortar    18 
months  old  (in  water).     (Wheeler,  Rep.  Chf.  Engrs.,  1895,  vol.  iv.  p.  2953.) 

frost  and  sea-water  depends  almost  wholly  on  its  impermeability,  the  life 
of  the  mortar,  in  exposed  situations,  is  largely  dependent  on  the  character 
of  the  sand  used. 

In  order  that  tests  of  the  strength  may  be  comparable,  therefore,  it  is 
necessary  to  choose  a  normal,  or  standard,  sand.  In  Germany  and  in  France 
natural  sands  are  chosen,  while  in  the  United  States  a  committee  of  the 
American  Society  of  Civil  Engineers  recommended  in  1885  the  use  of 
crushed  quartz,  such  as  is  used  in  making  sand-paper,  of  a  size  which  passes 
a  No.  20  sieve  and  is  stopped  on  a  No.  30  sieve.  This  leaves  all  the  grains 
with  maximum  dimensions  of  from  1  mm.  to  1.5  mm.  When  the  grains  are 
so  nearly  of  the  same  size  and  very  angular  or  "splintery"  the  proportion 
of  voids  is  very  great,  so  that  a  mixture  of  1  cement  to  3  sand  by  weight  will 
not  be  solid  without  a  great  amount  of  pounding  on  the  briquette,  which 
must  be  mixed  dry  to  enable  it  to  receive  such  treatment. 


426  THE  MATERIALS  OF  CONSTRUCTION. 

225 


2OO 


/SO 

7  /4  2J  28 

FIG.    346.— Comparative  Value    of  Three  Kinds  of  Sand  for  Portland- cement  Mortar, 
1  0. :  3  S.     (St.  Louis  Water  Dept.,  1895.) 


300 


20-4O 


/MSSEO/0 

FIG.  347. — Effect  .of  Fineness  of  Sand  on  Strength  of  Portland-cement  Mortar,  1  : 1  and 
1 :  2.     Age  6  months.     (Wheeler,  Rep.  Clif.  Engrs.,  1895,  p.  2972.) 


TESTING   OF  CEMENT. 


427 


The  French  Commission  have  adopted  the  following: 


Normal  or  standard  sand  consists  of  sand  found  on  the  beach  at  Leucate,  and  is 
of  three  sizes: 

No.  1,  passing  a  sieve  of  1  mm.  and  retained  on  one  of  0.5  mm.  mesh. 
No.  2,  passing  a  sieve  of  1.5  mm.  and  retained  on  one  of  1  mm.  mesh. 
No.  3,  passing  a  sieve  of  2  mm.  and  retained  on  one  of  1.5  mm.  mesh. 

Simple  normal  sand  is  construed  as  meaning  No.  2.  Composite  or 
mixed  normal  sand  is  construed  as  meaning  all  three  sizes  in  equal  parts, 
this  mixture  approaching  closely  the  sand  ordinarily  employed  in  engineer- 
ing works.  The  finest  grade,  No.  1,  corresponds  to  such  fine  sand  as  is 
found  in  the  sand-dunes  along  our  sea  and  lake  shores,  while  the  coarsest, 
No.  3,  corresponds  to  the  very  coarse  sand  taken  from  the  bed  of  a  rapidly- 
flowing  river.  The  composite  or  mixed  sand  is  exclusively  used  in  standard 
tests  of  mortar.  This  is  to  be  commended,  as  it  gives  fewer  voids,  and  a 
mixture  of  1  cement  to  3  sand  readily  makes  a  perfectly  solid  test  specimen. 
The  above  sieves,  having  meshes  of  0.5,  1.0,  1.5,  and  2  millimeters,  would  be 
found  to  have  approximately  35,  20, 15,  and  11  meshes  per  inch  respectively. 


FIG.  348. — Showing  Effect  of  Varying  Fineness  of  Clean  River-sand  in  Cement-mortar, 
1  C.  :  3  S.     (Wheeler,  Rep.  Chf.  Engrs.,  vol.  iv,  1894.) 


In  place,  therefore,  of  using  a  20-30  sand  in  making  up  standard  mortar- 
test  specimens,  as  has  become  customary  in  America,  in  accordance  with 
the  American  Society  of  Civil  Engineers  Committee's  recommendation,  the 
French  are  using  a  sand  composed  equally  of  three  grades,  which  are  respec- 
tively 11-15,  15-20,  and  20-30  sieve  samples.  This  gives  sand-grains  vary- 
ing from  0.5  mm.  to  2.0  mm.  in  size,  or  a  variation  in  size  of  300$  of  the 
smallest,  while  the  American  Society  of  Civil  Engineers'  standard  allows 


428 


THE  MATERIALS  OF  CONSTRUCTION. 


&  S0  &  £0  25 

FIG.  349.— Effect  of  Size  of  Limestone  Screenings  when  used  as  Sand  in  Portland- 
cement  Mortar,  1  C.  :  3  S.     (Wheeler,  Rep.  Chf.  Engrs.,  1894,  vol.  iv.) 


/<?  X?  20  25 

FIG.  350, — Variation  in  Volume  of  Different  Grades  of  Sand  by  the  addition  of  small 
quantities  of  water.    (Wheeler,  Rep.  Chf.  Engrs.,  1895,  p.  2935.) 


TESTING   OF  CEMENT.  429 

but  50$  variation  in  the  size  of  the  sand-grains  for  the  standard  mortar- 
tests. 

318.  Standard  Consistency  of  Cement-mortars. — The  standard  cement- 
mortar  is  composed  of  one  part  of  cement  to  three  parts  of  standard  sand, 
by  weight.  The  great  variation  in  volume  of  sand  with  varying  percentages 
of  water,  as  shown  by  Fig.  350,  precludes  the  volume  measurement  even  of 
the  sand,  while  with  the  cement  there  is  no  fixed  relation  between  volume 
and  weight.  It  has  been  customary  for  many  years  in  Germany  to  use  the 
minimum  amount  of  water  which  would  enable  this  mixture  to  be  com- 
pacted in  a  briquette  by  the  action  of  what  is  known  as  Bohme's  hammer 
(see  Fig.  352),  in  the  use  of  which  150  blows  is  given  to  each  briquette.  As 
this  is  a  condition  very  far  removed  from  those  of  actual  practice,  it  has 
always  been  objected  to  in  other  countries,  and  has  never  come  to  be  stand- 
ard in  America.  When  a  greater  quantity  of  water  is  used,  however,  so  as 
to  give  a  plastic  mortar,  it  cannot  be  compacted  by  pounding  and  it  becomes 
more  difficult  to  obtain  uniform  results.  The  French  Commission  have 
studied  this  question  most  effectually,  and,  while  they  are  forced  to  still 
recognize  the  dry  mixture  as  above  described,  they  strongly  recommend 
the  use  of  plastic  mortars,  and  express  the  hope  that  the  German  standard 
method  of  preparing  these  specimens  will  fall  into  disuse.  Their  recom- 
mendations on  this  subject  are  as  follows: 

1.  Standard  plastic  cement-mortar  shall  be  composed  of  one  part  of  cenient  (250 
grams)  to  three  parts  of  mixed  normal  sand  (750  grams),  this  being  composed  of 
equal  parts  of  numbers  1,  2,  and  3,  as  described  in  Art.  317.     These  will  be  mixed 
thoroughly  before  water  is  added,  on  a  marble  slab,  and  then  ganged  with  the  full 
quantity  of  water,  either  fresh  or  salt  as  the  case  may  be,  and  vigorously  stirred  and 
worked  for  five  minutes. 

The  quantity  of  water  to  be  used  to  be  such  that  when  the  vessel  described  in 
Art.  316  is  filled  with  the  mortar  and  smoothed  off,  a  fewr  strokes  of  the  trowel  upon 
the  sides  of  this  vessel  will  cause  the  mortar  to  liquefy  slightly  at  the  surface. 

For  cements  which  set  rapidly  the  total  quantity  of  materials  u^ed  to  be  reduced 
to  500  grams,  and  the  gauging  to  be  continued  for  one  minute  instead  of  five. 

2.  Standard  dry-cement  mortars  shall  be  composed  of  one  part  of  cement  (250 
grams)  to  three  parts  (750  grams)  of  standard  sand  No.  2  (described  in  Art.  316), 
these  to  be  mixed  while  dry  on  a  marble  slab,  and  then  an  amount  of  water  added 
equal  to  one  sixth  of  that  necessary  to. use  in  bringing  one  kilogram  of  the  same 
kind  of  neat  cement  to  the  standard  consistency  described  in  Art.  316  plus  45  grains 
additional.* 

3.  If  other  proportions  are  desired  than  one  of  cement  to  three  of  sand,  it  is 
recommended  that  one  of  cement  to  two  of  mixed  standard  sand,  and  one  of  cement 
to  five  of  mixed  standard  sand,  be  used  ;  these  also  to  be  regarded  as  standard,  rich, 
and  poor  mortar,  respectively.     The  amount  of  water  to  be  used  in  each  case  to  be 
such  as  to  produce  a  plastic  mortar  which  will  satisfy  the  conditions  named  above  in  1. 

*  For  the  standard  dry  mortars  of  varying  proportions  of  sand,  and  for  all  kinds  of 
cement,  the  amount  of  water  to  use  was  found  to  be,  in  grams  for  1  kg.  of  the  dry 
mixture,  w  =  %WC-{-  45,  where  W  =  weight  of  water  in  grams  required  to  bring  1  kg. 
of  the  pure  cement  to  the  normal  consistency  described  in  Art.  316,  and  C  =  weight  m 
kilograms  of  the  cemeut  entering  into  the  dry  mixture. 


430  THE  MATERIALS  OF  CONSTRUCTION. 

In  place  of  the  hand-mixing  on  a  slab,  as  described  above,  the  author  has 

•sised  with  very  satisfactory  results  the  Faija 
mechanical  mixer,  made  by  Eiehle  and  shown 
in  Fig.  351.  Something  of  this  sort  is  espe- 
cially helpful  in  the  case  of  sand  mixtures,  the 
sand  and  cement  being  first  mixed  dry  and 
then  from  three  to  five  minutes  after  wetting. 

The  St.  Louis  Water  Department  use  for 
neat  cement  a  "jig,"  consisting  of  a  pair  of 
cups  mounted  vertically  on  a  reciprocally  mov- 
ing head-piece,  operated  by  a  very  rapid  circular 
motion,  like  the  familiar  "  milk-shake  "  appa- 
ratus. (See  drawings  and  description  in  Engr. 
J\'ews,  vol.  xxv.  p.  3,  1891.) 

319.  The  Formation  of  the  Briquettes. — The  following  rules  for  forming 
the  briquette  are  based  largely  on  the  Eeport  of  the  French  Commission, 
but  they  also  fairly  represent  the  best  current  American  practice. 

A.   For  Standard  Plastic  Mortar,  1  Cement  to  3  Sand. 

(1)  The  briquette  to  be  of  the  form  shown  in  Fig.  355  or  Fig.  356, 
having  just  one  square  inch  of  minimum  cross-section.* 

(2)  The  moulds  to  be  quite  clean,  and  to  be  rubbed  with  an  oiled  or 
greased  linen  cloth,  and  placed  on  a  plain  marble  slab,  or  plate-glass,  or 
polished  metal  surface.     Six  moulds  to  be  simultaneously  filled  to  overflowing 
(if  the  cement  is  slow-setting,  and  but  four  moulds  to  be  filled  if  it  is  quick- 
setting),  the  entire  amount  required  for  one  mould  to  be  inserted  at  one 
time.     The  mortar  to  be  pressed  into  the  moulds  with  the  fingers,  and  a  few 
strokes-  given  to  the  side  of  the  mould  with  the  trowel.     This  having  been 
done  for  the  entire  set  (of  six  or  four  as  the  case  may  be),  the  excess  of 
mortar  is  carefully  removed  with  a  straight-edged  blade  resting  on  the  top 
edge  of  the  moulds,  but  without  exerting  any  compression  on  the  material 
below  this  plane.     The  surface  is  then  polished  off  with  the  trowel,  and  the 
whole  covered  with  wet  cloths,  and  kept  from  sun  and  wind,  in  a  saturated 
atmosphere,   and  at  a  temperature  of  from  60  to  70°  F.     When  making 
plastic  briquettes  of  neat  cement,  it  may  be  best  to  allow  them  to  stand  a 
•while  before  removing  the  excess  of  material  and  polishing  off. 

(3)  After  the  mortar  has  set   (at  the  end  of  24  hours,   or  sooner)   the 
mould  is  tapped  lightly  on  the  side  to  loosen  the  briquette  from  the  bed- 
plate, when  the  mould  is  unlocked  and  removed  from  around  the  briquette. 
These  are  not  raised  from  the  plate  (if  the  moulds  are  removed  inside  of  24 
hours),  but  are  covered  with  wet  cloths  until  24  hours  have  elapsed  from  the 
time  of  mixing  with  water. 

*  The  European  standard  section  is  5  sq.  cm.  or  0.8  sq.  in.  The  ordinary  American 
form  of  briquette  (Fig.  354)  should  be  abandoned  at  once,  since  it  is  impossible  to  pre- 
vent such  briquettes  of  neat  Portland  cement  from  breaking  in  the  clips. 


TESTING   OF  CEMENT.  431 

For  very  quick-setting  cements  the  time  period  in  air  for  neat  cement 
may  be  reduced  to  one  hour,  and  for  mortar  briquettes  to  three  hours. 

A  careful  weighing  of  the  briquettes  when  removed  from  the  moulds  gives 
a  very  good  check  on  the  uniformity  of  their  composition. 

(4)  At  the  expiration  of  the  period  described  in  (3)  the  briquettes  are 
placed  in  their  required  medium  till  tested.     If  they  are  placed  in  fresh 
water,  this  should  be  changed  as  often  as  once  a  week.    If  placed  in  sea- water, 
it  should  be  changed  every  two  days  for  the  first  week,  and  then  once  a 
week.     The  water-volume  should  be  at  least  four  times  that  of  the  briquettes 
immersed  in  it. 

If  the  briquettes  are  to  harden  in  air,  this  should  be  kept  near  the  point 
of  saturation,  and  they  should  be  protected  from  all  air-currents  and  from 
the  rays  of  the  sun.  The  temperature  of  the  medium,  whether  of  air  or 
water,  should  remain  from  60°  to  65°  F.  (15°  to  18°  C.). 

(5)  The  tensile  testing-machine  to  be  so  arranged  as  to  give  a  uniform 
imposition  of  the  load  at  the  rate  of  12  pounds  (5  kg.)  per  second.     The 
form  of  the  grips  to  be  that  shown  in  Fig.  3G3. 

(6)  Standard  tests  of  cement-mortar  to  be  made  at  the  end  of  7  days,  28 
days,  3  months,  6  months,  1  year,  and  2  years,  all  computed  from  the  time 
of  gauging.     For  mortar  made  from  quick-setting  cement  the  shortest  period 
to  be  2-i  hours,  and  for  quick-setting  neat  cement  briquettes  the  short  periods 
to  be  3  hours,  and  24  hours  from  the  time  of  gauging. 

(7)  So  far  as  possible  the  six  briquettes  made  from  a  given  gauging  to  be 
divided  uniformly  among  the  lots  to  be  tested  at  different  periods.     Thus  if 
tests  are  to  be  made  after  six  such  periods,  as  named  above,  then  one  briquette 
from  each  gauging  to  be  assigned  to  each  period. 

A  single  result  for  any  period  to  be  the  mean  of  the  tests  on  six  briquettes, 
defective  samples  to  be  rejected,  however,  and  the  mean  to  be  derived  from 
the  remaining  perfect  tests,  all  the  facts  to  be  indicated  on  the  record. 

The  results  to  be  given  as  so  many  pounds  per  square  inch  (kilograms 
per  square  centimeter)  tensile  strength  on  the  standard  form  of  briquette  of 
one  square  inch  (5  sq.  cm.  in  Europe)  in  cross-section. 

B.  For  Standard  Dry  Mortar,  1  Cement  to  3  Sand. 

(1)  All  the  conditions  specified  in  A  to  be  complied  with.     In  addition 
to  these  the  following  rules  will  be  observed : 

(2)  At  the  moment  of  mixing,  the  cement,  the  sand,  the  water,  and  the 
air  to  be  at  a  temperature  between  60°  and  65°  F.  (15°  to  18°  C.).     After 
the  moulds  are  filled  to  overflowing,  and  the  mortar  has  been  pressed  to  place 
with  the  fingers,  it  will  be  pounded  on  the  surface  with  a  heavy  spatula,  14 
inches  long  over  all,  including  the  handle,  and  having  a  surface  of  blade  of 

four  square  inches  (25  sq.  cm.)  and  weighing  9  ounces*  (250  gr.).     The 

. 

*  No  cut  of  this  is  given.  If  the  blade  itself  is  to  weigh  250  gr.,  it  would  be,  say, 
one  inch  wide,  one-half  inch  thick,  and  four  inches  long. 


432  THE  MATERIALS  OF  CONSTRUCTION. 

briquette  to  be  beaten  at  first  with  light  strokes  near  the  ends,  then  towards 
the  centre.  These  to  be  followed  by  heavier  strokes,  always  following  the 
same  course  over  the  surface  of  the  briquette,  and  continuing  this  treatment 
till  the  mass  becomes  somewhat  plastic  and  water  begins  to  appear  at  the 
surface.  The  surface  is  then  scraped  and  smoothed  off  as  before. 

For  many  years  standard  cement-mortar  briquettes  have  been  formed  in 
Germany  almost  exclusively  by  the  use  of  a  machine  shown  in  Fig.  352, 


FIG.  352.— Dr.  Bohme's  Hammer  for  making  Cement  Briquettes. 

which  is  the  invention  of  Prof.  Bohme  of  Charlottenburg.  The  hammer  is 
driven  by  a  wheel  with  ten  cams,  connected  by  simple  gearings  with  a  crank 
and  handle.  The  steel  hammer  weighs  four  and  one-half  pounds.  This 
apparatus  may  be  used  for  making  either  tension-  or  compression-test  speci- 
mens, and  is  preferably  used  when  these  are  made  of  standard  mortar  mixed 
dry.  There  is  an  automatic  stop  which  acts  at  the  end  of  150  strokes,  this 
being  the  usual  number  of  blows  given  to  eacli  test-specimen.  Fig.  353 
shows  an  apparatus  used  by  Prof,  von  Tetmajer  and  which  has  now  been 
recommended  for  general  use  to  the  Fifth  International  Convention  for 
Unifying  the  Methods  of  Testing  Engineering  Materials,  which  met  at 
Zurich  in  September  1895.  The  French  Commission  have  not  included 
either  of  these  kinds  of  apparatus  in  their  standard  specifications  given  above. 
320.  The  Form  of  the  Briquette.- — After  nearly  a  half-century  of  experi- 
menting on  a  great  many  different  forms  of  briquettes,  two  leading  forms  are 
now  used  to  the  practical  exclusion  of  all  others.  The  English  form  shown., 
in  Fig.  354,  having  a  minimum  section  of  one  square  inch,  is  used  in  England 
and  in  America,  and  the  German  form  shown  in  Fig.  355,  having  a  minimum 


TESTING   OF  CEMENT. 


433 


section  of  five  square  centimeters,  is  used  on  the  continent  of  Europe,  having 
recently  been  recommended  by  the  French  Commission. 

A  great  objection  to  the  English  standard  form  shown  in  Fig.  354  is  that 
a  very  large  proportion  of  briquettes  of  neat  cement  over  four  weeks  old 
(about  50  Der  cent)  break  in  the  clips  and  not  on  the  minimum  cross-section. 


FIG.  353.— Tetmajer's  Apparatus   for        FIG.  354. — Standard  Form  of  Briquette  used 
Compacting  Dry-mortar  Briquettes,  ill  England  and  America.     Full  size, 

with  an  adjustable  height  of  drop. 
(Fr.  Com.  Rep.,  vol.  i.  p.  287,  and 
also  Zurich  Laboratory  Communica- 
tions, vol.  vn.  p.  118.) 

This  is  partly  the  fault  of  the  small  bearing-surface  provided  in  the  form  o, 
clips  used,  but  it  is  also  largely  due  to  the  form  of  the  briquette.  The  angle 
which  the  two  bearing-surfaces  form  with  each  other  is  small,  and  the  com- 
pressive  stress  resulting  is  correspondingly  large,  so  that  the  briquette  is  apt 
to  fail  in  the  plane  of  the  bearings  from  a  combined  vertical  tension  and  a 
lateral  compressive  stress. 

The  conditions  which  should  be  fulfilled  in  the  form  of  a  cement 
briquette  for  tensile  tests  are : 

(1)  The  bearing-surfaces  in  the  clips  should  form  an  angle  with  each 
other  of  more  than  90°. 

(1}  The  minimum  section  should  be  removed  far  enough  from  the  plane 
of  the  bearings  in  the  clips  to  insure  a  nearly  even  distribution  of  stress  over 
this  minimum  section. 

(:>)  The  minimum  section  should  be  small  enough  to  insure  rupture  on 
this  portion  of  the  briquette,  but  the  reduction  should  be  by  gentle  curves. 

The  English  form  (Fig.  354)  is  very  defective  in  the  first  requirement,  as 


434 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG.  355. — The  European  Continental  Form  of  Briquette. 


__H_  - 


///  "      I  /  <?/  "  i?/ 

l^-;/^  -^--/^  -*-% 


FIG.  356  —  Form  of  Briquette  designed  by  the  Author.     Full  size. 


TESTING    OF  CEMENT. 


435 


this  angle  is  only  about  60°,  while  the  German  form  in  this  respect  is  excel- 
lent, its  angle  being  100°. 

Both  forms  are  defective  in  the  second  requirement,  as  they  are  shortened 
up  from  reasons  of  economy  and  convenience. 

The  German  form,  Fig.  355,  is  defective  as  to  the  third  requirement,  in 
that  the  reduction  of  section  is  too  sudden. 

The  author  has  devised  and  used  a  modification  of  the  German  form,  as 
shown  in  Fig.  35G,  and  he  finds  that  it  gives  over  twenty-five  per  cent  greater 
strength  than  the  English  form,  and  the  briquettes  never  break  in  the  clips 
he  uses  with  it,  shown  in  Fig.  3G3.  The  greater  strength  of  this  form 
results  from  the  more  even  distribution  of  stress  across  the  section  of  rupture, 
owing  to  the  farther  removal  of  the  bearing-surfaces  of  the  clips,  while  the 
large  angle  formed  by  these  surfaces  is  maintained.  While  this  of  necessity 
makes  a  much  larger  briquette,  it  would  seem  to  be  the  only  way  to  secure 
a  form  which  will  develop  the  real  strength  of  the  material,  y •  j 

321.  To  Find  the  Distribution  of  Stress  over  the  Minimum  Section  of  a 
Cement  Briquette. — The  following  is  a  development  of  the  theory  of  the 
distribution  of  stress  over  the  minimum  section  of  a  cement  briquette,  pub- 
lished by  M.  Durand-Claye  in  the  Annales  des  Fonts  et  Chaussees  in  June 
1895.*  Let  M  and  N,  Fig.  357,  be  the  points  of  application  of  the  external 


FIG.  357. 

forces  applied  to  the  briquette,  which  is  here  given  a  somewhat  conven- 
tional form.  As  a  result  of  the  application  of  the  vertical  forces  at  J/and 
JV  these  points  are  raised  to  Mf  and  N'  with  respect  to  the  fixed  axis  AB, 
through  the  distortion  of  the  specimen.  The  original  lines  NB,  NC,  and 

*  Prof.  Aug.  Foppl  (Bauschinger's  successor)  has  now  shown  that  a  greater  tensile 
stress  is  actually  developed  on  the  outer  fibres  of  stone  beams  than  can  be  obtained  on 
tension  specimens,  and  he  thinks  this  is  because  of  the  uneven  distribution  of  stress  over 
the  cross-section  of  the  tension-test  specimen.  (Communications  from  the  Munich 
Laboratory,  vol.  xxiv,  1896.) 


436  THE  MATERIALS  OF  CONSTRUCTION. 

NA  of  the  specimen  now  become  N'B,  N1  'C,  and  N'  A,  and  the  stresses  along 
these  lines  are  proportional  to  the  deformations  N'B  —  NB,  Nf  C  —  NO, 
and  N'A  —  NA,  respectively.  Similar  relations  exist  on  the  corresponding 
lines  drawn  from  J/.  The  total  stress  at  the  points  A,  C,  and  B,  therefore, 
will  be  equal  to  the  sum  of  the  vertical  components  of  the  stress  at  each 
point  arising  from  the  external  forces  at  the  two  points  of  application 
M  and  .V. 

Let  <x,  ft,  and  a'  represent  respectively  the  angles  which  the  three  lines 
from  N  to  B,  C,  and  A  form  with  the  vertical. 

Now  the  stretch  of  the  lines  ND,  NB,  NC,  and  NA  due  to  the  displace- 
ment NN'  is  as  1,  cos  at,  cos  ft,  and  cos  a',  respectively,  and  the  propor- 
tional stretch  of  a  line  is  the  total  stretch  divided  by  the  length  of  the  line; 
hence  the  proportional  stretch  of  these  lines  is  as  1,  cos2  a,  cos2  ft,  and  cos" 
a',  respectively. 

But  the  stress  is  as  the  proportional  stretch;  hence  the  stresses  along  the 
lines  NB9  NC,  and  NA  are  as  the  squares  of  the  cosines  of  their  respective 
angles  with  the  vertical.  Since  we  are  only  concerned  with  the  vertical 
components  of  these  stresses,  and  since  these  are  respectively  equal  to  the 
inclined  stress  into  the  cosine  of  the  same  angle,  the  vertical  stresses  at  B, 
C  and  A  due  to  the  external  force  at  JVare  to  each  other  as  cos3  a,  cos3  ft, 
and  cos*  a'. 

The  total  vertical  stress  at  each  of  these  points,  however,  is  the  sum  of 
the  two  stresses  arising  from  the  external  forces  at  both  M  and  N\  hence 
it  follows  that  if  we  represent  by  R  the  total  vertical  stress  at  A  and  B,  and 
by  r0  the  total  vertical  stress  at  C,  we  have 

R        cos8  at  +  cos3  at' 
r^~  2  cos3  ft 

By  trial  the  law  of  the  distribution  of  stress  over  the  section  A  B,  by 
equation  (1),  is  very  nearly  that  of  a  parabola.  Making  this  assumption, 
and  knowing  that  the  area  of  the  exterior  portion  of  the  rectangle  enclos- 
ing a  parabolic  segment  is  one  third  that  of  the  rectangle,  we  have,  for  the 
mean  stress  over  this  section, 


P  R 

r  =  ~=r,  +  ^(R-  r.)  =  —^-S.     ....     (2) 

where  P  =  total  breaking  strength  of  the  briquette  and  S  =  its  sectional 
area. 

For  the  three  forms  of  briquette  shown  in  Figs.  358,  359,  and  360  the 

values  of  —  ,  from  eq.  (1),  are  1.22,  2.04,  and  2.12,  and  the  values  of  the 

ro 

P 

average  stress  r  =  -     are,  from  eq.  (2),  1.14,  1.52,  and  1.54,  respectively. 


TESTING   OF  CEMENT. 


437 


\ff     0 

FIG.  358. — Showing  the  Distribution  of  Stress  in  the  Author's  Form. 


FIG.  359.— Showing  the  Distribution  of  Stress  in  the  German  Form. 


c       B  a 

FIG.  360.— Showing  the  Distribution  of  Stress  in  the  Standard  English  and  American 

Form. 


438  THE  MATERIALS  OF  CONSTRUCTION. 

The  last  of  these  forms  (Fig.  3GO)  is  the  standard  form  employed  in 
England  and  America,  and  is  that  recommended  by  the  Committee  of 
the  American  Society  of  Civil  Engineers.  The  second  (Fig.  359)  is  the 
standard  form  employed  on  the  continent  of  Europe,  and  is  commonly 
spoken  of  as  the  a  German  standard."  The  first  (Fig.  358)  is  a  form 
devised  by  the  author  to  give  a  more  even  distribution  of  stress  across  the 
minimum  section.  An  extended  series  of  tests  by  the  St.  Louis  Water 
Department  shows  results  on  neat  Portland  cement  over  25  per  cent  greater 
on  briquettes  of  the  form  shown  in  Fig.  358  than  was  obtained  on  exactly 
similar  briquettes  of  the  common  American  form  shown  in  Fig.  360.* 
These  higher  results  are  partly  due  to  the  improved  form  of  clips  shown 
in  Fig.  363. 

322.  The  Form  of  the  Moulds. — It  is  customary  to  use  single  moulds, 

though  multiple  or  gang  moulds  are  often 
used  where  great  numbers  of  briquettes  are 
to  be  made.  In  either  case  they  should 
be  made  in  two  parts,  as  shown  in  Fig.  361, 
so  as  to  be  easily  removed  after  the  samples 
have  set  without  danger  of  breaking  the 
FIG.  361.  test-specimens.  The  parts  may  be  held 

together  by  a  spring,  by  clamps,  or  by  a  latch.  They  should  always  be 
oiled  or  soaped  before  using,  to  prevent  the  cement  from  adhering  to 
them. 

Where  the  English  system  of  measures  is  used  it  is  now  common  to 
make  the  minimum  cross-section  of  the  briquette  1  inch  square.  It  has  been 
thought  that  the  strength  varied  with  the  size  of  the  section,  as  is  appar- 
ently proved  by  the  results  plotted  in  Fig.  362,  but  in  all  probability  this 
variation  can  now  be  explained  by  the  greater  inequality  in  the  distribution 
of  the  tensile  stress  over  the  larger  cross-sections.  At  least  it  seems  fair  to 
assume  this  to  be  the  case  until  it  has  been  disproved. 

323.  The  Clips — Their  Bearings  and  Mountings. — Next  in  importance 
to  the  form  of  the  briquette  is  the  character  of  the  clip  by  means  of  which 
the  briquette  is  broken.     The  essential  features  of  perfect  clips  are: 

1.  They  must  grasp  the  briquette  by  a  hard-cushion  bearing  on  four 
symmetrical  flat  surfaces. 

2.  They  must  be  freely  suspended  from  a  pivot  bearing,  so  as  to  turn 
without  friction  while  under  stress. 

3.  They  must  be  so  rigid  that  they  will  not  spread  appreciably  when 
subjected  to  their  maximum  load. 

The   first   requirement   is   necessary   in   order    to   avoid   crushing   the 

*  If  we  use  the  subscripts  a  and  b  to  distinguish  the  forms  in  Figs.  358  and  360 
respectively,  we  have,  since  Ra  =  Rb,  1.14r0  =  1.54r6>  or  ra  =  1.35r6.  That  is  to  say, 
the  form  shown  in  Fig.  358  should  be  35$  stronger  than  that  shown  in  Fig.  360. 


TESTING   OF  CEMENT. 


439 


briquette  by  the  concentration  of  the  load  on  a  line  or  on  a  few  points. 
Very  hard  rubber  pieces  should  be  dovetailed  into  the  metal  clips  at  the 
bearing-surfaces,  and  allowed  to  project  a  little  beyond  the  metal. 

When  the  second  requirement  is  satisfied  it  is  advisable  to  use  an  adjust- 
ing frame  for  placing  the  clips  symmetrically  on  the  briquette. 


FIG.  362.— Apparent  Varying  Tensile  Strength  of  Cement  for  Different  Areas  of  Cross- 
section  of  Briquette.     (Grant  and  Whittemore,  Engr.  News,  Dec.  14,  1893,  p.  468.) 

All  these  demands  are  well  satisfied  in  the  form  of  clip  and  adjusting- 
frame  shown  in  Fig.  363,  which  were  devised  by  the  author  to  be  used  with 
his  new  form  of  briquette  (Fig.  358).* 

These  clips  are  suspended  from  a  steel  point,  the  same  as  in  the 
German  (Michaelis)  machine.  The  hard-rubber  (gutta-percha)  pieces  R 
bear  directly  on  the  tangent  surfaces  of  the  briquette,  and  they  are  brought 
to  a  symmetrical  position  (after  the  briquette  is  placed)  by  means  of  the 
adjusting-frame,  which  is  set  over  the  screw-heads  at  top  and  over  the 
raised  guides  at  bottom  and  then  slipped  downwards  to  a  bearing.  The 
screw-clips  at  bottom  are  then  turned,  when  both  the  briquette-clips  are 
held  rigidly  against  the  adjusting-frame  and  in  their  true  position.  The 
movable  clip  is  then  screwed  down  to  a  hard  bearing  on  the  briquette,  and 
the  adjusting-frame  removed.  It  might,  however,  remain  on  throughout 
the  test  if  preferred,  and  in  fact  it  could  be  permanently  attached  to  the 
rear  sides  of  the  clips. 

*  Both  the  moulds  and  the  clips  with  their  adjusting-frame  are  made  by  Mahn  & 
Co..  instrument-makers,  St.  Louis,  Mo. 


440 


THE  MATERIALS  OF  CONSTRUCTION. 


These  clips,  used  on  briquettes  of  the  form  shown  in  Fig.  356,  greatly 
increase  the  breaking  strength  of  neat  Portland  cement. 


FIG.  363.— The  Author's  Form  of  Clip  and  Adjusting-frame.     Half-size, 
used  with  the  form  of  briquette  shown  in  Fig.  356 


To  be 


324.  The  Testing-machine. — On  the  Continent  Michaelis'  machine,  shown 
in  Fig.  3G4,  is  almost  universally  employed.  The  leverage  is  50  to  1,  and 
the  load  is  imposed  by  means  of  small  shot  which  escapes  from  a  reservoir 
into  the  weight-pan.  The  dropping  of  this  pan  when  the  specimen  breaks 
shuts  off  the  flow  of  shot.  The  pan  is  then  weighed,  and  its  weight,  multi- 
plied by  50,  (this  may  be  done  in  the  graduation  of  the  scales)  gives  the 
strength  of  the  briquette. 

A  very  neat  modification  of  this  machine  is  that  made  by  the  Fairbanks 
Scale  Co.  and  shown  in  Fig.  365.  It  is  entirely  self-contained  and  dis- 
penses with  both  the  auxiliary  reservoir  and  frame  and  the  weighing-scales. 
The  shot-pan  is  moved  from  the  end  of  the  weighing-lever  and  hung  from 


TESTING   OF  CEMENT. 


441 


the  hook  at  the  left,  and  a  weight-hook  hung  in  its  place  on  the  weighing- 
beam.  The  poise  is  then  moved  out  on  this  beam,  its  extreme  movement 
corresponding  to  a  load  of  200  pounds.  For  greater  loads  "  200-pound  " 
weights  are  placed  on  the  weight-hook  and  the  poise  moved  out  again  to 
balance.  In  both  the  machines  the  load  comes  on  gradually  and  without 


IBP 

FIG.  364.— Standard  Form  of  German  Cement-testing  Machine  for  Tension  Tests. 


FIG.  365. — The  Fairbanks  Cement- testing  Machine. 

shock  by  the  flow  of  the  shot,  which  is  automatically  shut  off  by  the  drop- 
ping of  the  beam,  and  the  rate  of  imposition  of  the  load  can  be  regulated 
by  varying  the  size  of  the  gate.  The  tightening-screw  P  is  first  turned  till 
the  weighing-beam  moves  to  its  highest  limit,  and  then  any  further  amount 
to  put  an  initial  stress  in  the  specimen  short  of  rupture,  after  which  the 


442 


THE  MATERIALS  OF  CONSTRUCTION. 


free  movement  of  the  weighing-beam  is  sufficient  to  break  the  specimen 
without  any  further  turning  of  the  tightening-screw.  The  clips  contain 
adjustable  bearings  intended  to  prevent  the  breaking  of  the  briquettes  in 
the  clips. 


77M 


lW 


20  40  #0  30          J00 

FIG.  366.— Effect  of  Varying  the  Rate  of  Loading  on  the  Tensile  Strength  of  Neat 
Portland-cement  Briquettes.     (Faija,  in  Trans.  Inst.  C.  E.,  vol.  75.) 


600 


£00         $00 

FIG.  367.— Effect  on  Tensile  Strength  of  Rate  of  Applying  Load.     (Wheeler,  Rep 
Chf.  Engrs.,  1895,  p.  2951.) 

The  machines  shown  in  Figs.  368  and  369  are  made  by  Messrs.  Riehle 
Bros,  and  by  Tinius  Olsen,  respectively,  both  of  Philadelphia.  They  both 
require  the  imposition  of  the  load  by  hand ;  but  as  this  is  through  a  screw- 
gear  and  is  very  slowly  applied,  there  would  seem  to  be  no  appreciable  un- 
steadiness in  it.  The  beam  is  kept  in  balance  at  the  same  time  by  the  same 
attendant,  by  moving  out  the  poise  till  rupture  occurs.  Evidently  the 
speed  here  is  entirely  under  the  control  of  the  operator,  and  both  these 
machin.es  give  entire  satisfaction. 


TESTING   OF  CEMENT. 


443 


In  all  these  testing-machines  the  grips  or  clips  are  swivelled  and 
mounted  in  such  a  way  as  to  allow  of  a  free  universal  movement,  or  adjust- 
ment of  these  to  the  specimen. 


FIG.  368  — Riehle  Cement-testing  Machine. 

Fig.  370  shows  the  construction  of  a  cement-testing  machine  designed 
and  used  by  Prof.  J.  M.  Porter.* 

"The  load  is  applied  hy  water  flowing  into  a  tank  suspended  from  the 
long  arm  of  a  very  sensitive  15-to-l  lever.  The  weight  of  the  lever  and 
tank  is  counterbalanced  by  an  adjustable  weight  shown  on  the  left.  Water 
is  admitted  to  the  tank  from  a  large  reservoir  on  the  roof  under  a  practi- 
cally constant  head  of  90ft.,  so  that  there  is  no  sensible  variation  of  pressure- 
in  the  stream  admitted  through  a  carefully  fitted  gate-valve  in  the  supply- 
pipe.  The  position  of  this  valve  at  "  on,"  "  off,"  and  all  intermediate  points 
is  shown  by  an  index  attached  to  the  stem  of  the  valve  and  registering  on  a 


*The  following  description  by  the  inventor  is  taken  from  the  Engineering  News  of 
March  5.  1896. 


444 


THE  MATERIALS  OF  CONSTRUCTION. 


dial  marked  off  with  the  number  of  pounds  per   minute   applied  to  the 
specimen  as  determined  and  verified  by  previous  experiment. 

"  When  the  briquettes  break,  the  lever  drops  a  few  inches,  then  the 
plunger  at  the  right  end  of  the  lever  enters  the  pneumatic  stop,  and  the 
lever  and  tank  are  gradually  brought  to  rest.  During  the  fall  of  the  tank, 
and  before  it  comes  to  rest,  a  chain  attached  to  the  end  of  the  valve- 
stem  in  the  tank  is  brought  into  tension  and  arrests  the  descent  of  the 


FIG.  369.— Olsen  Cement-testing  Machine. 

valve  before  its  seat  stops  descending.  The  opening  of  this  valve  allows 
the  contents  of  the  tank  to  be  quickly  discharged  into  a  hopper  placed 
upon  the  floor,  and  is  then  carried  off  through  a  waste-pipe  to  the  sewer. 
As  soon  as  the  tank  has  discharged  its  contents,  the  weight  ou  the  left  end 
of  the  lever  brings  the  lever  and  tank  into  the  position  shown  in  the  illus- 
tration, the  valve  taking  its  seat  during  this  movement,  and  the  machine  is 
ready  for  another  break.  The  actual  load  can  be  applied  at  from  0  to  80 
Ibs.  per  minute,  thus  giving  an  increase  of  stress  of  from  0  to  1200  Ibs. 


TESTING   OF  CEMENT 


445 


per  minute.  The  speed  generally  used  is  400  Ibs.  per  minute,  and  with 
the  valve  set  for  this  speed  the  needle-beam  will  float  every  time  within 
I  second  of  the  proper  time. 

"  The  stress  on  the  specimen  is  measured  by  a  poise  travelling  on  a  gradu- 
ated scale-beam,  which  can  be  read  by  means  of  a  vernier  to  1  Ib.  and  can 


be  moved  automatically  or  by  hand  at  the  wish  of  the  operator.     The  auto- 
matic movement  is  accomplished  by  the  following-described  device: 

"  The  horizontal  disk  and  its  engaged  friction-wheel  are  driven  continu- 
ously by  the  pulley  placed  at  the  lower  end  of  the  vertical  shaft  and  belted 
to  overhead  shafting.  This  friction-wheel  is  feathered  to  a  sleeve  that  runs 


446  THE  MATERIALS  OF  CONSTRUCTION. 

loose  on  its  shaft  and  carries  a  coned  clutch  that  is  nominally  disengaged 
from  its  cone,  which  is  also  feathered  to  the  shaft,  and  can  be  moved 
slightly  longitudinally  on  the  shaft  into  contact  with  the  clutch  by  the 
action  of  the  vertical  lever. 

"  When  the  needle-beam  rises,  it  makes  contact  through  a  vertical  pin  in 
the  top  of  the  frame,  which  completes  an  electric  circuit  and  sends  a  cur- 
rent through  the  electromagnet  and  causes  it  to  attract  its  armature  at  the 
lower  end  of  the  vertical  lever,  which  moving  to  the  right  engages  the  fric- 
tion-clutch and  causes  the  shaft  to  revolve.  This  shaft  operates  the 
sprocket-wheel  and  chain  which  draw  out  the  poise  on  the  scale-bearn  until 
the  needle-beam  drops,  breaking  the  electric  circuit.  Breaking  the  elec- 
tric circuit  releases  the  armature  and  allows  the  friction-clutch  to  disen- 
gage, and  the  poise  comes  to  rest.  The  friction-wheel  may  be  set  at  a 
greater  or  less  distance  from  the  centre  of  the  disk  by  turning  the  capstan- 
head  nut,  and  the  chain  is  overhauled  faster  or  slower,  causing  the  poise  to 
move  accordingly.  If  desired,  the  poise  may  be  operated  by  the  hand- 
wheel  without  interfering  with  the  automatic  device  other  than  cutting  out 
the  circuit.  The  chain  is  attached  to  the  poise  in  line  with  the  three 
knife-edges  of  the  scale-beam;  hence  the  tension  in  the  chain  has  no  ten- 
dency to  lift  up  or  pull  down  the  poise.  This  point  is  often  overlooked 
in  designing  this  detail,  not  only  in  cement  machines  but  in  testing-ma- 
chines in  general.  The  writer  [Prof  Porter]  has  a  cement  machine  in 
which  the  error  due  to  this  cause  is  over  15  Ibs. 

"  This  machine  as  described  has  been  in  almost  constant  use  for  eigh- 
teen months  and  has  given  entire  satisfaction.  The  operator  has  simply  to 
place  the  briquette  in  the  clips,  open  the  supply- valve,  wait  until  the  bri- 
quette breaks,  and  then  note  the  reading  on  the  scale-beam.  The  objection 
to  this  machine  is  the  space  it  occupies,  requiring  a  floor-area  of  7  X  2  ft., 
and  the  necessity  of  a  constant  head  of  water." 

325.  Importance  of  an  Exact  Central  Position  in  the  Clips. — It  was  shown 
in  Art.  26  that   if   h  —  width  of  specimen   and  a  —  eccentricity  of  load- 
ing, the  percentage  of  increase  in  the  stress  from  this  cause  is  given  by  the 

fraction  -^.     Thus  if  a  cement  briquette  1  inch  thick  be  placed  in  the  clips 

0.01  inch  out  of  centre,  its  strength  will  be  reduced  by  6  per  cent.  This 
assumes  perfect  freedom  of  motion  of  the  clips  at  the  surfaces  of  contact, 
which  they  do  not  have.  Experiments  made  at  the  Massachusetts  Institute  of 
Technology  *  have  shown  that  a  displacement  of  TV  inch  decreased  the  ten- 
sile strength  by  from  15  to  20  per  cent  (see  Fig.  371).  Vy 

326.  Compression  Tests  of  Cement  have  not  been  common  in  America, 
though  long  practised  in  Europe.     The  excellent  relation  indicated  in  Fig. 
337,  p.  419,  between  the  tensile  and  the  compressive  strength  of  Portland- 

*  Trans.  Am.  Soc.  Mech.  Engrs.,  vol.  ix.  p.  181. 


TESTING   OF  CEMENT. 


447 


cement  mortar  (1  C.  to  3  S.)  would  seem  to  show  that  both  tensile  and  com- 
pressive  tests  are  not  required,  and  American  engineers  have  always  acted 
on  this  assumption. 

The  French  Commission  recommend  compression  tests,  however,  in  addi- 
tion to  the  tension  tests,  but  they  do  not  advise  the  making  of  separate  test- 
specimens.  With  the  form  of  briquette  shown  in  Figs.  355  and  356  the  line 
of  rupture  is  definitely  fixed  (with  very  few  breaks  outside  the  grooved  sec- 
tion), and  hence  the  two  halves  of  the  broken  briquette  will  be  nearly  equal  to 
each  other  and  to  all  other  broken  parts.  These  ends  are  then  to  be  tested 


FIG.  371. — Showing  Effect  of  Eccentric  Position  of  Briquette  in  Clips.  (Assoc.  Eng.  Soc., 

vol.  vn.  p.  207). 

by  crushing,  the  force  to  be  applied  normally  to  its  bed,  and  the  sum  of  the  test 
loads  on  the  two  ends  of  one  briquette  to  be  the  crushing  strength  of  that 
specimen.  In  the  absence  of  such  broken  briquettes  to  serve  for  this  test, 
cylinders  of  the  same  area  and  height  are  to  be  made  up  anil  tested. 

Since  this  height  is  but  22  mm.,  while  the  diameter  of  the  equal  cylinder 
is  45  mm.  (Fig.  355),  the  specimen  has  a  height  of  but  one  half  its  lateral 
dimension,  and  hence  the  compressive  strength  of  such  a  form  of  specimen 
is  20  per  cent  greater  than  that  of  a  cubical  form  as  shown  in  Art.  22,  Fig.  17. 
The  broken  briquettes  are  chosen  to  avoid  making  up  additional  specimens, 
and  also  because  this  insures  identical  material  for  both  the  tension  and 
the  compression  tests.  For  instituting  a  comparison  with  the  compressive 
tests  on  otner  material,  where  the  cubical  form  has  been  almost  universally 
used,  the  correction  coefficient  of  0.83  can  be  employed,  as  stated  above, 
or  else  cubical  specimens  can  be  prepared  and  tested. 

It  ^s  of  course  necessary  to  prepare  all  compress!  ve-test  specimens  with 
care,  by  reducing  the  two  bearing-surfaces  to  true  planes.  It  would  also  be 
wise  to  provide  a  universal  joint  back  of  one  of  the  bearing-plates.* 

*  See  method  employed   at  the  Massachusetts  Institute  of  Technology,  Am.  Soc. 
Mech.  Engrs.,  vol.  ix.  p.  172. 


448 


THE  MATERIALS  OF  CONSTRUCTION. 


In  America  compression  tests  of  cement  are  made  on  the  universal  test- 
ing-machines so  common  in  this  country.  In  Europe  many  special  machines 
are  made  for  this  purpose,  one  of  the  most  recent  of  which  is  shown  in  Fig. 
372.  Here  the  load  is  indicated  by  the  position  of  the  radial  arm  moving 


FIG.  372.— Machine  for  Making  Tests  of  Cement  in  Compression.     (Manufactured  by 
Amsler-Laffon  &  Son,  Scbnffbausen,  Switzerland.) 

over  the  graduated  arc,  the  actual  movement  of  the  upper  head  being  thus 
multiplied  a  known  number  of  times.  As  this  movement  is  resisted  by  a 
powerful  helical  spring,  when  this  spring  has  been  standardized  its  compres- 
sion is  a  true  index  of  the  load. 

327.  Cross-bending  Tests  of  Cement  have  been  advocated  occasionally, 
but  they  have  not  come  into  genera]  nee  anywhere.   The  French  Commission 


TESTING  OF  CEMENT.  449 

have  also  undertaken  to  standardize  this  test.  They  recommend  a  specimen 
5  inches  (120  mm  )  long  and  0.8  inch  (20  mm.)  square  in  cross-section, 
and  they  show  how  this  specimen  may  be  broken  on  the  Michaelis  machine, 
Fig.  3G4,  by  attaching  the  centre-bearing,  upward-pulling  stirrup  to  the 
small  hook  at  the  left  end  of  the  lower  lever. 

M.  Du  rand -Clave  has  shown  by  very  extended  series  of  tests  in  tension 
and  in  cross-bending,  on  identical  samples  of  neat  Portland  cement,  that 
the  average  ratio  of  the  modulus  of  rupture  in  cross-bending  to  the  tensile 
strength,  as  determined  upon  standard  forms  of  briquettes,  is  1.92  at  7  days 
and  1.86  for  28  days,  or  an  average  of  1.89.*  This  relation  was  found  to 
subsist  between  averages  made  up  from  the  means  of  the  three  tests  in  each 
set  of  six,  in  both  tension  and  cross-bending.  The  mean  error  of  a  single 
test  at  28  days  was  found  to  be  2.10  per  cent  for  the  tension  tests  and  2.13 
per  cent  for  the  tests  in  cross-bending,  thus  showing  that  the  two  methods  of 
testing  were  equally  accordant. 

It  would  seem,  therefore,  that  tests  in  cross-bending  may  be  employed 
with  assurance  as  a  means  of  determining  both  relative  and  absolute  values 
of  cements  and  cement-mortars,  their  principal  disadvantage  lying  in  the  fact 
that  there  are  few  records  extant  with  which  tc  compare  the  results  of  such 
tests. 

The  principal  recommendation  for  the  use  of  transverse  tests  would  seem 
to  lie  in  the  economy  of  a  testing  outfit.  It  has  been  estimated  that  a 
suitable  machine  for  testing  cement  transversely  could  be  constructed  for 
about  $12,  while  a  set  of  moulds  for  sixteen  prisms  would  cost  not  to  exceed 
$3,  or  if  these  latter  be  made  of  cast  iron  the  cost  need  not  exceed  $5  per 
set  of  twelve  after  the  patterns  are  made.f 

It  is  further  claimed  that  since  all  transverse  breaks  are  fair,  while  with 
the  forms  of  briquettes  and  clips  hitherto  used  in  America  nearly  fifty  per 
cent  of  the  breaks  occur  outside  of  the  minimum  section,  the  results  of 
transverse  tests  must  be  more  reliable.  If,  however,  a  form  of  briquette 
and  clip  can  be  devised  which  will  always  give  fair  breaks,  this  claim  of 
advantage  will  no  longer  stand.  There  seems  to  be  now  in  this  country 
no  inclination  to  change  from  tension  to  transverse  tests  of  cement. 

328.  Standard  Tests  to  Determine  the  Adhesion  of  Cement-mortars  to 
Various  Substances. — While  the  tensile  strength  of  briquettes  shows  the 
cohesion  of  the  mortar,  it  has  been  found  by  experiment  that  its  adhesion 
either  to  other  mortars  or  to  the  same  mixture  which  has  already  hardened, 
or  to  brick  or  stone  or  metal,  is  very  much  less  than  its  cohesion.  It  is 
important,  therefore,  to  have  a  standard  test  of  adhesion,  as  well  as  of 

*  Messrs.  Abbott  and  Morrison,  in  their  thesis  published  in  Engineering  News,  Dec. 
14,  1893,  show  that  for  neat  cement  this  ratio  was  1.8  on  prisms  one  inch  square  and 
broken  on  a  span  of  four  inches. 

f  See  Engineering  News,  vol.  xxx.  p.  469,  where  complete  detail  drawings  are 
given  of  both  the  machine  and  of  the  moulds. 


450 


THE  MATERIALS  OF  CONSTRUCTION. 


strength.  Because  tests  of  this  kind  are  comparatively  new,  no  general 
custom  has  been  established  in  America  on  the  subject;  but  the  following 
recommendations  have  been  made  by  the  French  Commission: 

(1)  For  tests  of  adhesion  of  cements  and  cement-mortars  use  will  be 
made  of  a  special  form  of  briquette,  moulded  in  two  parts,  these  two  parts 

consisting  of  the  two  materials  whose  adhe- 
sion is  to  be  tested,  provided  both  cai\  be 
moulded,  or  containing  between  them  a 
prism  of  the  solid  body  to  which  the  adhe- 
sion of  the  mortar  is  to  be  determined  The 
form  of  this  briquette,  as  modified  for  Eng- 
lish units,  with  one  square  inch  of  area  on 
the  surface  of  adhesion,  is  shown  in  Fig. 
373.  This  mould  is  formed  in  two  parts, 
and  is  used  to  form  in  succession  the  two 
halves  of  the  complete  briquette. 

(2)  To  compare  the  force  of  adhesion  of 
different  cements  to  a  given  material,  nor- 
mal adhesion-Nocks  will  be  prepared  as  fol- 
lows: Use  for  these  always  one  kind  *of 
standard  Portland  cement  which  has  passed 
a  sieve  of  eighty  meshes  to  the  linear  inch, 

mixed  with  the  standard  sand  No.  3  (see 
FIG.  373.— Form  of  Briquette  for    .    ,    oim  .     ,,  ,.          ,,  ,, 

A  ,,  m    ,  Art.  317)  m  the  proportion  01  one  01  cement 

Adhesion    Test    of    Cement    as 


-  ,1 
\ 

C" 

-/"  -^ 

/        ^ 

adopted  by  the  French  Commis- 


to    two    of    sand-     These    normal  adhesion- 

sion    and    adapted    to   English  blocks  will  be  moulded  in  the  form  of  one 
Units.  half  of  the  briquette  shown  in  Fig.  373.* 

It  will  be  gauged  with  9$  of  water  and  rammed  into  the  mould.  At  the 
end  of  2-i  hours  in  air  it  will  be  placed  in  fresh  water  for  a  period  of  at 
least  twenty-eight  days.  When  it  is  to  be  used,  it  will  first  be  dried  and  its 
adhesion-surface  polished  with  emery-paper. 

(3)  The  cement  to  be  tested  for  adhesion  with  these  standard  blocks 
prepared  as  above  will  be  mixed  as  a  normal  plastic  mortar,  one  of  cement 
to  three  of  sand  (see  Art.  316),  which  will  be  introduced  into  the  mould 
with  a  trowel,  this  mould  now  being  placed  with  a  normal  adhesion-block  at 
the  bottom  in  place  of  the  movable  metallic  disk.  The  mould  will  remain 
upon  this  completed  block  until  it  is  ready  for  testing,  and  the  block  will 
be  allowed  to  harden  either  in  air  or  water,  and  for  such  period  as  the  test 
requires.  It  is  recommended  that  the  number  of  tests,  the  periods  of  time, 
the  methods  of  hardening,  and  the  recording  of  the  results  should  comply 
with  the  conditions  given  for  tension  tests  in  Art.  319. 


*  The  detail  drawings  of  these  moulds  are  given  in  the  Fr.  Com.  Rep.,  vol.  iv.  p.  284. 


TESTING   OF  CEMENT.  451 

(4)  To  compare  the  force  of  adhesion  of  a  given  cement  to  different  mate- 
rials. For  this  purpose  the  test-specimens  will  be  prepared  as  described 
above,  except  that  in  place  of  the  normal  adhesion-blocks  similar  blocks  of 
the  various  materials  to  be  tested  will  be  prepared  and  allowed  to  harden, 
provided  these  are  such  as  can  be  moulded  in  this  manner.  If  such  mate- 
rials are  solid,  small  disks,  about  three-eighths  of  an  inch  thick,  will  be  pre- 
pared, and  these  will  be  used  in  the  bottom  of  the  mould  in  place  of  the 
metallic  disk,  the  adhesion-block  to  be  completed  by  using  neat  Portland- 
cement  mortar.  After  this  has  hardened  the  briquette  will  be  completed 
by  making  the  other  half  of  a  standard  plastic  mortar,  one  cement  to  three 
of  sand,  using  the  particular  kind  of  cement  whose  adhesion  to  these 
various  substances  is  to  be  tested. 

If  the  normal  plastic  mortar  is  not  used  in  adhesion  tests,  a  full  descrip- 
tion of  its  composition  should  be  indicated  on  the  records. 

These  adhesion-briquettes  to  be  broken  on  a  standard  tension-testing 
machine,  using  the  regular  tension-clips. 

329.  Normal  Variations  in  Volume  of  Cement-mortars  in  Air  and  in 
Water. — From  elaborate  tests  on  the  swelling  and  shrinking  of  cement-mor- 
tars hardening  in  air  and  under  water  made  at  the  Massachusetts  Institute 
of  Technology,  Boston,  and  by  Professor  Bauschinger  at  Munich,  it  may  be 
stated : 

1.  Cement-mortar  hardening  in  air  shrinks  almost  uniformly  for  a  period 
of  more  than  three  months,  the  linear  shrinkage  in  that  time  being,  for  neat 
cement,  from  0.12  to  0.3-1  of  one  per  cent,  and  for  cement-mortar,  one  of 
cement  to  one  of  sand,  from  0.08  to  0.17  of  one  per  cent.     The  change  in 
volume  is  of  course  three  times  the  above  percentages. 

2.  Cement-mortars   hardening   under  water  increase   in    linear  dimen- 
sions from  0.04  to  0.25  of  one  per  cent  in  three  months  for  neat  cement,  and 
from  0.00  to  0.08  of  one  per  cent  for  a  mortar  composed  of  one  part  cement 
to   one    of   sand;    the    volumetric    expansion    being    three    times    these 
amounts. 

Professor  Bauschinger  found  for  nine  German  Portland  cements,  neat, 
an  expansion,  when  hardened  under  water,  of  0.05  of  one  per  cent  in  sixteen 
weeks;  Mr.  Grant  found  for  English  Portland  cement  an  expansion  of  0.08 
of  one  per  cent  in  three  months,  this  latter  figure  agreeing  with  the  average 
results  of  the  tests  made  on  eight  kinds  of  Portland  cement  at  the  Massa- 
chusetts Institute.* 

For  mortars  composed  of  one  part  of  cement  to  three  of  sand  the  varia- 
tions in  volume  are  very  much  less  than  those  given  for  mortars  of  equal 
parts  of  sand  and  cement. 

*  See  progress  reports  of  committee  of  the  Am.  Soc.  C.  E.  on  the  compressive  strength 
of  cements,  vol.  xvn.  p.  215,  and  vol.  xvni.  p.  264. 


452  THE  MATERIALS  OF  CONSTRUCTION. 

330.  Recommendations  of  the  French  Commission  for  Testing  Perma- 
nency of  Volume. — Tests  of  permanency  of  volume  may  be  of  two  general  classes — 
cold  and  hot. 

Cold  Tests  will  be  made  upon  thin  cakes  of  neat-cement  paste  made  up  on  glass, 
about  six  inches  in  diameter  and  f  inch  thick  at  the  centre,  with  thin  edges,  and 
placed  immediately  in  water  or  in  air,  along  with  the  briquettes  which  are  hardening 
in  these  two  media.  These  cakes  to  be  examined  at  periods  of  7  days,  28  days,  3 
months,  6  months,  1  year,  2  years,  etc.,  corresponding  to  the  like  periods  for  the  tests 
of  strength. 

To  measure  the  amount  of  the  linear  change  of  volume  of  neat  cement  immersed 
in  cold  water,  a  small  cement  form,  32  inches  long  and  ^  inch  square  in  section,  may 
be  moulded  and  placed  vertically  in  a  glass  tube  1  inch  in  diameter  filled  with  water. 
The  expansion  would  be  indicated  by  the  movement  of  the  long  arm  of  a  lever  over 
a  graduated  scale,  which  is  actuated  by  a  pin  embedded  in  the  upper  end  of  the 
specimen  when  made.* 

Evidently  it  may  require  years  to  assure  one  of  the  permanency  of  volume,  or 
soundness,  of  a  cement  by  the  use  of  the  cold-water  and  air  test. 

Hot  Tests  to  be  made  on  cylinders  of  neat  cement  1J  inches  (30  mm.)  high  and 
1 J  inches  in  diameter,  made  up  and  left  in  metal  moulds  composed  of  sheet  metal  0.02 
inch  (0.5  mm.)  thick  (No.  25  gauge).  This  mould  to  be  entirely  severed  on  one 


>| 

FIG.  374. — Apparatus  for  Testing  Permanency  of  Volume  of  Cement.     (Recommended 

by  the  French  Commission.) 

element,  and  to  have  soldered  to  it  on  the  opposite  side  two  arms,  six  inches  long, 
forming  an  angle  with  each  other  as  shown  in  Fig.  374.  The  decreasing  distance  be- 
tween the  extremities  of  these  arms  to  be  a  measure  of  the  swelling  of  the  cement. 

These  moulds  to  be  immersed  in  cold  water  as  soon  as  filled,  and  allowed  to  set 
for  24  hours,  or  for  a  shorter  period  if  it  is  a  quick-setting  cement.  The  mould  will 
then  be  placed  on  a  grating  in  a  vessel  of  water  and  its  temperature  raised  to  the 
boiling-point  in  from  15  to  30  minutes.  This  temperature  is  to  be  maintained  for 
six  hours,  when  the  water  will  be  allowed  to  cool  down  before  removing  the  speci- 
men for  remeasuring  the  distance  between  the  six-inch  arms. 

This  hot  test  not  to  be  applied  to  natural  cements,  or  to  any  cement  which  sets 
very  rapidly. 

The  consistency  of  the  cement  used  in  both  the  hot  and  the  cold  tests  to  be  of  the 
normal  consistency  described  in  Art.  316. 

331.  The  Permeability  of  Cement-mortar  is  often  a  very  important  mat- 
ter, as  in  the  case  of  reservoir  wells  and  linings,  and  often  in  foundation- 
walls  placed  below  the  level  of  the  ground-water.  Neat  cement-mortar 
is  absolutely  impervious  when  it  has  hardened  and  has  not  cracked, 
and  so  also  is  a  mixture  of  one  to  one,  or  even  of  two  of  sand  to  one  of 
*  See  Fig.  25,  p.  302,  vol.  i,  Report  of  the  French  Commission,  1895. 


TESTING   OF  CEMENT. 


453 


cement,  by  weight,  if  well  mixed.     The  normal  mixture  of  three  of  sand 

to  one  of  cement   may  also  be  made  practically  impervious  with  the  most 

thorough    mixing   of    the   dry  ingredients 

and   a  compacting   of  the  mortar  by  hard 

ramming. 

Professor  Tetmajer  has  used  the  appara- 

tus shown  in  Fig.  375  to  obtain  a  modulus  of 

permeability.    Here  a  cylinder  of  the  mortar 

is  made  and  allowed  to  harden  under  water 

for  a  specified  time.     It  is   then   mounted 

in  the  apparatus  by  means  of  annular  rubber- 

cushion  or  packing  disks,  and  the  water  let 

on  below    under  a  known    pressure.      The 

permeability  of  the  mortar  is  indicated    by 

the  rate  at  which  the  water  passes  the  disk 

and  rises  in   the   glass  tube  above,   which 

is   graduated    to    cubic   centimeters.      The 

author   has   also   used    this  apparatus  with 

satisfactory  results,   a   convenient   pressure 

to  use  being  that  of  the  city  water-mains. 

The  French  Commission 
recommend  a  standard  per- 
meability test  as  follows: 

(I)  The  permeability  of 
cement-mortars  will  be  indi- 

cated by  the  number  of  liters  of  water  passing  per  hour 
through  a  cubical  block  of  7  cm.  (say  2|  inches)  on  a  side, 
under  the  following  conditions. 

The  water  will  be  brought  to  the  top  face  of  the  specimen, 
laid  edgewise  (what  was  the  horizontal  plane  in  the  forma- 
tion of  the  cube  now  becoming  a  vertical  plane),  through  a 
glass  tube,  35  mm.  internal  diameter  and  about  4  or  5  inches 
high,  which  is  sealed  to  the  top  face  of  the  cube  by  neat 
cement-mortar  as  shown  in  Fig.  376.  A  rubber  tube  con- 
the  upper  end  of  the  glass  tube  with  the  reservoir 


FIG.  375. — Tetmajer's  Apparatus 
for  Testing  the  Permeability  of 
Cement  -  mortar.  (Communica- 
tions, vol.  vi.  1 


Fm.     376. 
lestmg       the 


placed  at  a  height  (from  the  surface  of  the  water  of  immer- 
Permeability  s*on  ^°  ^ie  surface  °^  the  water  in  the  reservoir)  of  4  inches, 
of  Cement-mor-  40  inches,  or  400  inches  (0.1  m.,  1.0  m.,  or  10.0  m.). 
tar.       (Recom-        Before  beginning  the  experiment  the  cube  of  mortar  to 
mended  by  the  be  immersed  in  water  for  48  hours,  and  during  the  test  the 

nch     ^om-  block  is  to  remain  immersed  to  prevent   the  formation  of  an 
mission.)  .  .  ,.  , ,  ,   .  ,     » 

impervious  coating  on  the  outside  irom  the  evaporation  of 

the  exuding  water. 

The  volume  of  water  passing  will  be  given  for  the  standard  periods  of 


454  THE  MATERIALS  OF  CONSTRUCTION.  ' 

24  hours,  7  days,  28  days,  and  3  months.  For  very  porous  mortar  a 
shorter  period  than  24  hours  may  be  employed,  and  at  the  same  time  the 
head  of  water  used  must  be  stated. 

Tests  will  be  made  on  three  similar  specimens,  the  mean  of  the  two  most 
accordant  results  to  be  used. 

(2)  The  normal  test  of  permeability  will  be  made  on  cubes  made  up  of 
normal  plastic  mortar  (3  sand  to  1  cement,  by  weight)  as  described  in  Art. 
319,  and  the  specimen  cubes  must  harden  in  water  under  the  normal  con- 
ditions for  28  days  before  testing. 

For  tests  on  other  mixtures,  and  for  other  periods  of  hardening,  they 
recommend  that  mixtures  of  2  sand  to  1  cement,  and  5  sand  to  1  cement,  by 
weight,  and  hardening  periods  of  7  days,  28  days,  and  3  months  be  chosen. 

In  all  cases  the  composition,  age,  and  conditions  of  hardening  must  be 
stated,  as  well  as  the  amount  of  water  passed  and  the  pressure-head  used. 

332.  Tests  for  the  Decomposing  Action  of  Sea-water. — As  a  result  of  the 
porosity  of  cement-mortars  and  concretes  and  of  the  resulting  action  of  sea- 
water  on  the  interior  of  the  mass,  producing  therein  certain  changes  partly 
by  solution  and  partly  by  the  formation  of  new  chemical  compounds,  cement- 
mortars  and  concretes  are  often  disintegrated  when  subjected  to  the  action  of 
sea-water.  The  French  Commission  have  carefully  studied  this  question, 
and  have  recommended  the  following  test,  which  they  regard  as  of  value  in 
determining  the  comparative  resistance  of  cement  to  this  action: 

(1)  Standard  tension  briquettes  of  normal  plastic  mortar  (one  cement  to  three  of 
sand)  will  be  made,  and  after  24  hours  in  air  will  be  placed  in  sea-water  which  is  to 
be  renewed  every  two  days  during  the  first  week',  and  every  week  thereafter.    During 
the  first  week  the  volume  of  this  sea-water  to  be  at  least  four  times  that  of  the  bri- 
quettes immersed  in  it. 

An  equal  number  of  duplicate  briquettes  to  be  exposed  in  a  similar  manner  to  the 
action  of  fresh  water.  Tension  tests  on  these  duplicate  briquettes  to  be  made  at  the 
standard  periods  of  28  days,  3  months,  6  months,  1  year,  etc.,  and  the  effect  of  the 
sea-water  to  be  shown  by  a  comparison  of  the  results. 

(2)  Filtration  tests  will  be  made  on  specimens  having  a  cubical  form,  as  described 
in  Art.  331,  and  to  be  exposed  to  the  action  of  sea-water  both  in  the  bath  and  in  the 
filtration  reservoir  there  described.     The  head  will  be  4  inches,  40  inches,  or  400 
inches,  according  to  the  permeability  of  the  specimen.     Two  sets  of  duplicate  test- 
specimens  will  be  subjected  to  this  test,  one  having  hardened  in  sea-water  and  the 
other  having  hardened  in  air  for  the  several  standard  periods  chosen. 

A  third  duplicate  set  of  exactly  similar  cubical  blocks  to  be  preserved  and  hard- 
ened in  fresh  water  for  the  same  periods  of  time. 

In  the  absence  of  actual  sea- water,  artificial  sea- water  will  be  prepared  with  the 
following  formula: 

Chloride  of  sodium  (NaCl) 30  g. 

Sulphate  of  magnesia,  crystallized  (MgOSO3,7H2O) 5 

Chloride  of  magnesium,  crystallized  (MgCl,6H2O) 6 

Sulphate  of  lime,  hydrated  (CaOSO3,2H2O) 1.5 

Bicarbonate  of  potassium  (KOH2O,2CO3) 0.2 

Distilled  water 1000 

All  the  above  cubes  to  be  superficially  examined  and  tested  in  compression  at  the 
standard  periods  chosen. 

The  following  observations  will  be  taken: 


TESTING   OF  CEMENT.  455 

(a)  The  comparative  appearance  of  the  specimen  subjected  to  the  several  kinds 
of  treatment. 

(6)  The  tensile  strength  of  the  two  sets  of  briquettes  which  had  hardened  in 
salt  and  in  fresh  water. 

(c)  The  compressive  strength  of  the  three  sets  of  cubical  blocks  which  had  hard- 
ened in  salt  water  and  in  air,  and  which  had  been  subjected  to  the  filtration  tests, 
and  the  blocks  which  had  hardened  in  fresh  water. 

(d)  Chemical  composition  of  the  cubical  blocks  subjected  to  the  several  kinds  of 
treatment. 

For  other  compositions,  mortars  composed  of  one  cement  to  two  of  sand,  and  one 
cement  to  five  of  sand,  to  be  chosen  and  tested  at  the  standard  periods  of  7  days,  28 
days,  3  months,  etc. 


CHAPTER  XXII. 

TESTS  OF  THE    STRENGTH   OF    STONE   AND   BRICK. 
TESTS  OF  STONE. 

333.  Tests  of  the  Strength  of  Stone  Limited  to  the  Crushing  Test. — 

Since  stone  can  readily  be  prepared  for  crushing  tests,  these  have  been 
almost  exclusively  employed  in  determining  its  strength.  In  view  of  the  data 
obtained  from  comparative  tests  of  cement  in  tension  and  compression  shown 
in  Fig.  337,  p.  419,  it  might  be  inferred  that  the  crushing  test  would  show 
also  the  relative  strength  in  tension.  Since  failure  in  crushing  is  a  failure 
by  shearing,  it  might  be  supposed  that  the  true  relative  shearing  strength 
would  also  be  shown  by  the  compression  test.  When  stone  fails  in  cross- 
bending  it  breaks  first  on  the  tension  side  of  the  beam,  and  hence  this  is  a 
failure  in  tension,  and  therefore  the  crushing  test  has  been  thought  to  give 
correct  relative  values  of  cross-breaking  strength. 

These  assumptions  prove  not  to  be  correct,  however,  as  has  been  very 
conclusively  shown  by  Bauschinger  in  volumes  x,  xvn,  and  xix  of  his 
Communications,  where  the  results  of  tests  on  more  than  a  thousand  speci- 
mens of  building-stones  of  the  various  kinds  found  in  Bavaria  are  given. 
These  tests  were  made  in  compression,  in  tension,  in  cross-bending,  and  in 
shearing,  and  no  fixed  relation  can  be  given  to  these  several  kinds  of 
strength.  Probably  this  is  largely  due  to  the  fact  that  stones  are  not  amor- 
phous bodies,  but  are  usually  either  sedimentary  or  crystalline  or  both,  with 
definite  planes  of  cleavage  and  of  weakness.  Since  stone  is  used,  however, 
almost  exclusively  in  compression,  it  is  usually  considered  sufficient  to  test 
its  strength  in  compression  only. 

The  conditions  to  be  fulfilled  in  the  crushing  test  of  stone  are  sufficiently 
elucidated  in  Chapters  III  and  XVI.  While  the  test-specimens  should  have 
heights  greater  than  their  least  lateral  dimensions,  yet  in  order  to  make  the 
results  comparable  with  those  hitherto  obtained  and  recorded  it  is  necessary 
to  continue  to  make  these  tests  on  cubical  forms. 

TESTS    OF   PAVING-BBICK. 

334.  Kinds  of  Tests  Required. — The  use  of  brick  for  the  wearing  sur- 
face of  street -pavements  is  now  so  universal  that  this  new  product,  "  vitri- 

456 


TESTS  OF  THE  STRENGTH  OF  STONE  AND  BRICK.  457 

fied  paving-brick,"  has  become  one  of  the  most  important  of  the  materials 
employed  by  the  civil  engineer.  Since  appearances  in  this  material  are 
entirely  untrustworthy,  and  since  these  products  vary  greatly  not  only  as 
between  the  output  of  different  manufacturers,  but  also  as  between  different 
kilns  of  the  same  factory  or  even  in  different  parts  of  the  same  kiln,  a 
thorough  system  of  mechanical  tests  to  determine  the  probable  wearing 
qualities  is  absolutely  essential.  To  develop  these  qualities  four  tests  are 
now  commonly  accepted  as  essential,  namely  *  : 

1.  Cross-breaking. 

2.  Crushing. 

3.  Impact  (the  rattler  test). 

4.  Absorption. 

335.  The  Cross-breaking  Test.  —  This  is  made  on  single  whole  bricks  by 
setting  them  edgewise  on  two  rounded  knife-edge  bearings  about  7  inches 
apart  and  loading  them  at  the  centre.  In  order  to  insure  a  true  bearing  of 
the  knife-edges  the  brick  should  be  ground  to  true  parallel  surfaces,  or  else 
the  lower  bearings  should  be  rounded  longitudinally  sufficiently  to  prevent 
a  twisting  or  torsional  action.  The  cross-breaking  modulus  of  rupture  is 
found  by  applying  the  formula 

3TP7 


336.  The  Crushing  Test  is  usually  made  on  a  half  -brick,  set  edgewise, 
and  one  or  both  of  the  ends  of  the  brick  previously  used  in  the  cross-break- 
ing test  may  be  used.     As  these  faces  are  very  rough  in  paving-brick  (from 
their  having  been  reduced  to  a  semi-plastic  condition  in  the  kilns,  these 
being  the  bearing-surfaces),  it  is  impossible  to  make  fair  crushing  tests  on 
these  forms  without  grinding  them  to  true  parallel  planes.     This  can  readily 
be  done  on  a  regular  stone-  or  marble-grinding  table  operated  by  steam- 
power,  such  being  available  in  all  large  cities.     When  this  is  done  they  may 
be  bedded  on  single  thicknesses  of  tar-board,  or  placed  directly  between 
steel  plates  in  the  testing-machine.     Great  care  must  be  exercised  to  place 
the  specimen  centrally  in  the  machine,  and  to  see  that  the  bearing-plates 
fit  evenly  upon  the  specimen.     One  of  these  plates  should  have  a  spherical 
base  to  make  it  adjustable  and  so  insure  an  even  and  true  bearing  on  the 
test-specimen.     The  specimen  should  fail  all  at  once,  with  a  loud  report, 
with  little  or  no  previous  spalling.     The  load  must  be  increased  very  slowly 
and  uniformly,  and  the  weighing-beam  automatically  balanced  if  practicable. 

337.  The  Rattler  Test.  —  Formerly  this  test  was  made   as  an  abrasion 
test  by  using  a  great  quantity  of  small  castings.     The  author  has  long  in- 
sisted that  this  test  should  partake  of  the  character  of  an  impact  test,  and 
this  view  now  generally  prevails.     Paving-brick   are  broken  to  pieces   in 
service  rather  than  worn  or  ground  down,  and  the  property  of  resilience 
is  the  one  sought  rather  than  hardness.     The  standardizing  of  this  test 

*  See  Recommendations  of  a  Committee  of  the  National  Association  of  Brick  Maun- 
facturers,  in  Art.  338. 


458 


THE  MATERIALS  OF  CONSTRUCTION. 


has  proved  a  difficult  task,  but  it  has  been  fairly  accomplished  by  Mr. 
F.  F.  Harrington,  a  former  student  of  the  author's,  now  in  charge  of  the 
Testing  Laboratory  of  the  Board  of  Public  Improvements  of  the  City  of 
St.  Louis.  Mr.  Harrington's  rattler  is  a  cast-iron  barrel,  polygonal  in  form 
and  having  fifteen  staves,  similar  to  that  shown  in  Fig.  377.  Its  length 
is  42  inches  and  its  diameter  is  24  inches,  and  it  revolves  on  trunnions  at 


FIG.  377. — Rattler  for  Testing  Paving-brick. 


'flftfl 


S%          /<?  /J  #?          23% 

FIG.    378. — Rattler  Test  of  Brick  showing  Maximum  Impact-effect  when  the  barrel 
has  15$  of  its  volume  filled  with  brick.     (Harrington.) 

the  ends.     A  movable  cast-iron  partition  can  be  inserted  on  the  inside  so  as 
to  shorten  the  length  of  the  part  used  to  any  amount  less  than  42  inches. 


TESTS  OF  THE  STRENGTH  OF  STONE  AND  BRICK. 


459 


It  is  operated  by  an  electric  motor  which  is  also  used  for  other  purposes 
in  the  laboratory. 

Fig.  378  shows  the  results  of  placing  different  amounts  of  brick  in  the 
barrel.  Evidently  there  would  be  a  particular  amount  (percentage  of 
volume)  whichwould  give  a  maximum  impact-effect.  This  proves  to  be 
15$.  That  is  to  say,  when  15$  of  the  volume  of  the  interior  of  the  barrel 
is  filled  with  brick,  solid  measure,*  the  impact-effect  was  a  maximum,  the 
barrel  making  30  revolutions  per  minute.  This  quantity  was  then  adopted 
as  the  quantity  of  material  always  to  use. 


FIG.  379.— Showing  the  Effects  of  Time  in  the  Rattler  Test  of  Paving-brick 

(Harrington.) 

In  Figs.  379  and  380  the  effects  of  time  and  speed  are  shown  when  the 
standard  quantity  of  brick  (15$)  was  in  the  barrel.  Since  the  60-minute 
curve  gave  an  even  20$  less  at  30  revolutions  per  minute,  this  being 
regarded  as  about  the  proper  amount,  this  product,  of  1800  revolutions,  was 
chosen. 

The  effect  of  the  length  of  the  barrel  is  shown  in  Fig.  381,  all  being 
filled  to  15$  of  the  total  volume.  It  will  be  seen  that  the  length  of  the 

*This  means  that  the  total  solid  contents  of  the  brick  equals  15*  of  the  volume 
of  the  barrel. 


460 


THE  MATERIALS  OF  CONSTRUCTION. 


barrel  has  no  sensible  influence  on  the  tests,  provided  it  is  always  filled  to 

!:he  same  percentage  of  its  volume. 

338.  Standard  Tests  of  Paving-brick. — As  a  result  of  these  experimental 

tests,  and  of  similar  ones  carried  out  by  Prof.  Edward  Orton,  Jr.,  of  the  Ohio 

State   University,  chairman,  a  committee  of  the  National  Association  of 

Brick  Manufacturers  of  America,  appointed  in  Feb.  1896   reported  in  Feb. 

1897,  recommending  the  following  tests  as  standard:* 

1.  A  rattler  test,  made  in  a  cast-iron  rattler  28  inches  in  diameter  and 

20  inches  long,  having  fourteen  flat  sides  with  one-fourth-inch  spaces  inter- 
vening. The  rattler  to  be  filled  with 
a  number  of  any  given  kind  of  brick 
equalling  in  total  volume  15$  of  the 
volume  of  the  rattler  (requiring  1800 
cu.  in.  of  brick  volume,  or  from  20 
to  24  brick  for  this  standard  size). 
The  rattler  to  be  run  1800  revolu- 
tions at  the  rate  of  30  revolutions 
per  minute.  In  no  case  must  a  dif- 
ierent  kind  of  brick  or  other  material 
be  used  to  make  up  the  charge. 
Other  sizes  of  rattler,  from  26  inches 
to  30  inches  diameter  and  other 
lengths,  could  be  allowed,  and  the 
speed  might  vary  between  24  and 
36  revolutions  per  minute. 

Two  such  tests  on  any  given 
species  of  brick  to  constitute  a 
standard  rattler  test,  and  the  aver- 
age result  to  constitute  the  record. 
This  result  to  be  a  given  percentage 
of  loss  of  weight  in  terms  of  the  orig- 
inal weight.  The  individual  bricks 
20  40  £0  <30  do  not  need  to  be  identified  in  the 

FIG.  380. — Showing  the  Effects  of  Various  two  weighings  in  this  test. 

Speeds  in  the  Rattler  Test  of  Paving-          3    A  cross-breaking  test  (number 
brick.     (Harrington.)  of   ^  not  gtated)    tQ    be  made  ^ 

described  in  Art.  335,  the  lower  knife-edges  to  be  rounded  to  radii  of  15 
inches  longitudinally  and  -J  inch  transversely.  The  span  to  be  6  inches. 

3.  A  crushing  test  as  described  in  Art.  336,  or  with  the  undressed  bear- 
ing surfaces  embedded  in  plaster  of  paris. 

Tests  2  and  3,  for  strength,  were  not  regarded  by  the  committee  as 
essential,  but  were  made  optional 


*  The  author,  on  invitation,  participated  in  the  proceedings  of  this  committee. 


TESTS  OF  THE  STRENGTH  OF  STONE  AND  BRICK. 


461 


The  absorption-test  was  condemned  as  misleading,  inasmuch  as  no  brick 
which  could  endure  the  proposed  rattler  test  would  ever  absorb  enough 
water  to  injure  it;  while  if  the  test  be  used,  a  thoroughly  vitrified  (glassy) 
brick  might  be  preferred  to  a  semi-vitrified  one  because  of  its  smaller 
absorption. 

It  will  thus  be  observed  that  the  committee  regarded  the  rattler  test,  as 
here  proposed,  as  quite  sufficient  to  determine  the  wearing  and  weathering 
qualities  of  paving-bricks.  This  test  alone  requires  from'40  to  50  brick  to 
be  furnished,  since  it  is  to  be  made  in  duplicate.  As  a  matter  of  conven- 


#• 


l> 

^  i  £  A/  G  T  tf 


jffffli 


K  wre/#Tj0f  #f  m  f/M£0f£Mft£i  wwt 


of 


7T//t//V/T£/?/M=/S% 
4   /?    ft    £    Z 


/2  ?/  30  33 

FIG.  381. — Showing  Effect  of  Length  of  Ban-el  in  the  Rattler  Test  of  Paving-brick. 

(Harrington.) 

ience,  therefore,  the  rattler  should  be  made  double,  or  so  as  to  contain  two 
apartments  having  the  dimensions  described  above.* 

The  first  effect  observed  in  the  rattler  test  is  one  of  chipping  on  all 
edges.  After  these  have  rounded  off  somewhat  the  effect  is  more  evenly 
distributed  over  the  outer  surface,  but  it  still  remains  principally  an  impact 
action.  The  dust  and  small  pieces  fall  through  the  spaces  left  between 
staves  for  this  purpose,  so  that  the  rattler  remains  comparatively  clear  of 
debris.  If  absorption-tests  are  made,  they  should  be  made  on  bricks  which 
have  passed  the  rattler  test,  because  their  glazed  surfaces  are  then  broken, 
if  not  largely  removed. 

Accordant  results  could  not  be  obtained  when  different  kinds  of  brick 
were  put  in  the  rattler  at  one  time  or  when  other  materials,  such  as  stone, 
granite,  or  cast-iron  blocks,  were  employed;  hence  the  requirement  that 
the  full  complement  of  material  in  the  rattler  should  consist  of  the  brick 
tested. 

No  specified  requirements  were  named  by  the  committee,  as  sufficient 
data  had  not  yet  been  obtained. 


*  Standard  drawings  and  patterns  for  such  a  rattler  have  been  prepared  by  Mr.  M. 
L.  Hoi  man,  Water  Commissioner  of  St.  Louis,  from  which  the  author  has  had  a 
machine  constructed. 


CHAPTER  XXIIL 
TESTS  OF  THE  STRENGTH  OF  TIMBER. 

339.  The  Variable  Strength  of  Timber.—  As  shown  in  Chapter    XIII, 
sound  timber  of  a  given  species   varies  in   its  strength  from  two  general 
causes,  its  structure  and  its  moisture  condition.     Neither  of  these  sources 
of  strength  (or  weakness)  has  hitherto  received  proper  study  and  analysis, 
and  hence  the  known  variations  in  the  strength  of  timber  has  been  attrib- 
uted either  to  its  inherent  and  undiscoverable  variations,  or  to  variations 
iii  the  size  of  the  sticks  tested.     Some  of  the  most  important  conclusions 
to  be  drawn  from  the  U.  S.  Timber  Tests  are: 

1.  The  strength  of  timber  is  about  twice  as  great  ivhen  it  is  dry  as  when 
it  is  green  or  wet.* 

2.  The  strength  of  a  given  species  of  timber  at  a  given  percentage  of 
moisture  is  governed  by  the  ratio  of  the  summer  (solid)  to  the  spring  (open) 
wood,  or  in  other  words  by  its  specific  gravity  or  solidity. 

3.  The  strength  per  square  inch  of  a  large  stick  in  every  kind  of  test  is 
fully  equal  to  that  of  a  smaller  stick  cut  from  it  ivhen  both  are  similarly 
proportioned  and  similarly  free  from  faults. 

4.  It  is  very  highly  probable  that  the  strength  of  all  kinds  of  wood-fibre 
of  like  structural  arrangement  (thus  putting  the  oaks  into  a  separate  class) 
increases  directly  with  the  specific  gravity  (or  weight  per  cubic  foot)  of  the 
dry  wood.     (See  a  discussion  of  this  subject  in  Chapter  XXXII.) 

The  moisture  state  is  the  great  and  governing  cause  of  variation  in 
strength.  When  reduced  to  the  same  moisture  condition  it  may  be  said,  as 
a  result  of  about  40,000  tests  of  timber  made  by  the  author,  that  in  crushing 
endwise  90  per  cent  of  all  tests  fall  within  25  per  cent  of  the  mean,  and 
55  per  cent  of  all  tests  fall  within  10  per  cent  of  the  mean-value  for  that 
species,  and  this  is  about  as  much  as  can  be  said  for  other  kinds  of  building 
materials  when  all  have  been  subjected  to  a  reasonable  inspection. 

340.  "  The  United  States  Timber  Tests,"  f  so  called,  were  inaugurated  in 
1891  by  Dr.  B.  E.  Fernow,  Chief  of  the  Forestry  Division  of  the  U.  S. 
Agricultural  Department,  and  have  been  carried  on  with  frequent  inter- 
ruptions  ever  since.     They  consist  of  a  very  complete  series  of  investiga- 

*  Sec  the  curve  showing  variation  of  strength  with  moisture  in  Chapter  XXXII. 

f  See  Bulletins  6,  8,  10,  13,  and  others  to  be  issued  from  time  to  time  by  the  U.  S. 
Agricultural  Department,  Forestry  Division,  and  to  be  had  on  application  to  the  chief  of 
that  division. 

462 


TESTS  OF  THE  STRENGTH  OF  TIMBER.  463 

tions  into  the  habitat,  conditions,  and  laws  of  growth,  structure,  strength, 
and  other  properties,  seasoning,  preservation,  and  decay,  and  finally  the  arti- 
ficial cultivation  of  the  useful  timbers  of  the  United  States.  The  great  im- 
portance of  the  timber  industry  (being  second  only  to  that  of  agriculture  in 
this  country),  and  the  universal  absence  of  accurate  (scientific)  knowledge 
on  these  subjects,  have  seemed  to  warrant  the  undertaking  and  prosecution 
of  this  the  greatest  series  of  physical  investigations  ever  carried  out.  The 
field-studies  and  the  collection  of  the  material  have  been  done  by  Dr. 
Charles  Mohr;  the  structural  investigations  have  been  made  by  Mr.  Filibert 
Eoth  in  Washington;  and  the  mechanical  tests  have  been  made  under  the 
direction  of  the  author  in  his  testing  laboratory  at  Washington  University, 
St.  Louis,  Mo.  The  species  examined  and  tested  to  date  (December,  1896) 
are  given  in  tabular  form  in  Chapter  XXXII.  It  there  appears  that  there 
have  been  selected  for  these  tests — 

1.  Sixty-eight  trees  of  Long-leaf  Pine  *  from  South  Carolina,  Alabama, 
Mississippi,  Louisiana,  and  Texas. 

2.  Twelve  trees  of  Cuban  Pine  from  South  Carolina,  Georgia,  and  Ala- 
bama. 

3.  Twenty-two  trees  of  Short-leaf  Pine  from  Alabama,  Missouri,  Arkan- 
sas, and  Texas. 

4.  Thirty-two  trees  of  Loblolly  Pine  from  South  Carolina,  Georgia,  Ala- 
bama, and  Arkansas. 

5.  Seventeen  trees  of  White  Pine  from  Michigan  and  Wisconsin. 

6.  Eight  trees  of  Red  (Norway)  Pine  from  Michigan  and  Wisconsin. 

7.  Four  trees  of  Spruce  Pine  from  Alabama. 

8.  Twenty  trees  of  Bald  Cypress  from  South  Carolina,  Mississippi,  and 
Louisiana. 

9.  Four  trees  of  White  Cedar  from  Mississippi. 

10.  The  test  specimens  of  Douglas  Spruce  were  not  taken  from  selected 
trees,  but  were  obtained  from  lumber  shipments  to  the  St.  Louis  markets. 

11-20.  Eighty-three  trees  of  ten  species  of  Oak  from  Alabama,  Missis- 
sippi, and  Arkansas. 

21-27.  Twenty-four  trees  of  seven  species  of  Hickory  from  Mississippi. 

28-29    Five  trees  of  two  species  of.  Elm  from  Mississippi  and  Arkansas. 

30-31.  Four  trees  of  two  species  of  Ash  from  Mississippi. 

32.  Seven  trees  of  Sweet  Gum  from  Mississippi  and  Arkansas. 

Besides  these  a  great  many  small  trees  were  taken,  from  which  disks  were 
cut  at  frequent  intervals,  from  butt  to  top,  and  sent  to  Washington  for  the 
physical  and  structural  studies  Complete  field  notes  were  taken,  also,  of 
the  geographical  position,  the  immediate  surroundings  as  to  forest  growth, 
character  of  soil,  moisture  conditions,  etc.  The  diameter  of  the  stump,  the 
age  of  the  tree,  and  the  distance  to  the  first  limb  were  also  noted. 

*  Sixteen  of  these  were  "  bled  "  trees  to  determine  the  effects  of  "  boxing." 


464 


THE  MATERIALS  OF  CONSTRUCTION. 


All  this  material  has  come  from  the  Southern  States  except  the  white  and 
Norway  pines.  The  trees  have  been  selected  and  cut  by  Dr.  Mohr;  the  logs 
cut  from  them  were  shipped  to  the  author  at  St.  Louis  in  car-load  lots. 
Disks  8  inches  long  have  been  taken  from  all  these  trees,  at  a  number  of 
heights,  and  also  from  many  trees  of  the  same  species  too  small  for  timber- 
test  specimens,  and  sent  to  Mr.  Roth  at  Washington.  The  logs  have 
been  cut  into  test-timbers  in  various  ways  as  shown  in  Fig.  352.  The 
largest  forms  are  full-sized  beams  (from  the  18-foot  logs)  and  columns  (from 
the  12-foot  logs),  the  size  depending  on  the  size  of  the  log.  The  intermedi- 
ate forms  are  4  inches  square,  the  standard  size  of  the  "  small  "  sticks.  The 


No.  1. 


No.  2. 


No.  3. 


No.  4.  No.  5.  No.  6. 

FIG.  382.— Showing  Methods  of  Sawing  U.  S.  Timber  Test  Logs. 

smallest  size  is  2  inches  square,  which  has  been  employed  only  in  "special 
investigations."  The  form  in  No.  6  indicates  that  two  or  three  large 
sticks  are  to  be  cut  and  tested  to  failure,  from  the  uninjured  portions  of 
which  are  afterwards  cut  smaller  sticks  which  are  also  tested  for  the  pur- 
pose of  comparing  the  strength  of  large  and  small  sizes.  Form  No.  5  has 
been  adopted  as  the  standard  method  of  cutting  when  only  4-inch 
sticks  are  taken.  Only  logs  over  24  inches  in  diameter  at  the  small  end. 
could  furnish  this  entire  system  of  sticks,  smaller  logs  giving  the  five  interior 
ones  only.  The  logs  are  always  laid  out  on  their  upper  ends,  taking  the 
pith  as  the  centre  of  the  diagram  regardless  of  how  unsymmetrical  this  may 


TESTS  OF  THE  STRENGTH  OF  TIMBER.  465 

lie  in  the  cross-section  of  the  log.  The  logs  are  always  12  or  18  feet  in 
length,  and  the  4-inch  test-sticks  are  cut  to  6-foot  lengths,  thus  getting 
two  or  three  such  lengths  from  each  4-inch  stick  shown  in  the  log  diagram. 

341.  The  Mechanical  Tests. — As  a  rule  the  following  tests  have  been 
applied  to  every  4-inch  stick: 

1.  Cross-bending. 

2.  Crushing  endwise  of  the  grain. 

3.  Crushing  across  the  grain. 

4.  Shearing  along  the  grain. 

5.  Tension. 

Since  June  1895  no  tests  have  been  made  in  tension,  as  it  was  thought 
this  kind  of  strength  was  so  great  as  to  remove  it  from  the  category  of  pos- 
sible methods  of  failure.  It  was  thought  timber  would  never  fail  in  pure 
tension  in  practice. 

For  each  and  every  test  a  section  of  the  stick  about  T3F  inch  thick  is  cut 
from  near  the  point  of  failure,  and  used  for  determining  the  percentage  of 
moisture  as  described  in  Art.  343. 

The  test-sticks  were  subject  to  a  system  of  inspection  and  rejection 
which  it  was  thought  would  correspond  to  such  a  system  in  actual  practice 
where  the  timber  was  to  be  used  in  structures  where  the  parts  are  propor- 
tioned to  their  loads,  and  hence  it  is  thought  the  average  of  all  the  results 
fairly  corresponds  to  such  an  average  strength  in  practice  at  similar  stages 
of  dry  ness. 

In  order  to  make  the  results  comparable  it  was  of  course  necessary  to 
reduce  them  all  to  equivalent  values  at  a  standard  percentage  of  moisture. 
For  all  reductions  made  previous  to  May  1896  this  standard  had  been  15  per 
cent  moisture,  computed  on  the  dry  weight.  After  that  date  12  percent  was 
chosen  as  better  representing  the  condition  of  the  roughly  seasoned  timber, 
whether  in  or  out  of  doors.  In  a  dry,  heated  building  the  moisture  falls  as 
low  as  8  or  10  per  cent. 

342.  The  Cross-bending  Test  on  the  4-inch  sticks  is  made  on  a  small 
8000-lb.  testing-machine  designed  by  the  author,  shown  in  Fig.  301,  page 
370,  while  the  large  beams  are  tested  on  the  100,000-lb.  machine  shown  in 
Fig.  302,  page  371.     In  both  cases  the  loads  are  applied  so  as  to  produce  a 
uniform  rate  of  deflection  (with  the  4-inch  sticks  it  is  always  at  the  rate  of 

1  inch  per  minute,  while  with  the  larger  sticks  it  is  |  inch  per  minute)  in 
order  to  eliminate  the  time-effect,  which  is  very  large  with  timber  especially 
under  the  higher  loads. 

With  the  small  sticks  two  central  bearing-points  are  used,  12  inches 
apart,  thus  putting  that  length  of  stick  under  the  maximum  bending-stress, 
and  so  really  testing  12  inches  in  length  of  the  stick  instead  of  about  1  or 

2  inches  with  a  single  bearing.*     Of  course  in  all  cases  the  bearings  are 

*  This  was  done  as  the  effect  of  a  paper  by  Prof.  J.  Burkett  Webb  before  the  Am. 
Assoc.  Adv.  Science,  Section  D,  at  Rochester,  N.  Y.,  1892. 


466  THE  MATERIALS  OF  CONSTRUCTION. 

spread  over  a  considerable  area  by  means  of  steel  plates  to  prevent  the  de- 
struction of  the  fibres  by  crushing  across  the  grain.  With  the  large  beams, 
an  oak  saddle  some  30  inches  long,  of  the  full  width  of  the  beam,  and 
rounded  slightly  on  the  bottom  in  a  longitudinal  direction,  is  used  for  the 
centre  bearing  under  the  knife-edge  of  the  machine. 

The  deflections  of  the  small  beams  are  measured  by  means  of  a  microm- 
eter-screw bearing  on  the  head  of  the  power-screw,  as  shown  in  Fig.  301, 
while  in  the  case  of  the  large  beams  a  thread  was  stretched  (by  a  rubber  band) 
along  one  or  both  sides  from  nails  in  the  neutral  plane  above  the  end  bear- 
ings, and  readings  taken  on  a  scale  tacked  to  the  t}eam  at  the  centre.  The 
scale  was  nickel-plated  and  kept  polished  to  act  as  a  mirror,  and  the  par- 
allax of  the  thread  on  the  scale  was  obviated  by  Bringing  the  thread  and  its 
image  into  coincidence  when  the  readings  were  taken.  The  readings  were 
made  to  0.001  inch  with  the  small  beams  and  'to  0.01  inch  with  the  large 
beams. 

The  formulas  of  reduction  for  strength,  modulus  of  elasticity,  and  resil- 
ience were  adapted  to  the  particular  method  of  test  employed;  but  since  the 
resilience  in  inch-pounds  per  cubic  inch  is  different  for  the  two  cases  (single 
and  double  bearings  at  centre),  the  larger  results*  obtained  with  a  double 
bearing  have  been  reduced  to  their  equivalent  for  a*  single  bearing  to  make 
them  all  comparable  with  each  other  and  with  the  results  usually  obtained, 
which  would  be  with  a  single  bearing.  The  resilience  of  a  beam  loaded  at 
the  centre,  in  inch-pounds  per  cubic  inch,  is  from  eq.  6,  p.  84. 

_L  /! 

"  18    E 

This  is  also  the  measure  of  the  resilience  of  the  outer  ends  of  the  beams 
tested  with  double  bearings  at  the  centre,  while  for  the  part  between  the  two 
centre  bearings,  where  the  bending  moment  is  uniform,  it  is,  from  eq.  10, 
p.  85. 

!_/! 
"  12    E' 

The  /  being  the  same  in  the  two  cases,  namely,  the  "  apparent  elastic 
limit"  of  the  material,  found  by  fixing  a  point  of  the  bending-stress  diagram 
where  the  rate  of  deformation  is  50^  greater  than  at  the  origin,  as  explained 
in  Art.  13,  p.  18. 

The  results  obtained  from  each  cross-bending  test  of  timber,  therefore, 
are: 

1.  Modulus  of  strength  at  the  "apparent  elastic  limit." 

2.  Modulus  of  strength  at  rupture. 

3.  Modulus  of  elasticity. 

4.  Modulus  of  resilience,  or  springiness. 

When  large  beam  shave  been  tested  to  failure,  two  smaller  (4-inch)  beams 
6  feet  long  have  been  cut  from  the  upper  side  of  the  larger  beam  at  one  end, 


TESTS   OF  THE  STRENGTH  OF  TIMBER. 


467 


and  two  from  the  lower  side  at  the  other  end,  and  these  four  small  beams 
have  been  subjected  to  the  same  test  to  discover  whether  or  not  the  ordinary 
formulae  are  correct,  or,  what  is  the  same  thing,  to  discover  whether  the  same 
values  of  the  moduli  named  above  would  be  obtained  from  both  sizes.  All 
the  tests  which  have  been  made  of  this  kind  go  to  show  that  when  both  sizes 
are  equally  free  from  faults  this  is  true.  This  proves  that  the  strength  of 
large  sizes  may  safely  be  computed  from  tests  on  smaller  sizes,  other  things 
being  equal. 

343.  The  Crushing-endwise  Test. — For  this  test  a  section  about  8  inches 
long  of  the  uninjured  portion  of  a  4-inch  beam  which  had  been  tested  in 
cross-bending,  is  taken  by  means  of  a  circular  cutting-off  saw,  and  tested  to- 
failure  in  compression  endwise.  The  stress-diagrams  in  this  test  are  fairly 
indicated  in  Fig.  383.  Failure  occurs  by  a  buckling  down  of  the  fibres  as 
shown  at  B,  Fig.  113,  page  241.  After  this  buckling  action  of  the  fibres 
across  the  entire  section  has  occurred  the  strength  of  the  specimen  is  only 
about  0.8  what  it  had  been  originally,  as  is  shown  in  Figs.  29  and  383, 


o   a/0  0.20  a<3#  &f0  aw       0.70 

FIG.  383. — Typical  Stress-diagrams  of  Timber  when  subjected  to  Compression  Endwise. 

this  residual  strength    remaining   about  constant    for  largely   increasing 
deformations. 

This  is  the  most  valuable  and  characteristic  single  test  to  which  timber 
can  be  subjected.  It  is  the  only  one  in  which  a  relatively  large  stick  can  be 
evenly  and  simultaneously  tested  to  failure  throughout  its  entire  cross- 
section.  It  should  be  expected,  therefore,  to  give  more  uniform  results  than 


468  THE  MATERIALS  OF  CONSTRUCTION. 

any  other,  and  such  proves  to  be  the  case.  It  is  also  the  simplest  and  easiest 
to  make.  For  commercial  purposes,  therefore,  this  test  alone  would  serve 
nearly  every  purpose,  all  the  other  various  kinds  of  strength  and  stiffness 
being  inferred  from  this  one  test. 

344.  Crushing  Across  the  Grain. — Since  timber  is  very  weak  in  crush- 
ing across  the  grain,  as  compared  to  crushing  endwise,  this  is  found  to  be 
one  of  the  most  common  methods  of  failure  in  practice.     It  is  common  to 
rest  a  timber  column  on  a  sill  of  the  same  wood,  and  to  design  the  column 
for  its  maximum  working  load,  paying  no  attention  to  the  utter  inability  of 
the   sill  to  carry  this  load   without  crushing.       Many  failures   of   timber 
structures  are  due  to  this  cause  alone. 

As  there  is  no  definite  point  of  failure  in  crushing  across  the  grain,  two 
limits  of  deformation  have  been  arbitrarily  chosen  at  which  the  load  has 
been  recorded,  namely,  at  three  per  cent  compression,  as  a  working  limit 
allowable,  and  at  fifteen  per  cent  compression,  as  an  extreme  limit,  or  as 
failure.  The  apparatus  used  to  indicate  these  two  limits,  for  heights  (thick- 
nesses) of  specimen  from  2  inches  to  4  inches,  is  shown  in  Fig.  292  and  ex- 
plained in  the  text  of  Art.  282,  p.  357.  With  such  timber  as  oak,  which 
has  large  medullary  or  pith  rays,  the  crushing  strength  in  a  radial  direction 
is  greater  than  in  a  tangential  direction. 

345.  The  Shearing  Test. — This  is  intended  to  develop  the  strength  of 
timber  to  resist  shearing  along  the  grain.     This  strength  is  very  small  in 
nearly  all  kinds  of  wood,  and  may  be  reduced  almost  to  zero  by  seasoning 
checks.     It  is  a  very  common  method  of  failure  in  timber  framework,  and 
hence  it  is  important  to  test  for  it.     The  apparatus  used  is  illustrated  and 
described  in  Art.  300,  p.  386. 

346.  The  Tension  Test. — The  tensile  strength  of  timber  is  so  great  (often 
over  30,000  Ibs.   per  square  inch)  that  it  is  difficult  to  make  a  fair  test  of 
timber  in  this  way.     Simple  shouldering  is  out  of  the  question,  since  the 
specimen  shears  out  or  the  shoulders  crush  down.     The  author,  after  trying 
various  methods,  adopted  the  simple  forms   of   specimens  shown  in  Fig. 
113,  p.  241.     This  figure  does  not  show  the  reduction  of  the  cross-section 
at  the  centre,  which  was  done  by  cutting  out  two  segments  of  circles  on  the 
two  sides  by  a  band-saw,  these  segments  having  about  an  18-inch  radius. 
The  reduced  section  left  at  the  centre  of  the  specimen  was  about  3  inches 
by  f  inch,  making  something  over  a  square  inch  of  net  section.     These 
specimens  were  then   gripped  by  flat,  grooved,  cast-iron   wedges,  in  the 
100,000-lb.  universal  testing-machine,   and  pulled  to  failure.     Of  course 
nearly  straight-grained  timber  must  be  used  or  the  failure  is  partly  or 
wholly  one  of  shearing.     This  test  was  finally  abandoned  altogether,  as  it 
was  assumed  that  timber  would  never  fail  in  practice  in  this  way. 


PART   IV. 

THE  MECHANICAL  PROPERTIES   OF  THE  MATERIALS   OF 
CONSTRUCTION  AS  REVEALED  BY  ACTUAL  TESTS. 


CHAPTER   XXIV. 

THE  STRENGTH   OF   CAST   IRON. 

347.  The  Tensile  Strength  of  Cast  Iron  varies  from  15,000  to  35,000  Ibs. 
per  square  inch,  while  ordinary  foundry  irons  run  from  18,000  to  22,000' 
Ibs.*  This  strength  depends  greatly  on  the  size  of  the  specimen  as  well  as 
on  the  composition,  and  on  its  freedom  from  internal  stress  from  a  too 
rapid  cooling. 

The  general  characteristics  of  cast  iron  when  tested  in  tension  are 
shown  in  Figs.  384  and  385.  It  will  be  seen  that  there  is  here  no  well- 


FIG.  384.— Two  Stress-diagrams  of  Cast  Iron  in  Tension,  each  the  average  of  eleven  tests. 
Average  tensile  strength  =  33,500  Ibs.  per  square  inch.     (Wat.  Ars.  Rep.  1894.) 

defined  "  elastic  limit,"  and  if  there  be  such  a  point  it  is  very  low  in  com- 
parison with  the  ultimate  strength  of  the  iron.  The  "apparent  elastic 
limit "  falls  at  about  15,000  Ibs.  per  square  inch  (Fig.  385),  or  at  about 


*  When  annealed  in  the  malleable  process  its  strength  is  raised  to  from  30,000  to 
50,000  Ibs.  per  square  inch,  as  shown  in  Chapter  VII,  p.  115. 

469 


470 


THE  MATERIALS  OF  CONSTRUCTION. 


of  the  ultimate  strength,  as  is  found  to  be  the  case  with  wrought  iron  and 
rolled  steel.     The  permanent  set  at  this  point,  while  it  looks  large  in  Fig. 


Or 


CQ 


PWP0A 


///7Z 


o 

FIG.  385. — Typical  Stress-diagram  of  Cast  Iron  in  Tension,  with  Location  of  the  "Ap- 
parent Elastic  Limit,"  corresponding  to  a  permanent  set  of  0.0001  of  the  length. 
(Wat.  Ars.  Tests,  1892.) 

385,  is  in  reality  only  about  T^  of  one  per  cent,  or  entirely  inappreciable. 
It  is  safe  to  specify  25,000.  Ibs.  tensile 
strength,  if  great  strength  is  required. 
Mr.  AY.  J.  Keep  has  shown  (Fig.  57,  p.  96) 
that  the  cross -breaking  strength  is  very 
largely  a  function  of  the  size  of  the  test- 
specimen.  As  tension-test  specimens  are 
usually  cast  about  1  in.  to  1^  in.  in  diameter, 
this  variation  with  size  is  not  so  important 
for  tension-test  purposes  as  it  might  appear 
from  this  diagram.  The  test-specimens  are 
usually  turned  down,  both  at  the  gripped 
ends  and  on  the  reduced  portion.  Fig.  386 
shows  a  form  of  cast-iron  test -specimen 
which  is  intended  to  dispense  with  turning 
altogether;  but  even  here  it  would  be  better 
to  turn  the  gripped  ends,  to  avoid  all  bend- 
ing stresses  in  the  grips. 


FIG.  386.  —  Form  of  Cast-iron 
Specimen  \vhich  does  not  re- 
quire turning  down. 


THE  STRENGTH  OF    CAS?  IRON. 


471 


TABLE  XXIII. — COMPOSITION  AND  STRENGTH  OF  HIGH-GRADE  CAST  IRONS 
MADE  AT  THE  FOUNDRY  AT  THE  U.  S.  ARSENAL  AT  WATERTOWN,  MASS. 
TEST-SPECIMENS  GROOVED.  (Rep.  1894,  p.  247.) 


Composition  of  Charge. 

Kind  of  Furnace. 

Carbon. 

Manganese. 

Silicon. 

Sulphur. 

Phosphorus. 

!i 

go 

•a 

d 
'& 

A 
03 

O 

Combined. 

Tensile  Stre 
per  square 

Muirkirk  pig                35.  3  "1 

cupola 
do 

do 

do 
do 

air-furnace 
cupola 

do 

air-furnace 
cuoola 

2.440 
2.391 

2.487 

3.558 
2.279 

2.492 
2.393 

2.727 

2.058 
2.255 

0.900 
0.960 

0.744 

0.608 
0.366 

0.739 
0.432 

0.299 

0.778 
0.731 

0.335 
0.342 

0.461 

0.451 
0.353 

0.448 
0.450 

0.462 

0.464 
0.458 

1.137 
1.081 

1.511 

1.212 
1.024 

1.231 
1.090 

1.363 

1.560 
1.297 

0.113 
0.134 

0.118 

0.125 
0.118 

0.125 
0.140 

0.125 

0.115 
0.114 

0.572 
0.505 

0.521 

0.655 
0.496 

0.816 
0.497 

0.477 

0.619 
0.491 

27,700 
27,990 

31,980 

32,400 
34,453 

32,980 
31,110 

31,810 

29,100 
30,750 

16.07 
15.20 

17.35 

15.83 

20.47 
18.09 

Old  8-inch  shell  29.4  | 
Heads            29.4  ! 

Scrap                             .           5  9  | 

100     J 
Muirkirk  pig                          35  31 

Shell                        29  4 

Heads                                      29.4  ! 

Scrap  5.  9  f 

100"  j 

Richmond  pig  No.  1  10     1 
Richmond  pig  No.  2  10 

Salisbury  pig  No.  4,  high     15     V 
Scrap               50 

100     J 

Salisbury  pig  No.  4  27.51 
Salisbury  pig  No.  4,  high     275 
Scrap                                       45.0  > 

100     j 

Salisbury  pig  No.  4,  high     50     "| 
Salisbury  pig  No  4      .        50      ! 

100     j 

Salisbury  pig  No.  4  33.31 
Salisbury  pig  No.  4,  high    11  .  1  | 
Soft  pig  22.21 
Remelted  pig      33.3  f 

100     J 

Salisbury  pig  No.  4  25     1 
Salisbury  pig  No.  4,  high     25 
Scrap          .               .  .          50     >• 

100     J 

Richmond  pig  No.  1  11.1") 
Richmond  pig  No.  2  11.1 
Salisbury  pig  No.  4  16.7 

Salisbury  pig  No.  4,  high     16.7 
Scrap                             .          44  4 

100     J 

Salisbury  pig  No.  4.  33.3") 
Salisbury  pig  No.  4,  high     11.1 
Soft  pig                                   22  2  ! 

Remelted  pig  33.3  [ 

}00     J 

Salisbury  pig  No.  4  20     | 
Salisbury  pig  No.  4,  high     20 
Soft  pig  20 

Scrap               .                        40 

100     , 

472  THE  MATERIALS  OF  CONSTRUCTION. 

COMPOSITION   AND    STRENGTH   OF   HIGH-GRADE   CAST   IRONS — continued. 


g 

Carbon  . 

-•§ 

c  .5 

Composition  of  Charge. 

& 

3 

1 

% 

o> 

o 

^ 

«3 

3 

CO  cS 

I 

o 

Ic 

IS 

& 

c 

^ 

p« 

-—  CT* 

a 

•O 

p. 

E 

s 

§ 

B1 

I 

'Z  f-1 

"g 

a 

o 

6 

cS 

55 

's 
to 

oi  53 
£-1  P< 

aj 

K 

Richmond  pig  No.  1  9.41 

Richmond  pig  No.  2  9.41 

Salisbury  pig  No.  4  9.4  I 
Salisbury  pig  No.  4,  high      9.4  }• 
Scrap  62.5  1 

cupola 

2.890 

0.458 

0.388 

1.645 

0.105 

0.487 

27,320 

100     j 

Muirkirk  pig             ...       .38.51 

Soft  pig         23.0  | 

air-furnace 

2,538 

0,979 

0.348 

1.316 

0.130 

0.642 

26,480 

15.  6T 

Remelted  pig  38.51- 

100     J 

Salisbury  pig  No.  4  9.61 

Salisbury  pig  No.  4,  high      9.6 

Richmond  pig  No   1               96 

Richmond  pig  No.  2  9.61 
Soft  pig  23.1  f 

do 

2,770 

0,256 

0.470 

2.444 

0,110 

0,587 

28,010 

Remelted  pig.                       38  5 

100     J 

Salisbury  pig  No  4        .        8.31 

Salisbury  pig  No.  4,  high      8.3 
Richmond  pig  No.  1  8.3 

Richmond  pig  No.  2  ....     8.3  ! 
Soft  pig  20.  0| 

do 

2.751 

0.357 

0.435 

1.908 

0.095 

0.420 

29,120 

11.08 

Remelted  pig  46.7 

100     J 

Salisbury  pig  No.  4...          33.31 

Salisbury  pig  No.  4,  high    11.1 

Soft  pig  22.2 
Remelted  pig  33  3  f 

do 

2.538 

0.634 

0.355 

1.222 

0.090 

0.766 

28,520 

21.04 

100     J 

Salisbury  pig  No.  4  33.31 
Salisbury  pig  No.  4,  high     11.1 

Soft  pig  22.2, 
Remelted  pig  33.3  f 

do 

2.577 

0.185 

0.361 

1.146 

0.115 

0.762 

31,020 

100~j 

Salisbury  pig  No.  4  33  .  3  1 

Salisbury  pig  No.  4,  high     11.1 
Soft  pig  22.2  , 
Remelted  pig  33.3  f 

do 

2.116 

0.640 

0.450 

1.419 

0.125 

0.678 

31,140 

17.44 

100     J 

Salisbury  pig  No.  4  22.5  ] 
Salisbury  pig  No.  4,  high    22.5  | 

Scrap                                       55  0  }• 

fMTnnln 

2  825 

047Q 

0.361 

1.062 

0.076 

0.238 

32,010 

16.82 

100~J 

*  ^<  y 

Salisbury  pig  No.  4  8.31 
Salisbury  pig  No.  4,  high      8.3 
Richmond  pig  No.  1  8.3 

Richmond  pig  No.  2  8.3  ' 
Soft  pig  20  0  r 

air-furnace 

2.481 

0.687 

0.454 

1.175 

0.120 

0.673 

31,990 

Remelted  pig  46.7 

100     J 

THE  STRENGTH  OF  CAST  IRON. 


473 


The  tensile  strength  and  the  relative  hardness  of  various  high-grade 
compositions  are  given  in  Table  XXIII. 

348.  The  Compressive  Strength  of  Cast  Iron  varies  from  60,000  to  200,000 
pounds  per  square  inch  as  shown  in  Fig.  55,  p.  94.  In  Fig.  387  is  shown  a 


3M00 


OPC, 


flT/L 


MAT\£ 


$S/tf/ 


o         -402        m        006         m        M 

FIG.  387.— Average  Results  of  Twenty-two  Tests  of  Cast  Iron  in  Compression,  from 
B.  L.  12-iu.  Rifle-mortars.     (Wat.  Ars.  Rep.  1894,  p.  105.) 

stress-diagram  in  compression,  plotted  from  the  average  results  from  twenty- 
two  tests  of  gun-iron.  As  these  were  made  on  specimens  10.5  inches  long, 
having  a  sectional  area  of  1  sq.  in.,  they  all  failed  by  triple  flexure,  or  as 
columns,  at  an  average  value  of  63,000  pounds  per  square  inch,  the  actual 
crushing  strength  not  having  been  found.  (The  tensile  strength  averaged 
33,500  pounds  per  square  inch.) 

In  Fig.  388  are  shown  Bauschinger's  results  on  four  kinds  of  cast  iron, 
as  follows: 

No.  1  is  composed  wholly  of  coke  pig  iron. 
"     2  "         "  "       "   charcoal  pig  iron. 

"     3  "  90$  coke-pig  and  10$  steel. 
"     4  "  80$  coke-pig  and  20$  steel. 

The  tests  were  made  to  determine  the  time-effect  in  testing  cast  iron, 
there  being  two  specimens  of  each  kind  in  both  tension  and  compression, 
with  one  of  which  a  rest  of  one  minute  was  allowed  after  each  increment 
of  load,  and  with  the  other  a  rest  of  five  minutes.  No  time-effect  was 
discovered,  however,  and  here  the  mean'  curves  only  are  shown. 

In  all  these  cases  it  will  be  observed  that  no  well-marked  elastic  limit 
can  be  identified,  although  the  curves  are  plotted  to  a  very  large  scale  of 
deformations. 


474 


THE  MATERIALS  OF  CONSTRUCTION. 


FlG.  388.— Stress-diagrams  on  Four  Kinds  of  Cast  Iron.     Each  Curve  the  mean  of  two 
tests.    (Bauschinger's  Communications,  vol.  xx,  Plate  XII.) 


THE  STRENGTH  OF  CAST  IRON. 


475 


e00& 


£4000 


349.  The  Cross-breaking  Strength  of  Cast  Iron  is  in  general  from  one 
and  one  half  to  two  and  a  quarter  times  its  strength  in  tension  on  solid 
rectangular  sections.  The  cause  of  this  was  discussed  in  Chapter  V.  In 
Fig.  389  are  shown  autographic  stress- 
diagrams  of  four  kinds  of  cast  iron 
made  on  Keep's  standard  test-bars 
-J-  in.  square  and  12  in.  long.  They  all 
showed  the  same  strength  of  450  Ibs. 
at  the  centre,  giving  a  computed  mod- 
ulus of  rupture  of  64,800  pounds  per 
square  inch.  It  will  be  noted  that 
their  deformations  under  like  loads 
are  very  different,  thus  giving  rise  to 
enormous  differences  in  their  strength 
to  resist  shock.  Thus  their  resistances 
to  shock,  as  determined  by  the  total 
areas  of  their  stress-diagrams,  are  re- 
spectively 10.0,  21.5,  28.9,  and  35.1 
inch -pounds  per  cubic  inch.*  These 
four  tests  were  selected  to  show  the 
necessity  of  observing  the  deflections 
as  well  as  the  loads,  if  resistance  to 
shock  is  to  be  found.  These  diagrams 
also  show  that  no  great  error  is  made 
in  the  case  of  cast-iron  if  the  area  of 
the  stress-diagram  in  cross-bending 
be  assumed  to  be  equal  to  one  half  the 
product  of  the  breaking  load  into  the 
total  deflection.  This  is  the  common  FIG. 
rule  for  cast  iron.  This  half-product, 
divided  by  the  volume  or  weight  of 
the  specimen  between  the  supports, 
gives  the  shock-resisting  modulus  in 
inch-pounds  per  cubic  inch  or  per  pound  of  metal  as  the  case  may  be,  and 
is  independent  of  the  particular  dimensions  except  that  the  smaller  the  cross- 
section  the  greater  the  strength-modulus,  as  is  conclusively  shown  in  Keep's 
curves  in  Fig.  57,  p.  96.  Higher  shock-resisting  moduli  will  be  obtained, 
therefore,  on  small  (thin)  sections  than  on  large  ones,  and  the  only  safe 
rule  is  to  learn  by  trial  what  products  to  expect  and  to  demand  for  given 
sizes  of  test-specimens  and  given  grades  of  iron.  (See  Fig.  57,  p.  96.) 

The  committee  of  the  American  Society  of  Civil  Engineers  recommended 
(1896)  a  cross-breaking  test  of  cast  iron  in  which  /=  36,000  Ibs.  on  a  bar 


0          d/        0.2        A3 
389.— Cross-breaking     Autographic 

Stress-diagrams  of  Four  Kinds  of  Cast 

Iron  all  having  the  Same  Static  Strength. 

(Keep,  Tr.  Am.  Soc.  Mech.  Engrs.,  vol. 

xvn,  1896.) 


*  These  can  be  taken  out  per  pound  of  metal  if  preferred. 


476  THE  MATERIALS  OF  CONSTRUCTION. 

2  in.  by  1  in.  tested  flatwise  on  a  24-in.  base,  with  a  deflection  vof  0.3  in. 
This  corresponds  to  only  6£  inch-pounds  per  cubic  inqh. 

Mr.  Vf.  J.  Keep  has  shown  *  that  the  1-in.  square  bar  gives  more  uniform 
results  than  any  other  size,  because  at  this  size  the  effects  of  varying  per- 
centages of  silicon  are  not  appreciable,  as  is  shown  by  Fig.  57,  p.  96.  In 
reducing  the  great  number  of  tests  on  cast  iron  (some  500  in  all)  in  sizes 
from  4-  in.  square  to  4  in.  square  made  for  the  Committee  on  Methods  of 
Testing  Materials  of  the  American  Society  of  Mechanical  Engineers,  Prof. 
Benjamin  has  found  that  the  strength  of  all  sizes  of  cast-iron  bars  can  be 
related  to  that  of  the  1-in.  -square  bar  12  in.  long  by  the  following  formula:  f 

£0.83^1.89 
"     ~   *'    £1.058      >      .......         '        '         (1) 


where  W=  breaking  load  on  the  centre  of  the  bar; 

k  =  breaking  load  for  a  bar  1  in.  square  and  12  in.  long; 
1}  —  breadth  of  the  bar  in  inches; 
h  =  height  of  the  bar  in  inches; 

I  —  length  of  the  bar  in  feet  (multiples  of  12  in.,  which  is  the  length 
of  the  standard  bar.) 

The  theoretical  relation  is  W  =  h—~. 

L 

350.  The  Modulus  of  Elasticity  of  Cast  Iron  varies  quite  as  much  as  its 
strength.  In  this  respect  it  is  anomalous,  since  for  all  rolled  iron  and  steel 
the  modulus  of  elasticity  varies  only  about  five  per  cent  from  its  mean  value 
for  strength  variations,  in  the  case  of  steel,  of  several  hundred  per  cent. 
There  is  probably  a  pretty  definite  relation  between  the  strength  of  cast 
iron  and  its  modulus  of  elasticity,  the  stronger  iron  having  the  higher 
modulus  of  elasticity,  that  is,  it  is  stiffer.  At  least  this  relation  is  very  clearly 
shown  in  the  curves  in  Fig.  55,  p.  94.  In  general  this  modulus  varies  from 
10,000,000  to  30,000,000,  but  for  ordinary  foundry  iron  it  may  be  taken  at 
from  12,000,000  to  15,000,000,  or  about  one  half  that  of  wrought  iron  and 
rolled  steel. 

It  may  be  well  here  to  call  attention  again  to  a  ready  method  of  reading  the 
modulus  of  elasticity  from  any  of  the  tension-  or  compression-stress  diagrams 
given  in  this  book.  Where  the  loads  are  given  in  pounds  per  square  inch 
and  the  deformations  in  percentages,  or  proportionate  parts  of  the  length, 
then  by  observing  where  the  tangent  to  the  curve  at  the  origin  (or  the  curve 
itself  if  it  is  straight  so  far)  crosses  the  ordinate  which  marks  a  deformation 
of  0.001,  one  has  only  to  read  the  corresponding  stress  per  square  inch  and 
multiply  it  by  1000.  The  modulus  of  elasticity  of  cast  iron  is  approxi- 
mately the  same  in  tension,  in  compression,  and  in  cross-bending. 

*  Trans.  Am.  Soc.  MecJi.  Engrs.,  vol.  xvn.  (1896)  p.  681. 
f  Ibid  ,  p.  692. 


THE  STRENGTH  OF  CAST  IRON.  477 

351.  Kirkaldy's  Results.— In  Table  XXIV  are  given  the  results  of  469 
tests  of  cast  iron  in  each  of  the  three  ways,  tension,  compression,  and  cross- 
bending,  all  on  identical  material  in  each  case.     The  averages  of  all  are : 

Tensile  strength   25,000  Ibs.  per  square  inch 

Compressive  strength 121,000    "      "         "         " 

Cross-bending  modulus >...   38,000    "      "         "         " 

Quality-coefficient 6.5  in. -Ibs.  per  cubic  inch. 

The  mere  fact  that  these  specimens  were  submitted  to  Mr.  Kirkaldy  for 
testing  implies  that  the  mixtures  were  better  than  are  commonly  used  in 
foundry  practice,  and  yet  these  average  results  could  readily  be  reached  in 
any  good  foundry. 

The  small  ratio  of  the  cross-breaking  modulus  of  rupture  to  the  tensile 
strength,  this  having  an  average  value  of  but  1.52,  is  due  to  the  great  depth 
(2  in.)  of  the  transverse  test-bar.  The  small  value  of  the  "quality-coeffi- 
cient" is  doubtless  due  to  the  same  cause.  Otherwise  all  these  irons  would 
be  classed  as  comparatively  brittle. 

As  this  "  quality-coefficient"  was  not  taken  out  by  Kirkaldy,  and  as  it  is 
probable  that  only  breaking  strength  was  specified,  it  is  quite  probable  that 
high  strength  has  been  attained  in  this  material  at  the  expense  of  resilience 
or  shock-resistance.  The  ratio  of  the  cross-breaking  modulus  to  that  in 
tension  is  also  lower  with  less  flexibility.  The  modulus  of  elasticity  was  not 
computed  for  any  of  these  tests,  and  as  only  the  final  deflections  are  given 
in  the  published  report,  it  cannot  now  be  computed  from  the  tabular  matter. 

352.  Shrinkage  Stresses. — The  shrinkage  of  cast  iron  after  it  crystallizes 
is  so  great  that,  if  not  provided  for,  it  causes  excessive  deformations  which 
may  develop  very  great  stresses,  even  to  rupture.    The  heavier  or  the  thicker 
the  casting  the   greater  are  these  shrinkage  stresses.     These  have  been 
studied  in  the  case  of  cast-iron  guns,  and  one  such  analysis  is  shown  in  Fig. 
390.     Here  the  metal   was  over   11   inches  thick.     The  outer  and  inner 
surfaces  cooled  first,  and  the  subsequent  shrinkage  of  the  interior  put  these 
parts  in  compression.     But  since  the  total  internal  stress  across  any  diametral 
section  must  be  zero,  there  being  no  external  force  acting,  it  follows  that 
the  total  tensile  stress  must  equal  the  total  compressive  stress.     These  were 
all  found  directly  by  cutting  off  a  zone  included  between  two  transverse 
sections,  and  by  cutting  this  up  into  a  series  of  concentric  rings  as  shown  by 
the  dashed  lines  in  Fig.  390.     Before  cutting  these,  four  diameters  of  each 
ring  were  carefully  measured,  and  these  same  diameters  were  again  measured 
after  cutting  out.     An  increase  in  mean  diameter  indicated  an  initial  com- 
pression, and  vice  versa,  the  initial  stresses  being  found  from  the  equation 

f  =  UB, 

where/  =  stress  in  pounds  per  square  inch; 

A  =  proportionate  change  in  circumference; 
E  =  modulus  of  elasticity  of  the  material. 


478 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE   XXIV.— SUMMARY  OF  RESULTS   OF   TESTS  ON  CAST  IRON   IN   TENSION, 
COMPRESSION,  AND    CROSS-BENDING,  ON   IDENTICAL   MATERIAL. 

From  Kirkaldy's  Report,  1891  (Report  T  T). 


Total  Number  of  Tests  I 
from  One  Foundry. 

Grade. 

Tension  Strength  in  Pounds 
per  Square  Inch. 

Compression. 

Cross-bending. 

Strength  in  Pounds 
per  Square  Inch. 

Ultimate  Deforma- 
tion, Per  Cent. 

c  c  o> 
°'"  5 

co       3 

W   i-,   CT* 

gJoEf 

^£  £ 

•8    ? 

~  -^  . 

&2S.S 
fill 

o 

1 
8^ 

^  D 

"  o 

3 
0,  hH 

rt.2 

i 

*  Resistance  to  Shock 
or  "Quality-factor" 
in  Inch-pounds  per 
Cubie  Inch, 

151 
74 

Highest  ... 

32,821 
26,165 

141,632 
122,279 

6.65 
9  26 

47,710 
38,020 

25,820 

.32 
.27 

.21 

8.84 
5.94 

Mean          .  . 

Lowest  

16,250 

103,165 

12.20 

3.14 

Highest,  .  .  . 

27,614 
24,303 

124,251 
117,242 

37,390 
33,840 

.32 
.26 

6.22 
5  09 



Lowest    ... 

19,311 

109,682 

27,260 

.21 

3.31 

58 

Highest  

28,740 
24,148 

17,698 

131,912 
115,572 

13.30 
9.98 

4.45 

43,540 
39,550 

.40 
.36 

.33 

1.00 
8.24 

6.46 

Mean 

Lowest    

93/759 

33,840 

46 

Highest 

30,630 
23,339 

12,688 

137,165 
105.918 

11.80 
11.95 

46,460 
36,190 

.33 
.36 

8.87 
7.54 

Mean  

Lowest  

66,363 

12.70 

34,240 

.38 

5.33 

15 
15 

Highest  ...    

29  782 

138,496 
116,833 

10.40 
1066 

46,650 
44,460 

42,860 

.36 
35 

.32 

9.72 
899 

Mean  

22,727 

Lowest  

15  580 

83,307 

7.90 

7.94 

Highest  

26,040 
23.925 

132,857 
123,044 

36,100 
34,760 

31,360 

.28 
.26 

.24 

5.85 
5.22 

4.35 

Mean  

Lowest  



22,711 

113,233 

15 

Highest  

25,708 
23,129 

17,617 

123.531 
116,356 

9.20 
9  12 

7.35 

40,660 
39,700 

.36 
.36 

8.47 
8.27 

7.56 

Mean  

Lowest  

105,258 

38,400 

.34 

13 

Highest  

27,644 
24,321 

123,708 
116,538 

8.55 
8.64 

39.290 
32.780 

.39 
.29 

8.19 
5.50 

Mean  

Lowest  

19,188 

104,281 

7.00 

26,930 

.21 

3.27 

*  This   ' '  quality-coefficient 
area  of  the  stress-diagram  in 


"  is  a  measure  of  the  resistance  to  shock,  or  it  is  the 
inch-pounds  per  cubic  inch,  found  by  multiplying  the 


THE  STRENGTH  OF  CAST  IRON.  479 

SUMMARY    OF    RESULTS   OF  TESTS   ON   CAST   IRON — continued. 


Total  Number  of  Tests  1 
from  One  Foundry. 

Grade, 

Tension  Strength  in  Pounds 
per  Square  Inch. 

Compression. 

Cross-bending. 

Strength  in  Pounds 
per  Square  Inch. 

Ultimate  Deforma- 
tion, Per  Cent. 

Computed  Stress  on 
Outer  Fibre  in 
Pounds  per  Square 

| 

"o 

13      . 
<%$ 
0| 
H)M 

£.5 
5 

*Resistance  to  Shock 
or  ''Quality-factor" 
in  Inch-pounds  'per 
Cubic  Inch. 

13 

Highest      

26,502 
21,711 

16,090 

175,950 
123,336 

103,859 

4.05 
5.49 

6.45 

54,140 
40,750 

27,070 

36,050 
34,750 

31,870 

40,460 
38,020 

.45 
.34 

23 

14.10 
8,02 

3.60 

Lowest  

10 

Highest                      . 

25,176 
24298 

23,511 

127.988 
125,962 

120,874 

7.55 
7.03 

6.40 

.32 
.29 

.25 

6.68 
5.83 

4.61 

jVIeau                        . 

10 

Highest    

30,31(1 
29,268 

28,436 

136,266 
133,682 

12.25 
12.61 

.30 
.27 

.21 

7.02 
5.94 

4.14 

Lowest            

129,524 

13.90 

34,080 

10 
10 

Highest    

30,018 
29,472 

130,145 
127,714 

1210 
11  90 

39,  550 
38,400 

.34 
.32 

7.78  I 
7.11 

jVIean                   .  . 

27,501 

28,416 
27,763 

122,155 

11.75 

37,050 

1     .29 

6.22 

Highest 

140,542 
138,054 

6.60 
6.54 

38,780 
37,250 

.31 
.28 

6.96 
6.03 

Mean      

Lowest.  .  .  . 

26,851 

135,577 

6.60 

35,380         .27 

5.52 

10 

25  520 

127,703 
121,593 

7.80 
7.71 

34,960 
33,020. 

.  32 
.28 

.26 

6.46 
5.35 

4.54 

Mean  

24,803 

23,435 

Lowest  

110,405 

6.60 

30,190 

10 

Highest 

28,518 
27  914 

27,276 

129,603 
126,701 

124,415 

9.10 
9.70 

9.15 

40  370 
38,060 

35,470 

.35 
.32 

.26 

8.18 
7.05 

]\Ieau    

Lowest 

5.34 

g 

Hio-hest    ... 

33,616 
29,202 

143,939 
137,804 



46,990 
43,490 

.41 
.39 

11.15 
9.81 

Mean     

Lowest  

19,046 

124,410 

43,490 

.31 

6.82 

breaking  load  by  the  final  deflection  and  dividing  by  twice  the  volume  of  the  bar.  It 
was  not  computed  by  Kirkaldy.  All  these  bars  were  2  in.  x  1  in.  X  36  in.  long,  tested 
edgewise,  the  tension  and  compression  specimens  being  cast  on  the  same  pattern.  The 
great  depth  of  these  bars  makes  this  quality-factor  and  also  the  modulus  of  rupture  run 
low  as  compared  to  tests  on  thinner  specimens. 


480 


THE  MATERIALS  OF  CONSTRUCTION. 


In  this  way  the  stress-diagrams  shown  in  Fig.  390  were  computed  and 
drawn  by  the  author  from  the  data  furnished  in  the  original  report.  It 
indicates  that  the  interior  surface  was  under  an  initial  compressive  stress  of 
some  7000  Ibs.  per  square  inch,  the  outer  surface  of  some  13,500  Ibs.  per 
square  inch ;  while  the  interior  was  under  a  tensile  stress  of  some  2000  Ibs. 
pei-  square  inch.  Evidently  the  tension  and  compression  areas  on  these 
diagrams  must  equal  each  other.  This  is  a  very  simple  illustration  of  such 
shrinkage  stresses,  because  of  its  simple  and  symmetrical  form.  In  complex 
forms  it  would  be  impossible  to  study  or  predict  the  character  of  these 


FIG.  390. — Showing  the  Shrinkage  Stresses  in  Cast-iron  Cannon  11  in.  thick. 

(Wat.  Are.  Rep.) 

stresses.     They  are  evidently  less  when  all  parts  are  made  of  approximately 
the  same  thickness. 

353.  Strength  of  Cast  Iron  Increased  by  Shocks. — Mr.  A.  E.  Outerbridge 
has  shown*  that  castings  which  have  been  subjected  to  a  great  number  of 
shocks  or  blows  are  from  10  to  15  per  cent  stronger  under  a  static  load  and 
over  20  per  cent  stronger  under  impact  than  they  are  before  receiving  such 
treatment.     He  attributes  this  result  to  a  sort  of  molecular  rearrangement 
by  which  the  cooling  stresses  are  relieved.     In  other  words,  such  treatment 
is  equivalent  to  an  annealing  process. — This  is  probably  a  general  fact  and 
true  for  all  kinds  of  castings,  although  this  remains  to  be  proved. 

354.  Strength  of  Malleable  Cast  Iron. — For  the  experimental  results  of 
tests  of  the  strength  of  malleable  cast  iron  see  Art.  82,  p.  114. 

355.  Cast-iron  Pipes  and  Columns. —  In  estimating  the  actual  strength  of 
cast-iron  pipes  subjected  to  internal  pressure,  a  great  source  of  uncertainty 

*  Trans.  Am.  Inst.  Mm.  Engrs.,  Pittsburg  Meeting,  1896. 


THE  STRENGTH  OF  CAST  IRON.  481 

lies  in  the  probable  unequal  thickness  of  the  metal  in  the  upper  and  lower 
sides  when  cast.  There  is  a  great  tendency  of  the  core  to  rise  from  the 
buoyancy  of  the  liquid  iron,  and  since  no  core,  however  strong,  can  be  abso- 
lutely rigid,  it  must  be  assumed  that  it  does  always  lift  somewhat  at  the 
centre,  however  strongly  it  is  held  at  the  ends.  As  a  matter  of  fact,  the 
cores  are  not  usually  very  rigid,  so  that  such  pipeL  are  apt  to  be  very  unequal 
in  thickness  on  the  opposite  sides,  as  shown  in  Fig.  391.  The  regular  bell- 
and-spigot  water-  and  gas-pipes  are  now  all  cast  vertically,  and  hence  this 


FIG.  391.— Actual  Section  of  an  8-iu.  Cast-iron  Steam-pipe.     (From  The  Locomotive, 

Oct.,  1896.) 

danger  is  largely  obviated,  but  flange-pipes,  such  as  are*  used  for  steam 
purposes,  are  cast  horizontally.  Any  great  inequality  in  thickness  can  be 
found  by  rolling  the  pipe  down  inclined  ways  and  noting  the  irregularity 
of  motion 

Cast-iron  columns,  such  as  are  used  in  buildings,  are  also  cast  horizon- 
tally, and  are  subject  to  this  same  contingency.  These  may  be  bored  to 
determine  thickness,  but  pipes  cannot  be  examined  in  this  way.  It  is  such 
undiscoverable  faults  as  this  which  form  the  greatest  objection  to  the  use  of 
cast  iron  for  these  purposes.  For  other  defects  in  cast-iron  columns  see 
Plate  III. 


CHAPTEK  XXV. 
THE  STRENGTH   OF  WROUGHT  IRON. 

356.  The  Tensile  Strength  of  wrought  iron  along  the  grain  varies  from 
45,000  to  55,000  pounds  per  square  inch.     It  is  greater  in  small  rods  and 
thin  plates  than  in  large  bars  and  thick  plates,  the  material  remaining 
the  same.    .This  is  shown  in  Fig.  392,  where  the  same  material  has  been 
rolled  into  bars  from  f  in.  to  2  in.  in  diameter,  the  tensile  strength  varying 
from  52,000  in  the  smaller  to  47,500  pounds  per  square  inch  in  the  larger 
sizes. 

The  Elastic  Limit  is  more  dependent  on  the  thinness  of  the  final 
section  than  on  the  tensile  strength,  as  is  well  brought  out  in  Fig.  392.  Here 
the  apparent  elastic  limit  varies  from  40,000  pounds  per  square  inch  in  the 
f-in.  rods  to  23,000  pounds  per  square  inch  in  the  2-in.  rods,  and  is  almost 
identical  with  the  "yield-point."  This  increase  in  the  elastic  limit  with 
increased  reduction  in  the  rolls  ahv'ays  occurs  with  both  wrought  iron  and 
steel,  but  it  is  much  more  pronounced  with  wrought  iron.  The  true  elastic 
limit  of  wrought  iron  is  nearly  always  much  lower  than  the  apparent 
elastic  limit.  In  Fig.  392  it  is  found  from  5000  to  7000  Ibs.  lower  in  every 
case.  In  mild  steel  these  two  limits  are  almost  identical. 

The  Percentage  of  Elongation  in  8  in.  varies  from  5$  to  25$  when  tested 
in  the  direction  of  the  fibres,  depending  on  the  quality  of  the  material,  the 
reduction  of  area  averaging  about  50^  more  than  the  elongation.  The  elon- 
gations recorded  in  Fig.  392  were  all  taken  on  a  length  of  20  in.,  which 
somewhat  reduces  the  percentage,  especially  for  the  smaller  sections. 

357.  The  Tensile  Strength  across  the  Grain  is  always  much  less  than 
along  the  grain  in  the  case  of  wrought  iron,  while  with  steel  there  is  no 
appreciable  difference.     Very  few  tests  of  wrought  iron  across  the  fibres 
are  to  be  found  on  record,  but  the  author  has  often  observed  in  his  own 
practice  that  it  is  very  much  less  in  this  direction  than  parallel  to   the 
direction  of  rolling.     In  Prof.  Bauschinger's  Communications,  vol.  n,  we 
find  an  elaborate  study  of  this  subject  on  wrought-iron  boiler-plates  from 
eight  different  sources,  some  of  them  having  been  taken  from  boilers  which 
had  exploded.     From  this  report  we  have — 

1.  From  eight  tensile  tests  along  and  eight  across  the  grain,  from  an 
exploded  boiler,  the  ratio  of  lateral  to  longitudinal  strength  was  0.74. 

482 


THE  STRENGTH  OF  WROUGHI  IRON.  483 

.  From  a  wrought-iron  plate  from  another  exploded  boiler  eight  test- 


FIG.  392. — Stress-diagrams  (in  tension)  of  Wrought-iron  Bars  of  varying  Diameters, 
all  rolled  from  the  same  Material.  All  Elongations  measured  on  a  Length  of  20  in. 
The  "  Apparent  Elastic  Limit  "  falls  from  2#  to  10#  lower  than  the  indicated  "Elas- 
tic Limit  "  in  the  original  Report ;  it  varies  from  23,000  in  tbe  2-in.  to  40,000  Ibs.  in 
the  3-in.  specimens  ;  and  it  marks  a  point  where  the  permanent  set  is  less  than  0.0001 
of  the  length  of  the  specimen.  Each  diagram  is  the  average  of  from  3  to  6  tests. 
(Wat.  Ars.  Rep.  1888.) 

specimens  were  cut  in  each  direction,  giving  a  mean  ratio  of  lateral  to 

longitudinal  strength  of  0.71. 


484  THE  MATERIALS  OF  CONSTRUCTION. 

3.  On  six  other  new  plates  from  as  many  different  sources  he  obtained 
ratios  of  0.76,  0.62,  0.92,  0.90,  0.76,  and  0.83. 

The  average  value  of  all  these  is  0.78. 

In  short,  we  may  fairly  affirm  that  the  ultimate  tensile  strength  of 
wrought  iron  transverse  to  the  direction  of  the  rolling  is  only  about  three 
fourths  of  its  strength  parallel  to  this  direction.* 

The  author  is  credibly  informed  that  the  best  English  Yorkshire 
(Lowmoor)  iron  plates  are  always  rolled  from  "puddled  lumps"  12  in. 
square,  which  correspond  to  muck-bars,  these  being  piled  so  as  to  cross 
their  grain,  and  in  this  way  the  final  plates  are  nearly  as  strong  transversely 
as  they  are  longitudinally.  It  is  claimed  that  for  an  ultimate  strength  of 
51,500  pounds  per  square  inch,  with  an  elongation  of  16$  longitudinally, 
it  shows  an  ultimate  strength  of  45,000  pounds  per  square  inch  and  an 
elongation  of  12$  transversely.  As  this  material  costs  about  four  times 
as  much  as  the  best  mild-steel  plates,  its  use  for  all  purposes  where  forging 
and  welding  are  not  required  is  rapidly  declining. 

358.  Tensile  Strength  of  Wrought  Iron  as  Affected  by  Pulling  Speed  and 
by  Length  of  Reduced  Section. — In  Table  XXV  are  given  the  results  of  a 
series  of  very  careful  tests  to  determine  the  effects  of  speed  and  of  the  length 
of  the  reduced  section  on  the  tensile  strength  of  wrought  iron.     It  will  be 
observed  that  the  ultimate  strength  is  somewhat  increased  by  very  rapid 
testing,  while  the  elongation  and  reduction  are  not  appreciably  affected  by 
this  average  range  of  speed  from  15  sec.  to  8.5  min.     The  strength  is  also 
much  greater  for  very  short  reduced  sections  than  for  longer  ones.    Similar 
results  on  steel  bars  are  shown  in  Fig.  426. 

359.  The  Compressive  Strength  of  Wrought  Iron,  like  that  of  any  of  the 
ductile  metals,  must  be  regarded  as  the  "apparent  elastic  limit"  or  "yield- 
point."     Here  the  material  buckles  out  of  shape,  and  if  the  specimen  has 
appreciable  length,  failure  at  once  follows.     If  this  be  allowed,  then  it  may 
be  seen  at  once,  from  Fig.  392,  that  the  same  puddle-ball,  rolled  to  different 
sections,  will  show  compressive  strengths  anywhere  from  26,000  to  40,000 
Ibs.  per  square  inch.    Since  wrought-iron  columns  are  built  up  of  structural 
forms  which  have  been  rolled  to  thin  sections,  from  J-  to  f  in.  in  thickness, 
it  follows  that  such  material  will  have  a  "yield-point"  or  "apparent  elastic 
limit "  of  from  30,000  to  40,000  Ibs.  per  square  inch.    Since,  also,  the  amount 
of  reduction  in  the  rolls  has  a  less  effect  on  the  elastic  limit  of  mild  steel,  it 
follows    that    the  yield-point,  and   hence  the  compressive  strength,  of  a 
wrought-iron  column  may  be  about  equal  to  that  of  a  steel  member  built 
up  of  similar  sections,  although  the  ultimate  strength  of  tne  steel  in  tension 
may  be  25  per  cent  higher  than  that  of  the  wrought  iron.     This  variation 
of  the  compressive  strength  (yield-point)  of  wrougnt-iron  columns  with  the 

*  The  author  has  been  unable  to  find  the  data  for  plotting  a  stress-diagram  of 
wrought  iron  across  the  grain. 


THE  STRENGTH  OF   WROUGHT  IRON. 


485 


TABLE    XXV.— TESTS    OF    WROUGHT    IRON     TO     SHOW     EFFECT   OF     SLOW   AND 
OF    RAPID    FRACTURES   ON    SPECIMENS    OF   VARYING    LENGTH. 

Sixteen  specimens  taken  from  the  same  bar  of  iron  If  in.  square,  all  reduced  to  a 
diameter  of  1.008  in.  or  to  a  sectional  area  of  0.80  sq.  in.  Specimens  marked  f rom  A 
to  P  consecutively,  as  cut  from  the  bar.  (From  U.  S.  Wat.  Ars.  Rep.  1887,  p.  924.) 


Marks. 

Length. 

Elastic 
Limit  per 
Square  Inch. 

Ultimate 
Strength 
pei- 
Square  Inch. 

Duration 
of 
Test. 

Gauged 
Length. 

Elonga- 
tion in 
Gauged 
Length. 

Contrac- 
tion. 

Final  Load 
per 
Square  Inch 
on  Rup- 
tured Sec- 
tion. 

Inches. 

Pounds. 

Pounds. 

Inches. 

Per  cent. 

Per  cent. 

Pounds. 

A 

Grooved          .... 

57,200 

6  miu. 

32.4 

72,090 

B 

Grooved 

59,250 

6  sec. 

32.4 

. 

C 

0.80 

27',  375 

49,380 

6  uiin. 

49.1 

71,260 

D 

0.80 

.... 

50,750 

8  sec. 

37.1 

.... 

E 

1.60 

28',  500 

47,730 

10  min. 

1 

56.0 

47.6 

78,280 

F 

1.60 

.... 

49,130 

13  sec. 

1 

50.0 

46.2 

§ 

G 

2.40 

80,125 

47.980 

8  min. 

2 

39.0 

43.2 

81,680 

H 

2.40 

49.000 

14  sec. 

2 

41.5 

49.1 

I 

3.20 

29,625 

47,070 

10  min 

3 

39  .  0 

49.1 

77,150 

J 

3.20 

.... 

48,120 

15  sec. 

3 

36.0 

47.6 

.... 

K 

4.80 

29,875 

46,860 

10  miu 

4 

32.0 

43.2 

70,260 

L 

4.80 

48,000 

18  sec. 

4 

32  8 

47.6 

M 

6.40 

29,750 

47,450 

9  miu. 

6 

25.0 

49.1 

80,590 

N 

6.40 

48,250 

20  sec. 

6 

32.0 

47.6 

.... 

0 

8.00 

28.500 

45,650 

9  miu. 

8 

25.9 

41.7 

66,950 

P 

8.00 

.... 

46,000 

30  sec. 

8 

25.9 

41.7 

.... 

Mean  of  slow  tests  = 

48,670 

8.5  miu. 

36.1 

44.4 

73,500 

3Iean  of  quick  tests  = 

49,810 

15.5  sec. 

d6.4 

43.7 



thickness  of  the  sections  of  which  the  member  is  composed  accounts  for  a 
large  portion  of  the  disc^emncies  found  in  the  results  of  tests  on  wrought- 
iron  coiiimns  in  commercial  sizes  (see  Fig.  297,  p.  364).  Thus  Tetmajer 
found  for  short  columns  composed  of  four  angle-irons,  2.4  in.  X  2.4  in.  X 
-]  in.  in  thickness,  me  average  strength  of  the  wrought-iron  columns  was 
38,000  Ibs.  per  square  men  of  net  section,  while  that  of  similar  mild-steel 
columns  was  but  36,000  Ibs.  per  square  inch.  The  ultimate  tensile  strength 
of  the  wrought  iron  was  50,000  Ibs.  per  square  inch,  while  that  of  the 
steel  was  61,000  Ibs.  per  square  inch.  With  angles  0.4  in.  thick  the  steel 
columns  had  an  ultimate  strength  of  37,"500  Ibs.  per  square  inch,  while  the 
wrought-iron  columns  showed  only  32,300  Ibs.*  With  sections  •§  in.  thick 
and  less,  therefore,  there  is  probably  little  difference  between  the  strength  of 
wrought-iron  and  soft-steel  columns. 

360.  The  Shearing  Strength  of  Wrought  Iron.  —  The  most  elaborate 
investigation  ever  made  on  wrought  iron,  so  far  as  the  author  is  aware,  was 
that  made  by  Bauschinger  and  reported  in  vol.  n  of  his  Communications. 
He  made  several  hundred  tests  of  the  shearing  strength  of  wrought-iron 
plates  from  seven  different  sources,  finding  the  shearing  resistance  in  two 


*  Communications,  vol.  iv.  pp.  141,  149,  and  155. 


486 


THE  MATERIALS  OF  CONSTRUCTION. 


directions  on  each  of  the  three  of  the  principal  planes,  as  shown  in  Fig.  393. 
As  there  was  a  general  agreement  in  the  relative  strength  on  these  planes,  only 
the  averages  of  a  portion  of  the  tests  are  given  in  the  diagram.  In  general, 
we  may  say  that  the  shearing  strength  across  the  thickness  of  the  plate,  either 
with  or  across  the  grain,  is  about  80  per  cent  of  the  tensile  strength,  while 
if  the  external  forces  lie  in  the  plane  of  the  plate,  and  be  applied  on  the 


j.        JLL       MI      At       y 

FIG.  393.— Shearing  Strength  of  Wrought  Iron  on  the  Six  Principal  Planes,  as  compared 
to  its  Tensile  Strength.  The  numbers  indicate  the  number  of  results  averaged. 
The  direction  of  rolling  is  indicated  by  the  large  arrow.  (Bauschinger's  Communi- 
cations, vol.  ii.) 

planes  of  shear  perpendicular  to  the  plane  of  the  plate,  the  shearing  strength 
is  about  the  same  as  the  tensile  strength.  The  shearing  resistance  on  a 
plane  parallel  to  the  plane  of  the  plate  is  less  than  45  per  cent  of  the  tensile 
strength. 

361.  The  Effects  of  Stressing  Wrought  Iron  beyond  its  Elastic  Limit  is  to 
raise  this  limit,  and  also  to  greatly  increase  the  ultimate  strength  after  a 
period  of  rest.  Thus  in  Fig.  394  are  shown  the  results  of  tests  on  three 
wrought-iron  bars  3  in.  X  1  in.  Here  the  apparent  elastic  limit  on  the 
second  test  (computed  on  the  original  cross-section)  is  much  greater  than 
the  original  ultimate  strength,  and  almost  equal  to  the  ultimate  strength  on 


THE  STRENGTH  OF   WROUGHT  IRON. 


487 


flff/ 


FIG.  394.—  Wrought-irou  Bars,  3  in.  by  1  in.  retested,  First  test  gave  El.  lim.  =  30,000; 
ult.  str.  =  53,700;  %  elong.  =  16  on  100  in.  Ends  of  broken  bars  retested  and  loads 
computed  per  sq.  in.  of  original  section.  Second  Elongation  taken  on  50  in.  and  per 
cent  elongation  computed  on  the  new  gauged  length.  (Rep.  Wat.  Ars.  1882.) 


30 


SO 


W9/W 


//V  61W 


rf- 


FIG.  395.— Increase  in  the  Tensile  Strength  of  Wrought  Iron  after  having  been  Stressed 
to  the  Tensile  Limit.  Points  plotted  are  averages  from  5  to  15  tests  each.  (Rtp. 
U.  S.  Test  Board,  1881,  vol.  i.  pp.  Ill  and  115.) 


488 


THE  MATERIALS  OF  CONSTRUCTION. 


the  second  test.  After  annealing,  however,  the  material  snowed  a  much 
lower  elastic  limit  and  ultimate  strength  than  it  had  before  it  was  stressed 
at  all.  Stretching  the  material  somewhat  beyond  the  elastic  limit,  but  not 
to  failure,  would  show  less  marked  results.  If  little  or  no  time  is  allowed 
to  elapse  between  the  tests,  there  is  no  permanent  increase  in  the  strength, 
but  the  rate  of  increase  in  strength  with  time  after  stretching  to  its  tensile 
limit  is  well  shown  in  Fig.  395. 

When  any  ductile  metal  is  stressed  beyond  its  normal  elastic  limit  in 
either  tension  or  compression  it  loses  its  perfect  elasticity  under  the  opposite 
kind  of  stress.  Thus  for  wrought  iron,  Fig.  396,  has  been  constructed  by 


~80jOOO\ 


FIG.  396.— Showing  that  a  small  Permanent  Set  of  Wrought  Iron  from  either  Ten- 
sion or  Compression  greatly  reduces  the  Elastic  Limit  under  the  Opposite  Stress. 
(Gray,  in  The  Digest  of  Physical  Tests,  vol.  i.  p.  232  (1896).) 

plotting  consecutively  a  series  of  autographic  diagrams  taken  by  Prof.  Gray.* 
Although  at  first  the  permanent  set  given  to  the  specimen  in  tension  was 
less  than  one  per  cent  of  its  length,  yet  when  this  was  relieved  and  a  com- 
pressive  stress  applied  it  was  shown  that  the  specimen  was  no  longer  per- 
fectly elastic  in  compression,  but  gave  a  continuously  curving  stress-dia- 
gram. It  was  then  compressed  back  to  its  original  length,  and  a  tensile 
stress  applied,  when  it  was  found  to  be  no  longer  perfectly  elastic  in  tension. 
It  was  now  permanently  elongated  about  one  per  cent  of  its  length,  and  the 
load  removed  and  again  imposed,  and  it  was  found  that  the  specimen  was 
now  perfectly  elastic  in  tension  up  to  the  limit  of  its  previous  loading  and 
somewhat  higher,  but  when  it  was  now  elongated  18  per  cent  it  was  no 


*  Reported  in  The  Digest  of  Physical  Tests,  vol.  i.  p.  206. 


THE  STRENGTH  OF   WROUGHT  IRON. 


489 


longer  perfectly  ela'stic  in  either  tension  or  compression.     Similar  results 
are  shown  on  steel  in  Figs.  43G  and  437. 

362.  The  Strength  of  Wrought-iron  Chains.— The  hundreds  of  tests  on 
wrought-iron  chains  given  in  the  Report 
of  the  U.  S.  Test  Board,  1881,  vol.  i, 
show  that  the  ultimate  strength  of 
chains  may  be  taken  at  1.6  that  of  the 
iron  from  which  the  links  are  made.  It 
also  appears  from  these  tests  that  open 
links  are  somewhat  stronger  than  studded 
links,  though  the  open-link  chains  take 
a  permanent  set  earlier  than  the  studded 
links.  It  is  thought,  however,  that  open- 
link  cables  would  foul  more  readily  than 
the  studded  cables.  The  elastic  proper- 
ties of  open-link  chains  made  of  1-in. 
and  -J-in.  iron  are  shown  in  Fig.  397, 
where  the  tests  have  been  carried  to  the 
proof -load  only,  this  being  such  as  to 
give  to  the  chains  a  permanent  set  of 


>     i 


about  two  per  cent  of  their  length.  They  FIG  397-_Proof  Tests  of  Cbajus  with 
now  become  perfectly  elastic  to  20,000  Open  Liuks<  Tbe  118_in  chain 
and  15,000  Ibs.  respectively,  and  are  also 
about  five  times  more  stiff,  or  rigid,  than 
they  were  at  first.  All  chains  are  im- 
proved by  this  treatment,  while  it  also  discovers  any  very  poor  welds  the 
chain  may  have. 


made  of  1-in.  iron,  and  the  90-in. 
chain  of  f-in.  iron.  (Wat.  Ars. 
Rep.  1894.) 


CHAPTER   XXVI. 
THE   STRENGTH  OF   STEEL. 


356.  The  Tensile  and  the  Compressive  Strength  of  Steel  of  various  per- 
centages of  carbon  are  well  shown  in  Figs.  399  to  404.*     A  study  of  these 


...- 


-1 


Y 


Aff0)t0ftT/{M//i7'£ 


MS 
000S 


0./0 
00/0 


\ 


f/cfc 


FIG.  398.—  Compression  and  Tension  Tests  on  Midvale  Steel  Bars.  Compression  tests 
on  bars  1  in.  diam.  and  5  in.  long,  tension  tests  on  bars  0.56  in.  diam.  and  5  in.  long. 
(Wat.  Ars.  Rep.  1889.) 

*  In  all  these  figures  the  loads  are  given  in  pounds  per  square  inch,  though  this  is  not 
always  so  stated.  ' 

490 


THE  STRENGTH  OF  STEEL. 


^ 


" 


::, 


,•:• 


V  /Y/ 


0 


/7/7 


V//? 

// 1/ 


03, 


.02  .04 


7 


;t 


> 


-cc 


L 


7/c 


7 C 


'7% 


V 


.02  .04  .06  .08 


"          .00/         .002  ^  ,00/         .002         .003 

FIG.  399.— Compression  and  Tension  Stress-diagrams  of  Steel  Bars  of  Varying  Percentages 
of  Carbon.     Compression  specimens  12  in.  long  and  1  in.  in  diam.j-  =  33\  with  flat 

ends.  Tension  specimens  same  diam.  with  a  gauged  Length  of  30  in.  All  speci- 
mens turned  from  open-hearth  steel  bars  1±  in.  in  diam.  (  Wat.  Ars.  Rep  1886  and 
1887.) 


492 


TEE  MATERIALS  OF  CONSTRUCTION. 


figures,  all  of  which  are  typical  and  characteristic,  will  lead  to  the  following 
conclusions: 


4400 


60000 


40000 


Ea 


N 


04 


& f. 


FfiL 


w 


1 


7" 


^ 


/7  / 


0.4? 


/v 


.02 
.00/ 
FIG.  400.— Steel  Tests  supplemeiilary  to  those  of  Fig.  399. 

1.  The  tensile  strength  varies  from  55,000  Ibs.  for  0.1  per  cent  carbon 
to  150,000  Ibs.  per  square  inch  for  1.0  per  cent  carbon. 


THE  STRENGTH  OF  STEEL. 


493 


2.  The  "  apparent  elastic  limit  "  is  found  between  60  and  70  per  cent 
of  the  ultimate  strength. 

3.  The  "  apparent  elastic  limit  "  in  compression  is  practically  the  same 
as  that  in  tension. 


FIG.  401. — Tension  Stress-diagrams  of  Gautier  Steel  Bars  which  were  used  in  the  En- 
durance Tests  on  Rotating  Shafting  subjected  to  Reversals  of  Stress.  Percentages 
of  carbon  and  areas  of  the  stress-diagrams  in  square  inches  are  given  on  the  curves. 
(Rep.  Wat.  Ars.  1894.) 

4.  The  modulus  of  elasticity  in  compression  is  slightly  greater  than  that 
in  tension,  and  in  both  cases  it  is  practically  independent  of  the  percentage 
of  carbon  and  of  the  ultimate  strength. 

5.  The    ultimate   strength    in    compression  is  practically  equal  to   the 
"  apparent  elastic  limit  "  (Fig.  294,  p.  360). 


494 


THE  MATERIALS  OF  CONSTRUCTION. 


6.  In  the  mild  and  medium  steels  (carbon  0.2  to  0.6  per  cent)  there  is 
a  very  decided  drop  in  the  stress-diagram  after  reaching  the  "apparent 
elastic  limit  "  often  as  much  as  5000  or  6000  Ibs.  per  square  inch. 


FIG.  402. — Tension  Stress-diagrams  (incomplete)  of  Steel  Bars  used  for  Endurance 
Tests  of  Rotating  Shafting.  Average  product  of  ultimate  strength  by  percentage 
of  elongation  is  2,180,000.  (Wat.  Ars.  Reps.  1889  and  1891.) 

7.  The  coefficient  of  expansion  decreases  with  the  increase  in  carbon,  its 
average  value  being  about  0.0000065  per  degree  F.  (Fig.  294). 

8.  The   high   carbon-steels   are  greatly  softened,    the   tensile   strength 
lowered,  and  the  ductility  increased  by  annealing  (Fig.  404). 


THE  STRENGTH  OF  STEEL. 


495 


357.  The  Effect  of  Thickness  on  the  Mechanical  Properties  of  Structural 
Steel. — In  Figs.  400,  407,  and  408  are  shown  the  effect  of  thickness  (bars 
and  angles)  on  the  mechanical  properties  of  structural  steel.  Thus  from 


.02 


FIG.  403.—  Tension  Tests  of  Steel  Bars  used  for  Endurance  Tests  of  Rotating  Shafting. 
(Wat.  Ars.  Rep.  1889  and  1891.     Supplementary  to  Fig.  402.) 

Fig.  40G,  where  the  thickness  ranges  by  eighths  of  an  inch  from  f  to  J  inch, 
we  may  see — 

1.  The  ultimate  strength  is  nearly  constant, 

2.  The  apparent  elastic  limit  varies  from  41,000  at  f  to  37,800  Ibs.  per 
square  inch  at  the  f-in.  thickness. 


496 


THE  MATERIALS  OF  CONSTRUCTION. 


/77 


FIG.  404.— Tension  Stress-diagrams  of  Three  Grades  of  High-carbon  steel.    (Wat.  Ars. 

Rep.  1894.) 


mo. 


20.000 


7 


WVRT/MATl 


0          JO          .20         .30 

FIG.  405. — Autographic  Stress-diagram  of 
Rivet-steel  in  "Tension,  showing  Effect 
of  Removing  the  Load.  (M.  Dupuy,  in 
An.  d.  Fonts  et  Chaussees,  PI.  I.  1895.) 


FIG.  406.— Effect  of  Thickness  on  the 
Mechanical  Properties  of  Acid  Open- 
hearth  Steel  Angles.  (Campbell's 
Structural  Steel,  p.  202.) 


THE  STRENGTH  OF  STEEL. 


497 


3.  The  percentage  of  elongation  in  8  in.  is  nearly  constant. 

4.  The  reduction  of  area  varies  from  58  per  cent  at  f  in.  to  50  per  cent 
at  I  in.  thickness. 

Elastic  limit 
.0.   Ihe  elastic  ntio:    Ultimate  strength  vanes  from  68  per  cent  at  f  in. 

to  01.5  per  cent  at  -|  in.  thickness. 


emo 


wooo 


JWOO 


7m. 


-f 

& 


^ 

s 


60.000 


40        50.000 


20       30,000 


flV/VM 


0M 


OAAM&L 


3 


30 


20 


FIG.  408.— Effects  of  Thickness  on  Bessemer  Steel 
Angles.  Each  point  is  the  mean  of  fifty  re- 
sults. (Campbell's  Structural  Steel,  p.  199.) 


FIG.  407.— Effect  of  Thickness  on 
the  Mechanical  Properties  of  Mild 
Steel,  Natural  and  Annealed. 
(Campbell's  Structural  Steel.} 

From  Fig.  409  it  may  be  seen  that  the  variation  in  ultimate  strength  and 
in  the  elastic  limit  for  different  thicknesses  is  much  greater  when  the  metal 
leaves  the  rolls  at  a  dull-red  heat.  Here  the  thickness  ranges  from  ^  in.  to 
|  in.,  and  the  elastic  limit  for  normal  rolling  varies  from  about  50,000  Ibs. 
per  square  inch  at  the  ^-in.  thickness  to  39,000  Ibs.  at  a  f-in.  thickness. 
When  leaving  the  rolls  at  a  dull-red  heat,  however,  the  elastic  limit  for  the 
£-in.  thickness  was  57,500  Ibs.,  while  for  the  f-in.  thickness  it  was  only 
42,000  Ibs.  per  square  inch. 

In  general  the  apparent  elastic  limit  rises  as  the  thickness  of  section 
diminishes.  Since  wrought-iron  and  steel  columns  are  built  up  from  com- 
paratively thin  sections  of  metal  (generally  from  ^  to  i  in.  in  thickness),  and 
as  the  ultimate  strength  of  these  is  dependent  wholly  on  the  apparent  elastic 
limit,  and  not  at  all  on  the  ultimate  strength,  it  is  necessary  to  evaluate  this 
elastic  limit  for  the  particular  thicknesses  of  sections  useda  rather  than  from 


498 


THE  MATERIALS  OF  CONSTRUCTION. 


7Q000 i 


6MOO 


40000 


r* 

CT       !    "^ 


BAR 


70000 


60030 


50000 


3DOOO 


20000 


8& 


70 


60 


50 


4-0 


50 


fe*      %  ABA  BAB 

FIG.  409.  FIG.  410. 

FIG.  409. — Influence  of  Thickness  on  Mechanical  Properties    when  the  Percentage  of 
Reduction  iii  Rolling  is  constant,  and  when  the  Last  Passage  in  the  Rolls  was  at  the 
Normal  and  at  a  Dull  Red  Heat  respectively.     (Campbell's  Structural  Steel.} 
FIG.  410.— Showing  the  Effect  of  finishing  Three  Grades  of  Open-hearth  Steel  Bars  at  a 
Low  Red  Heat.     (Campbell's  Structural  Steel,  Table  70.) 


70000 


60.000\ 


3QOOO 


?oono 


50 


*J 


30 


20 


/V  A  /V  AN  AN 

FIG.  411.— Showing  Effect  of  Annealing  Open-hearth  Steel  Bars  2in.  X%  in.  when 
Rolled  Originally  at  a  Normal  and  at  a  Low  Red  Heat.  (Campbell's  Structural  Steel, 
p.  213.) 


THE  STRENGTH  OF  STEEL. 


499 


special  test-bars,  which  are  usually  not  less  than  f  in.  in  thickness.  (See 
Table  XXV,  p.  503.  for  the  comparison  between  the  results  obtained  on  the 
preliminary  f-in.  billet  test-specimen  and  those  from  the  specimens  cut  from 
rolled  bars  and  plates  of  various  thicknesses  from  the  same  ingot.) 

The  comparatively  small  variation  in  the  elastic  limit  (and  other  proper- 
ties) shown  in  Fig.  408  is  due  to  the  fact  that  all  were  rolled  from  the  same 
sized  ingot,  and  thus  the  thinner  sections  had  more  work  done  upon  them. 
When  the  proportionate  reductions  are  the  same  in  each  case  the  differences 
are  very  much  greater,  as  shown  in  Fig.  409.  These  differences  almost 
wholly  disappear  on  annealing,  as  shown  by  Fig.  407. 

358.  Effects  of  Finishing  at  a  Low  Red  Heat. — As  shown  by  Figs.  409 
and  410,  the  effect  of  finishing  at  a  low  red  heat  is  to  somewhat  increase 
the  ultimate  strength  and  the  elongation,  and  to  greatly  increase  the  elastic 
limit.  This  last  increase  is  as  much  as  from  8  to  10  per  cent.  From  Fig. 
411  it  appears  that  while  annealing  lowers  both  ultimate  strength  and  elastic 

08 


0.6 


05 


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. 

1 

• 

1 

.  ' 

. 

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• 

.. 

kd 

• 

' 

• 

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ff/A/G 

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WL 

MM 

'A/GTf 

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r  ML  / 

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60%       65%         70%         2S%         &%          85%        30%       Sit, 

C.2 


FIG.  411a.— Showing  thejAbsence  of  any  Law  of  Relationship  between  Shearing  Strength 
and  Tensile  Strength  of  Steel  Plates  when  the  Shearing  Strength  is  determined  by 
Punching  Tests.  (Experiments  made  at  Washington  University  by  Messrs  Condron, 
Harrington,  and  Norton.  See  a  full  account  of  these  in  Engr.  News,  vol.  xxxn 
(1894),  p.  164.) 

limit,  it  does  not  appreciably  increase  the  elongation,  neither  does  it  bring 
the  "normal"  and  "dull  red"  specimens  much  nearer  together  in  the 
matter  of  the  elastic  limit.  It  might  fairly  have  been  assumed  that  annealing 


500 


THE  MATERIALS  OF  CONSTRUCTION. 


would  have  removed  the  effects  of  rolling  at  a  low  heat,  as  it  always  does  the 
effects  of  cold  working,  but  it  has  not  done  so  in  this  instance., 

358a.  Punching  Tests  of  Steel  Plates.  —  It  has  been  claimed  *  that 
structural  steel  may  be  tested  by  punching  in  place  of  the  ordinary  tension 
tests.  This  subject  was  very  fully  investigated  at  the  Washington  University 
Testing  Laboratory,  as  the  subject  for  a  thesis,  by  Messrs.  Harrington  and 
Norton,  in  1894,  assisted  by  Mr.  T.  L.  Condron,  C.E.,  and  it  was  concluded 
that  no  definite  relationship  could  be  established  between  the  results  of 
punching  and  of  tension  tests  on  steel  plates  of  varying  quality  and  thick- 
The tests  were  made  with  autographic  stress-diagrams  of  every  test, 


ness. 


and  hundreds  of  tests  made  on  steel  plates  of  known  chemical  composition 
and  tensile  properties.  Fig.  41  la  is  here  given  as  one  of  many  such  studies 
made  of  the  results,  all  going  to  show  that  the  punching  tests  could  not  be 
employed  as  tests  of  acceptance  under  any  set  of  specifications.! 

359.  Effects  of  Quenching  and  of  Annealing  on  Structural  Steel.  —  It 
is  not  generally  known  that  quenching  from  a  bright  cherry-red  heat  has  a 


64000 


43000 


20000 


,20 


-$K 

k 


FIG.  412.  FIG.  413. 

FIG.  412.— Average  Effects  of  Quenching  Soft  Steel  (0.10  C.)  from  a  Dull  Red  Heat. 
Each  point  the  mean  of  six  tests.  (Campbell's  Structural  Steel,  p.  52.) 

FIG.  413.— Effects  of  Quenching  a  Very  Low  Carbon  (0.057  C.)  Steel  at  Different  Tem- 
peratures. (Campbell's  Structural  Steel,  p.  53.) 

marked  effect  on  the  softest  grades  of  open-hearth  steel.     That  it  has  is 
shown  by  Figs.  412  and  413,  where  a  steel  having  a  normal  tensile  strength 

*  By  Alfred  E.  Hunt   before   the  World's   Engineering  Congress,  Chicago,  1893. 
Trans.  Am.  Soc.  Civ.  Engrs.,  vol.  xxx.  p.  181. 

t  See  an  illustrated  article  by  Mr.  Condron  in  Engr.  News,  vol.  xxxii.  p.  164. 


THE  STRENGTH  OF  STEEL. 


501 


of  48,500  Ibs.  per  square  inch  (Fig.  412)  is  raised  to  63,500  Ibs.  per  square 
inch  by  quenching.  The  apparent  elastic  limit  is  raised  from  32,000  to 
40,000  Ibs.  per  square  inch;  the  elongation  is  lowered  from  32  to  20  per 
cent  in  8  in. ;  and  the  reduction  of  area  is  raised  55  to  63  per  cent.*  This 
reveals  also  the  difference  between  the  elongation  and  the  reduction  of  area 
as  characteristics  of  steel.  The  highest  grade  of  steel  wire,  having  a 
strength  of  200,000  Ibs.  per  square  inch  and  upward,  and  having  an  elonga- 
tion of  but  one  or  two  per  cent,  will  commonly  show  a  reduction  of  area  of 
over  60  per  cent.  That  is,  the  stretch  largely  occurs  at  the  necked-down 
portion  only.  The  cold-bending  test  is  a  test  of  the  reduction  of  area  rather 
than  of  the  elongation.  In  Fig.  413  the  effects  are  shown  of  quenching  soft 
open-hearth  steel  from  various  temperatures  from  a  dull  red  to  a  bright  red 
heat.  These  two  figures  both  show  that  the  softest  steel  is  greatly  changed 
by  quenching,  but  since  the  reduction  of  area,  has  been  raised  its  capacity 
for  making  short  bends  has  been  increased. 

When  the  cold-bending  test  is  specified,  after  quenching,  therefore,  it 
would  appear  from  Fig.  412  that  this  soft  material  is  better  able  to  stand 

SO 


3^?%/% 


«s 


m\ 


^    L, 


S 


50 


/  xt/  ^  /K  X7 

FIG.  414.— Effect  of  Annealing  2  in.  X  f  in.  Open-hearth  Steel  Bars  of  Different  De- 
grees of  Hardness.     (Campbell's  Structural  Steel,  p.  210.) 

this  test  than  it  was  in  its  normal  condition.  This  matter  should  be  proved 
by  direct  bending  tests,  however,  before  being  accepted  as  true.  If  this 
proves  to  be  true,  then  quenching  greatly  improves  the  steel  for  all  purposes. 
The  annealing  process  seems  always  to  reduce  the  ultimate  strength  and 
the  elastic  limit  for  all  grades  of  steel,  the  lowering  of  the  latter,  as  shown 


The  chemical  composition  was  C  =  0.105;  Mu  =  0.343,  P  =  0.009;  S  =  0.024. 


502  THE  MATERIALS  OF  CONSTRUCTION. 

in  Fig.  414,  being  about  25  per  cent.  The  elongation  is  very  slightly 
increased  and  the  reduction  of  area  somewhat  decreased.  By  the  annealing 
process,  therefore,  about  one  fourth  of  the  effective  strength  of  a  steel  mem- 
ber is  sacrificed,  while  its  cold-bending  capacity  is  probably  reduced.  It 
would  seem,  therefore,  that  it  should  be  practised  only  when  necessary  to 
remove  severe  internal  stresses  produced  by  cold  working. 

360.  The  Billet  Test  is  Characteristic  of  the  Final  Rolled  Bars  and 

Plates }£r.  GUS  C.  Ilenning  has  shown  *   that  specimen  billets  rolled  or 

forged  from  the  sample  of  the  steel  dipped  from  an  open-hearth  furnace  to 
test  its  quality  give  results  which  are  truly  characteristic  of  the  products 
rolled  from  that  heat.     The  tests  of  these  sample  billets  are  commonly  called 
"  heat  tests,"  since  one  such  is  made  for  each  heat.     If  the  results' of  these 
tests  agree  closely  with  the  tests  on  specimens  cut  from  the  structural  forms, 
bars,  and  plates  which  are  rolled  from  this  material,  then  these  latter  may 
be  omitted  and  reliance  placed  wholly  upon  the  heat  tests.     The  results  of 
221  such  corresponding  sets  of  tests  are  given  in  Table  \XV. 

This  table  also  contains  results  of  tests  of  specimens  cut  from  annealed 
bars  and  plates.  In  all  the  specimen  tests  on  rolled  and  annealed  bars  and 
plates  an  extensometer  was  used,  reading  to  0.0001  in.  by  micrometer-screw 
with  electric  contact,  as  shown  in  Fig.  271.  The  true  elastic  limits  were  there- 
fore carefully  and  accurately  determined.  This  was  not  done  with  the  heat 
or  billet  tests,  so  that  no  comparison  can  be  made  on  this  score.  The  yield- 
points  were  observed  by  the  "  drop  of  the  beam,"  which  is  a  quite  accurate 
method  with  this  quality  of  material  if  the  test  is  not  made  too  rapidly. 

361.  The  Distribution  of  the  Elongation  over  an  8-inch  specimen  1£  inches 
in  diameter  is  shown  in  Fig.  415.     This  shows  that  the  stretch  is  nearly 
uniform  until  the  maximum  load  is  reached,  after  which  it  begins  to  neck 
down.     From  this  on  to  final  rupture  the  stretch  is  almost  wholly  confined 
to  the  necked-down  portion.     Thus  while  the  elongation  near  the  ends  was 
only  21  per  cent  and  the  average  elongation  was  about  28  per  cent,  the 
elongation  at  the  plane  of  rupture  was  75  per  cent. 

The  Reduction  of  Area  of  rectangular  specimens  is  difficult  to  obtain 
accurately,  on  account  of  the  resulting  curved  outlines  arising  from  the 
greater  contraction  in  the  middle  portions.  This  action  is  well  shown 
in  Fig.  410.  If  the  reduced  section  is  calipered  at  about  one  fourth  the 
width  from  each  side,  the  area  resulting  from  taking  the  product  of  these  two 
dimensions  will  be  insignificant. 

362.  The  Compressive  Strength  is  the  Elastic  Limit. — Table  XXVI  con- 
tains the  results  of  some  of  the  most  careful  experiments  ever  made  on  the 
compressive  strength  of  steel  bars  (see  also  Fig.  294).     These  were  made  by 
Mr.  Chas.  A.  Marshall,  C.E.f    These  results  show  a  practical  identity  in  the 
apparent  elastic  limit,  or  yield-point,  in  tension  and  compression,  and  also 

*  In  Trans.  Am.  Soc.  Mech.  Engrg.,  vol.  xin. 
f  See  foot  note  p.  341. 


THE  STRENGTH  OF  STEEL. 


503 


TABLE    XXV. — COMPARISON    OF    KESULTS    OF    TESTS    OF    SPECIMEN"    BILLETS 
AND    OF    SPECIMENS    CUT    FROM    FINAL   ROLLED    FORMS. 

TESTS  OF  BARS. 


Size  of 
Bar. 

Kind  of 
Test. 

Billet 
Rolled 
Annealed 

Elastic 
Limit. 

35.867 
37,850 

Yield-point 

Tenacity. 

Per  cent 
Elonga- 
tion in  8" 

Per  cent 
Reduc- 
tion in  8" 

Modulus  of 
Elasticity. 

30,191,000 
29,799,000 
31,290,000 

No.  of 

Tests 
Averaged 

7"  x  7/8"  A 

47,267 
39,006 
39,083 

73.440 
71,540 
69,990 

23.6 
25.1 
25.3 

39.5 
51.6 
54.2 

3 
3 
3 

7"xH"  -j 

Billet 
Rolled 
Annealed 

33,622 
35,060 

45,666 
39.334 
40,140 

70,845 
71,102 
67,930 

23.3 
23.2 
26.3 

41.7 
44.7 
57.0 

29,498,000 
30,837,000 
31,567,000 

4 
5 
2 

7"xlA"-j 

Billet 
Rolled 
Annealed 

29,650 
33,110 

44,498 
36.620 
40,035 

70,392 

69,750 
70,860 

23.3 
24.1 
25.2 

41.3 
48.9 
53.7 

30,793,000 
29,939,000 
31,410,000 

3 
2 

2 

7"xli"  j 

Billet 
Rolled 
Anaealed 

34,725 

38,125 

45,010 
38.255 
40,725 

71  ,035 
72,108 
69,800 

22.6 

22.8 
24.6 

37.1 
40.2 
42  .4 

29,150,000 
29,889.000 
31,444,000 

2 
4 
2 

7"xlA"j 

Billet 
Rolled 
Annealed 

31,550 

35,688 

46,103 
36,635 
39,860 

69.820 
67,795 
68,154 

24.0 
26.0 
25.8 

41.8 
55.0 
54.8 

29,900.000 
30,921,000 
31,451,000 

3 
2 
4 

7"xl|"   | 

Billet 
Rolled 
Annealed 

32,890 
35,470 

45,508 
37,480 
39,579 

70,320 

71,561 
70,450 

24.2 

21.6 
23.4 

42.5 
38.5 
44.7 

30,127,000 
30,166.000 
30,934,000 

14 
19 
11 

r'xi^'j 

Billet 
Rolled 
Annealed 

29.606 
34,162 

46,319 

34,882 
37,834 

71,395 
67.560 
68.070 

23.1 
24.2 
24.6 

38.3 
46.0 
48.0 

29,850,000 
30,430,000 
30,510,000 

10 
12 
11 

,„,.{ 

Billet 
Rolled 
Annealed 

33,730 
34,620 

47,350 
38,000 
38,500 

71,595 
70.090 
69,840 

22.0 
26.2 
27.5 

37.9 

48.8 
57.5 

29,840.000 
30,528,000 
30,528,000 

1 
1 

7"xlH"j 

Billet 
Rolled 
Annealed 

32,082 
37,170 

45,698 
36,315 
39,152 

70,665 
71,269 
69,688 

23  7 
23.3 
25.4 

41.5 
43.5 
50.1 

29,500.000 
30,759,000 
31,268,000 

7 
11 
10 

7"xij"  | 

Billet 
Rolled 
Annealed 

38,100 
35,000 

44,950 
41,040 
37,550 

63,770 
74,060 
65,420 

25.0 
19.8 
22.9 

40.0 
42.0 
35.0 

28,285,000 
31,647,000 
30,746,000 

1 
1 

1 

7"xlfi"j 

Billet 
Rolled 
Annealed 

29,080 
32,100 

45,740 
31.510 
36,640 

72,330 
66,180 
73,670 

23.6 
26.2 
23.7 

38.1 
54.9 
50.4 

29,455,000 
32,479,000 
31,302,000 

1 

1 
1 

-H 

Billet 
Rolled 
Annealed 

29,000 
33,650 

46,320 
32,750 
39,060 

71,630 

71,370 
71,280 

20.8 
25.0 
24.5 

34.9 
52.9 
53.7 

28,535,000 
28,420,000 
31.078000 

1 

1 
1 

Average   -j 

Billet 
Rolled 
Annealed 

33.327 
35,1(57 

45,869 
36,819 
39,013 

71.020 
70,365 
69,596 

23.3 
23.9 
24.9 

39.5 
47.5 
46.0 

29,594,000 
30,484,000 
31,127,000 

Total  No. 
161 

TESTS  OF  PLATES. 


I 

Billet 

47,700 

80.966 

20.5 

35  8 

30.601,000 

5 

1/2" 

Rolled 

47,048 

48,120 

86,572 

19.7 

36.3 

30.061.000 

5 

1 

Annealed 

39,523 

43,698 

75,155 

24.7 

47.3 

29,901,000 

9 

I 

Billet 

47,737 

82,113 

20.6 

33.9 

29,690,000 

6 

5/8"      1 

Rolled 

45.895 

48,008 

81,753 

19.9 

40.7 

30,763,000 

6 

\ 

Annealed 

39,792 

42,066 

74,624 

22.1 

47.2 

30,591,000 

9 

( 

Billet 

51  ,936 

81,818 

21.1 

38.8 

29,612,000 

5 

3/4"      ] 

Rolled 

44,692 

47,643 

79,127 

21.8 

42.3 

30,879.000 

5 

I 

Annealed 

38,267 

40,067 

72,961 

22.9 

47.8 

31,167,000 

7 

I 

Billet 

50,130 

84,970 

19.7 

30.8 

29,220,000 

1 

13/16"    ^ 

Rolled 

45.580 

48,280 

88,230 

19.0 

31.2 

29,188,000 

1 

1 

Annealed 

41,730 

43,590 

77,010 

25.8 

50.8 

30,528,000 

1 

Average  -j 

Billet 
Rolled 
Annealed 

40,S04 
39,828 

49,376 
48,013 
42,355 

S2.467 
83,920 
74,938 

20.5 
20  1 
23  9 

34.8 
37.6 
48.3 

29,782,000 
30.223.000 
30,722,000 

Total  No. 
60 

004 


THK  MATKRIALS  OF  CONSTRUCTION. 


that  the  ultimate  strength  of  short  burs  is  tho  apparent  elastic  limit.  They 
also  show  the  lessened  elastic  limit  ami  elongation  for  the  larger  sixes,  all 
being  rolled  from  the  same  billet,  the  ultimate  strength  not  varying  much. 
Thus  for  a  reduction  of  ultimate  strength  from  3  "»•  to  XU  in.  diameter  of 


:••• 


U&OL 

/  J  o  4  S  0  7  8  9  M  // 
Fio.  415.— Showing  tho  Distribution  of  tho  tilonpition  on  (00,000-UO  Stool  Specimen 
Sin.  loiii*  niul  U  in.  in  ilitunotor.     (Fr.  Com.  /&';>.,  vol.  ui.  PI.  111.) 

A.-l  per  cent,  we  have  a  reduction  in  the  elastic  limit  of  ^0  per  cent,  and  in 
the  percentage  of  elongation  of  HO  per  cent,  the  ratio  of  length  to  diameter 
remaining  constant. 

363.  The  Elastic  Limit  in  Compression  marks  the  beginning  of  lateral 
llowing  of  the  metal,  and  the  stress  under  which  this  action  begins  depends 


T1IK  STltKNUTll  OF  8TKKL. 


505 


TAHLK  XXVI. — MILD  STKKL  IN  TKNSION  AND  COMIMtKSSKW. 
Comparison  of  Tensile  ami  Compressive  Results  with  Results  of  Tests  on  Short  Columns 
of  Round  ami  Square  Huts  from  J  in.  to  '.".  in.  in  diameter,  all  rolled  from  one  blow 
of  Hessemer  Steel.  Elongations  ineaau red  on  a  length  equal  to  ten  diameters,  by 
means  of  the  Marshall  Kxtensometer  shown  in  Fi#.  271.  (From  Marshall's  Kx- 
pcriments,  Trans.  Am,  Soc.  C.  K.,  vol.  xvn,  Tables  I  and  II.) 


1  l.i'.!  u-  Limit  in  rounds 
|»T  Sijii;iri«  IlU'll 

l  liim.n,-  si  i,-n:-.ili  in 
Pounds  per  s.|ii.ni-  liu'li 

KloiiKUtion. 

KV.III.-II..II 

Spocimon 

in  Compi*. 

in  Cnmpr. 

of  A  roil. 
I'eraentage. 

iii  Tension. 

for^.i. 

in  Tension. 

,„,;,.,,, 

l.cll^lll  of 

Hpeclnien. 

of 

Klongullon, 

8/4 

45,181 

45,000 

08,711 

44,1)70 

8 

20.4 

45.8 

48,880 

45,855 

08,240 

48,540 

10 

25  .  0 

81).  8 

Ij. 

40,1)08 

42,880 

07,500 

40,455 

12 

20.4 

48.0 

11 

89,795 

42,015 

00,51)8 

40,150 

15 

25.4 

81).  8 

u 

89.105 

41,225 

66,866 

81),  700 

18 

21.8 

88.8 

2 

•  88,207 

89,170 

05,008 

40,800 

20 

28  .  1) 

27.8 

^i 

87.055 

80,542 

05,400 

88,080 

22 

18.7 

17.2 

2i 

80,100 

80,840 

85,050 

25 

10.2 

Means 

40,103 

41,129 

66,935 

40,350 

21.9 

35.0 

Fro.  410. — Showini;  the  Manner  in  which  Rectangular  Steel  Test-spceimens  reduce  fn 
Cross-section.     (Kinjr.  ,AVyr.s,  vol.  xxxm.  p.  272.) 

on  tho  freedom  with  whicli  the  nietn,!  can  How  l.-itonilly.  Thus  in  Kifj.  417 
we  luive  it  column  compressed  over  its  full  cross-section  with  freedom  to  flow 
laterally  in  every  direction.  'This  is  the  usual  condition  under  which  tho 
elastic  limit  in  compression  is  found. 

In  Kiij.  1  IS  the  specimen  is  compressed  uniformly  over  a  portion  onlv  of 
its  surface,  and  when  the  elastic  limit  is  exceeded  the  metal  finds  escape  hy 
flowing  laterally  against  the  resistance  of  a,  ring  of  unstressed  metal.  This 
is  a  condition  of  restricted  ilow,  and  evidently  the  elastic  limit  now  is  much 
higher  than  before. 


506 


THE  MATERIALS  OF  CONSTRUCTION. 


In  Fig.  419  only  the  metal  towards  the  centre  of  the  compressed  surface 
is  constrained  to  flow  under  the  direct  stress,  but  in  attempting  to  move 
laterally  it  is  held  by  a  ring  of  metal  which  is  confined  and  compressed  ver- 
tically, though  inside  its  elastic  limit.  To  find  an  escape  the  metal  at  the 


I  I 


V, 


I  I 


FIG.  417. 
Free  Flow. 


FIG.  418. 
Restricted  Flow. 


FIG.  419. 
Confined  Flow. 


centre  must  force  its  way  against  a  much  wider  ring  of  metal  than  in  the 
second  case,  and  hence  the  elastic  limit  now  is.  very  much  higher  than  when 
pressed  by  a  flat  disk. 

The  elastic  limit  in  compression,  therefore,  is  a  meaningless  expression 
unless  the  conditions  of  lateral  flow  are  also  stated. 

364.  The  Author's  Tests  of  Areas  of  Contact  between  Car-wheels  and 
Rails. — In  Figs.  420  and  421  are  shown  a  series  of  actual  areas  of  contact 
obtained  by  pressing  sections  of  a  cast-iron  car-wheel  and  of  a  locomotive 
steel  driving-wheel  upon  the  cylindrical  top  surface  of  a  steel  rail.  This 
was  done  in  a  testing-machine  in  such  a  way  that  there  was  no  rocking 
motion  and  the  area  of  contact  was  clearly  distinguished.* 

The  areas  of  these  surfaces  of  contact  were  determined  by  a  planimeter, 
and  these  are  plotted  to  their  corresponding  loads  in  Fig.  422.  It  will  be 
seen  that  these  plot  in  nearly  a  straight  line  through  the  origin.  If  such  a 
law  be  assumed,  it  follows — 

1.  That  the  area  of  contact  increases  directly  with  the  load. 

2.  That  the  mean  intensity  of  pressure  is  a  constant  for  all  loads, 

3.  That  in  these  experiments  this  mean  intensity  of  compressive  stress, 
for  all  loads,  was  about  82,000  Ibs.  per  square  inch. 

4.  Since  the   maximum  deformation  (at  the  centres  of  these  areas)  is 
twice  the  average  deformation  (assuming  the  volumetric  deformation  to  be 
that  of  a  segment  of  a  paraboloid  of  revolution),  then  the  maximum  com- 
pressive-stress  intensity  for  all  loads  is  about  164,000  Ibs.  per  square  inch. 

5.  Since  no   measurable  permanent  set  was  produced  by  any  of  these 
loads  on  either  wheels  or  rail,  it  follows  that  the  "apparent  clastic  limits  "  of 
the  materials  had  not  been  reached  for  this  condition  of  contact,  although 
the  ordinary  elastic  limit  of  the  rail  material,  for  a  free  flow  as  in  Fig.  417, 
was  about  50,000  Ibs.  per  square  inch. 


*  See  a  full  account  of  these  tests,  showing  other  areas  of  contact,  in  Trans.  Am.  8oc. 
Civ.  Engrs.,  vol.  xxxn.  p.  270.  1894. 


THE  STRENGTH  OF  STEEL. 


FIG.  420.— Steel  Driver,  44  in 
diam.     Flat  tread 


FIG.  421.— Chilled  Wheel, 
33  in.  diam.     New. 


508 


THE  MATERIALS  OF  CONSTRUCTION. 


BQOOO 


WflOO 


/  V 

;/ 


OF  .CIA/TACT  tlf  SGj.  //V 


'0-4  &G 

FIG.  422. — Showing  the  Relation  between  the  Total  Load  and  the  Area  of  Contact  be- 
tween "Wheels  and  Rails.     (Johnson,  in  Trans.  Am.  Soc.  C.  E.,  vol.  xxxii.) 


/4000 


/0,000 


4M0& 

r\ 


2,000 


'A  ML 


'V 


/A 


/6 


0     2     4      6      8      JO     tf 
FIG.  423.—  The  Elastic-limit  Loads  per  Lineal  Inch  of  Rollers  of  Various  Diameters. 
(Crandall  and  Marston,  in  Trans.  Am.  Soc.  Civ.  Engrs.,  vol.  xxxii.  p.  120  (1894).) 


THE  STRENGTH  OF  STEEL. 


509 


These  are  important  conclusions,  and  should  be  supplemented  and 
supported  by  further  observations  of  this  character. 

In  Fig.  423  are  shown  the  results  of  tests  made  by  Profs.  Crandall  and 
Marston  to  find  the  elastic-limit  loads  on  steel  cylinders  resting  on  or 
between  steel  plates.  These  results  show  that  the  elastic  loads  vary  directly 
with  the  diameters,  these  loads  per  lineal  inch  of  rollers,  for  mild  structural 

steel,  being 

p  =  8SOd, (1) 

where  p  =  elastic-limit  load  in  pounds  per  lineal  inch,  and  d  —  diameter  of 
roller  in  inches. 

365.  The  Moduli  of  Elasticity  in  Tension  and  Compression  for  various 
sizes  and  qualities  of  steel  and  wrought  iron  are  given  in  Table  XXVII, 

TABLE   XXVII. — COMPARISON   OF    MODULI   OF   ELASTICITY   IN   TENSION   AND 

COMPRESSION.* 
All  results  given  in  one-thousaud-pound  units,  identical  material. 


STEEL— Tensile  Strength  less  than  100,000 
Ibs.  per  Square  Inch. 


SPRING-STEEL. — Tensile  Strength  144,000 
Pounds  per  Square  Inch. 


Size 
of 
Bar. 

Tension. 

Compression. 

Size 
of 
Bar. 

Tension. 

Compression. 

E1, 
First 
Loading. 

E* 

Second 
Loading. 

El 
First 
Loading. 

E.t 

Second 
Loading. 

EI 

First 
Loading. 

E* 

Second 
Loading. 

El 

First 
Loading. 

EI 

Second 
Loading. 

1  rd. 

&  sq. 

Ird. 

|rd. 

Asq. 

1  rd. 
Ird. 
Ird. 
Ird. 

mean 

30,190 
29,850 
29,280 
29,830 
29,420 
29,550 
29,240 
29,400 
30,000 

34,420 
29,850 
29,500 
29,150 
29,640 
29,630 
29.960 
30,420 
30,370 

29,450 

28,070 
28,780 
28,580 
28,380 
28,680 
30,070 
28,980 
29,260 

29,740 
29,010 
29,420 
29,420 
28,670 
28,830 
30,490 
29,790 
29,810 

Ird. 
Ird. 

T8iysq. 

T8i>  sq- 

29,480 
29,390 

28,880 
29,200 

29,760 
29,580 
29,420 
29,200 

28,880 
28,880 
29,090 
29,090 

29,300 
29,200 
29,220 
29,350 

mean 

29,237 

29,490 

28,985 

29,267 

29,529 

30,371 

28,884 

29,464 

WROUGHT  IRON. 


Size 
of 
Bar. 

|rd. 
Ird. 
Ird. 
1  rd. 
f  sq. 
|  sq. 
Isq. 

Tension. 

Compression. 

Size 
of 
Bar. 

Tension. 

Compression. 

El 

First 
Loading. 

Et 
Second 
Loading. 

El 

First 
Loading. 

EI 
Second 
Loading. 

E\ 

First 
Loading. 

EV 

Second 
Loading. 

First 
Loading. 

#2 

Second 
Loading. 

26,800 
26,980 

27',  540 
28,990 
27,790 
27,800 

27.500 
27,410 
26,700 
27,540 

29.180 
27,900 

25.840 
25,920 
25,670 
26,020 
27,420 
25,650 
26,490 

26,160 
26,240 
26,440 
26,350 

27,790 
27,300 

IS 

1  rd. 
Ird. 

frd. 

28,290 
27,590 
28,290 
26,580 
30,190 

28,290 
28,570 
28,480 
28,480 
30,190 

27,100 
27,250 
27,430 
26,500 
29,520 

26,734 

27,990 
28,570 
28,570 
28,180 
29,910 

mean 

27,894 

28,203 

27.590 

*  From  experiments  by  Charles  A.  Marshall,  M.  Am.  Soc.  C.  E.,  reported  in  Trans. 
Am.  Soc.  Civ.  Engrs.,vo\.  xvn.  pp.  62-3. 


510 


TEE  MATERIALS  OF  CONSTRUCTION. 


these  results  also  being  from  Marshall's  experiments.  They  show  the  rela- 
tion between  the  modulus  of  elasticity  as  obtained  from  the  first  and  from 
the  second  loading,  the  first  loading  not  having  been  carried  beyond  the 
elastic  limit.  As  the  modulus  from  the  second  loading  is  always  a  little 
larger  than  that  obtained  from  the  first  loading,  it  shows  that  on  the  first 
loading  there  is  always  a  small  permanent  set,  and  that  moduli  of  elasticity 
should  be  observed  only  after  a  load  has  been  imposed  and  removed.  The 


4Q000 


8QM0 


O  .0005         .OO / 

0  .0005          .00/  i00/5 

FIG.  424. — Showing  Variations,  in  the  Modulus  of  Elasticity  of  Steel  Eye-bars,  66,000 
Ibs.  T.  S.,  after  the  Elastic  Limit  has  been  Passed.     ( Wat.  ATS.  Rep.  1883.) 

failure  to  do  this  may  explain  some  of  the  low  values  of  this  modulus  which 
are  often  given. 

If  the  specimen  be  stretched  much  beyond  its  elastic  limit,  however,  the 
elastic  limit  is  lowered  after  each  such  higher  loading,  as  indicated  in 
Fig.  424. 

366.  Modulus  of  Elasticity  Independent  of  the  Other  Mechanical  Prop- 
erties.— In  Table  XXVIII  are  given  the  average  values  of  the  moduli  of 
elasticity  from  262  determinations  on  steels  of  five  degrees  of  hardness. 
The  mean  values  for  these  five  classes  do  not  in  any  case  differ  from  the 
mean  of  all  by  more  than  six  tenths  of  one  per  cent.  As  the  mean  of  all  is 


THE  STRENGTH  OF  STEEL. 


511 


TABLE  XXVIII. — MODULI  OF  ELASTICITY  OF  STEEL  ON  FIRST  LOADINGS, 
WITH  VARYING  PERCENTAGES  OF  CARBON,  ONE  SPECIMEN  FROM 
EACH  HEAT.* 


Number 
of  Heats 
and  Tests. 

Average 
Percentage 
of  Carbon. 

Moduli  of  Elasticity  E,  in  Pounds  per  Square  Inch. 

Kind  of  Steel. 

Lowest  Value. 

Highest  Value. 

Average  Value. 

33 
8 
107 
89 
25 

9 

11 
24 
34 

72 

28,750,000 
29,210,000 
28,310,000 
28,140,000 
28,680,000 

31,540,000 
30,670,000 
31,180,000 
30,910,000 
30,860,000 

29,924,000 
30,020,000 
29,996,000 
29,672,000 
29,919,000 

29,866,000 

Bessemer 
Open  -hearth 

Bessemer 
Open-hearth 

Weighted  mean  value  = 

*  From  Marshall's  Experiments,  2'rans.  Am.  Soc.  C.  E.,  vol.  xvn.  p.  64. 

TABLE    XXIX. — TENSILE    TESTS    ON    ROUND    STEEL    RODS    FROM    1    TO    3 
INCHES   IN   DIAMETER,   ANNEALED   AND    UNANNEALED. 

Each  recorded  result  is  the  mean  of  three  tests.     All  the  results  in  one  horizontal  line 
are  for  tests  on  material  cut  from  the  same  three  bars.f 


Size. 

Elastic  Limit  $  in  Pounds  per 
Square  Inch. 

Ultimate  Strength  in  Pounds 
per  Square  Inch. 

Ratio  of  Elastic  Limit  to 
Ultimate  Strength. 

Unannealed. 

Annealed. 

Unannealed. 

Annealed. 

Unannealed. 

Annealed. 

Diam. 
in  in. 

1 

? 
? 

Rods 
100  in. 
long. 

Rods 
10  in. 
long. 

Rods 
10  in. 
long. 

Rods 
100  in. 
long. 

Rods 
10  in. 
long. 

Rods 
10  in. 
long. 

Rods 
100  in. 
long. 

Rods 
10  in. 
long. 

Rods 
10  in. 
long. 

72.7 
67.5 
62.0 
60.3 
58.3 

43,330 
42,400 
36,520 
34,130 
35,700 

46,970 
43,300 
39,570 
37,230 
36,530 

45,130 
42,170 
36,270 
34,300 
33,500 

63,810 
62,507 
61,320 
58,950 
58,550 

66,050 
65,020 
61,420 
60,300 
59,830 

62,010 
62,460 
58,490 
56,790 
57,370 

67.8 
67.8 
59.5 
57.8 
60.9* 

71.1 
66.5 
64.4 
61.7 
61.0 

Size. 


Diameter 
in  inches. 


1 

i* 

f 


Percentage  of  Elongation. 

Percentage  of  Reduction. 

Modulus  of 

Elasticity  of  the 

Unannealed. 

Annealed. 

Unannealed. 

Annealed. 

100-inch  Bars  Un- 

annealed in 

Pounds  per 

Rods  100  in. 

Rods  10  in. 

Rods  10  in. 

Rods  100  in. 

Rods  10  in. 

Rods  10  in. 

Square  Inch, 

long 

long. 

long. 

long. 

long. 

long. 

First  Loading. 

19.21 

25.6 

22.1 

60.2 

61.1 

65.7 

27,300,000 

21.42 

26.9 

24.9 

55.3 

55.0 

58.4 

21,100,000 

25.62 

30.9 

30.4 

58.8 

59.4 

62.5 

30,000,000 

23.50 

31.4 

32.5 

56.9 

54.9 

62.7 

30,600,000 

17.34 

30.6 

33.9 

54.6 

49.8 

61.2 

28,400,000 

From  Kirkaldy's  Report,  1891,  reports  M  and  HH. 

This  is  the  true  elastic  limit  on  the  first  loading  ;  it  was  about  5  per  cent  below  the 
yield-point,  or  the  "apparent  elastic  limit." 


512 


THE  MATERIALS  OF  CONSTRUCTION 


THE  STRENGTH  OF  STEEL. 


513 


29,866,000,  and  this  from  first  loadings,  it  will  not  be  appreciably  in  error 
to  call  the  modulus  of  elasticity  of  steel  30,000,000.  (See  also  Figs.  398  to 
403,  where  tensile  stress  indicated  for  an  elongation  of  0.001  is  uniformly 
about  30,000  Ibs.  per  square  inch,  thus  giving  a  modulus  of  elasticity  of 
30,000,000.) 

367.  The  Effect  of  Annealing  on  Steel  Before  and  After  Overstraining.— 
In  Table  XXIX  are  given  results  of  annealing  steel  bars  which  have  never 
been  stressed  or  worked  cold.     In  Table  XXX  are  given  the  results  of  tests 


FIG.  426. — Effect  of  Length  of  the  Reduced  Section  on  the  Strength  and  Ductility  of 
Steel.  James E.  Howard  (in  charge  of  Tests  at  the  Watertown  Arsenal)  before  Inter. 
Eag.  Cong.  1893.  Section  of  Nau,  Eng.  and  Marine  Arch.,  vol.  n,  J.  Wiley  &  Sous, 
New  York. 

on  overstrained  steel  which  was  afterwards  annealed.  It  will  be  observed 
that,  while  it  has  little  effect  on  soft  steel  in  the  normal  state,  the  anneal- 
ing largely  restores  the  original  qualities  to  overstrained  soft  steel,  though 
it  does  not  fully  do  so.  The  high  moduli  of  elasticity  in  compression  given 
in  Table  XXX  for  both  the  annealed  and  the  unannealed  specimens  should 
be  accepted  with  caution  as  being  probably  erroneous. 


514 


THE  MATERIALS  OF  CONSTRUCTION, 


368    The  Effect  of  Varying  the  Length  of  the  Reduced  Section.*— "  The 

following  results  of  the  tests  of  six  specimens  from  the  same  1^-in.  steel 
bar  illustrate  the  apparent  elevation  of  elastic  limit  and  the  changes  in  other 
properties  due  to  changes  in  the  lengths  of  stems  which  were  turned  down 
in  each  specimen  to  0.798  in.  diameter.  (See  also  Fig.  426.) 


Description  of  Stem. 

Elastic  Limit, 
Pounds  per 
Square  Inch. 

Teasile  Strength, 
Pounds  pei- 
Square  Inch. 

Contraction  of 
Area, 
Per  Cent. 

1  00  '  long                

64  900 

94,400 

49.0 

*50       "         

65,320 

97,800 

43.4 

25       ••                  .         ....          

68,000 

102  420 

39.6 

Semicircular  srroove   0  4"  radius 

75  000 

116  380 

31  6 

Semicircular  srroove    1/8''  radius  

86  000  about 

134,960 

23  0 

90,000,  about 

117,000 

Indeterminate 

' 

"  These  tests  show  the  progressive  elevation  of  the  elastic  limit  as  the 
stems  of  the  specimens  were  shortened,  and  the  corresponding  effect  upon 
the  tensile  strength.  The  contraction  of  area,  of  course,  diminishes  as  the 
other  two  features  increase  in  value. 

"  The  lower  tensile  strength  of  the  specimen  having  the  V-shaped  groove 
was  probably  due  to  the  excessive  concentration  of  stress  at  the  bottom  of 
the  groove  from  inability  to  elongate  or  contract,  fracturing  the  metal  more 
in  detail  than  happened  to  the  other  specimens/' 

In  Fig.  427  are  shown  the  results  of  similar  tests  made  by  M.  Duguet  on 
hard  steel  and  by  M.  Barba  on  soft  steel  bars.  In  both  of  these  sets  of  ex- 
periments the  very  short  reduced  sections  have  a  greatly  increased  breaking 
strength. 

In  this  connection  it  must  be  remembered  that  in  ductile  metals,  where 
the  reduced  'section  has  appreciable  length,  there  is  a  great  reduction  of 
area,  so  that  the  stress  per  square  inch  at  rupture  on  the  actual  section  at 
that  time  is  about  twice  the  tensile  strength  as  computed  on  the  original 
cross-section.  In  the  very  short  or  grooved  reduced  sections,  however,  the 
material  has  no  opportunity  to  reduce  in  area,  and  hence  the  actual  ruptur- 
ing stress  is  developed  over  the  full  original  area.  In  the  case  ot  the  sharp 
V-shaped  groove  the  material  is  likely  to  tear  apart  by  failing  first  at  the 
outer  edges-  In  other  words,  the  stress  is  not  uniformly  distributed  over 
the  cross  section. 

In  Fig  428  are  plotted  the  results  of  tests  of  the  same  grade  of  steel 
(54,000  Ibs  tensile  strength),  when  tested  in  the  standard  form,  with  par- 
allel sides,  and  when  grooved  as  has  long  been  required  for  the  U.  S.  Marine 
Service  The  effect  of  the  groove  is  to  raise  the  tensile  strength  from  7000 


*  Quoted  paragraphs  and  table  taken  from  a  paper  by  James  E.  Howard  read  before 
the  World's  Engineering  Congress,  1893. 


THE  STRENGTH  OF  STEEL. 


515 


Ibs.  per  square  inch  on  the  f  inch  plate  to  over  12,000  Ibs.  per  square  inch 
on  the  1-inch  plate.     The  grooved  specimen,  furthermore,  gives  little  or  no 


4000 


80000 


7000 


S0.000 


/T0S-ff0t/M0  SfCf/OA/S* 


. 


33 


fff 


FIG.  427. — Showing  the  Effect  of  the  Form  of  the  Reduced  Section  on  the  Tensile 
Strength  of  Two  Kinds  of  Steel.     (Fr.  Com.  Rep,,  vol.  in,  p,  40.) 

indication  of  the  elastic  limit,  and  no  indication  of  the  percentage  of  elonga- 
tion. The  requirement  of  grooved  specimens  on  this  service  will  probably 
soon  be  abandoned. 

369.  Nickel-steel,*  being  an  alloy  of  mild  steel  with  about  3|-  %  of  nickel, 
has  a  very  high  elastic  limit  and  ultimate  strength,  combined  with  great 
ductility,  as  shown  in  Fig.  429.  This  alloy  is  doubtless  destined  to  play  a 

*  First  made  by  Marbeau  in  1885,  and  used  for  armor-plate  in  1890.  The  price  of 
nickel  steel  was  40  to  45  cents  a  pound  in  1894.  For  a  complete  study  of  the  influence 
of  nickel  on  pure  iron,  in  all  proportions,  see  Berlin  Testing  Laboratory  Communica- 
tions, 1896,  vol.  iv.  p.  222. 


516 


THE  MATERIALS  OF  CONSTRUCTION. 


€5000 


5500 


\ 


es 


60 


55 


50 


FIG.   428. — Showing  Relative  Results  from  Grooved  and  Parallel-sided   Specimens 
(Campbell's  Structural  Steel,  p.  223.) 


4004         &00S 
FIG,  429.— Tension  Tests  on  Nickel-steel     (Wat.  Ars.  Rep.  1894,  pp.  199  «ml  VQO  ) 


THE  STRENGTH  OF  STEEL. 


517 


leading  part  wherever  great  elastic  strength  and  a  reasonable  ductility  are  re- 
quired. It  would  seem  to  be  especially  fitted  for  bicycle  tubing  and  spokes, 
aerial  experimentation,  the  reciprocating  parts  of  locomotive  engines,  motor 
carriages,  etc.,  as  well  as  for  armor-plates. 

370.  The  Mechanical  Properties  of  Steel  as  Affected  by  Forging  and 
Rolling. — In  Fig.  430  is  shown  the  cross-section  of  a  steel  shaft  16  inches  in 
diameter  (which  broke  soon  after  being  put  in  service)  from  which  eight  test- 


£0006 


0./S 


0:30      0.35 
0.20      0.2S 


FIG.  430.— Showing  the  Varying  Character  in  the  Material  in  Different  Parts  of  the 
Cross-section  of  a  Large  Steel  Shaft  when  forged  under  a  Ten-ton  Hammer.  ( Wat. 
Ars.  Rep.,  1885.) 


specimens  were  cut,  lying  symmetrically  in  a  diametral  section  as  shown. 
Four  of  these  were  tested  as  cut  from  the  shaft.  The  other  four  were  forged 
down  after  cutting  out.  The  plotted  results  show* — 

1.  The  elongation  of  the  unforged  specimens  varied  from  21  per  cent  in  the 


518 


THE  MATERIALS  OF  CONSTRUCTION. 


specimen  taken  from  near  the  surface  of  the  shaft  to  %  per  cent  in  the  specimen 
U--  —  80-  ____  4  coming  from  near  the  centre.  In  the  forged  specimens, 
however,  taken  from  the  opposite  side  of  the  disk,  the 
elongation  varied  from  28  per  cent  near  the  surface  of 
the  shaft  to  24  per  cent  near  the  centre,  thus  showing 
that  the  material  was  identical  throughout  when  it  had 
been  similarly  worked.  In  other  words,  the  material 
near  the  centre  of  the  shaft  was  in  its  primitive  con- 
dition when  first  cast,  while  that  near  the  surface  was 
that  of  well-rolled  steel.  This  shows  the  necessity  of 
forging  large  shafts  under  enormously  heavy  hammers, 
or,  better,  the  necessity  of  using  only  hollow-forged 
shafts  for  such  service. 

Steel  car-axles  are  now  rolled  and  then  finished  by 
drawing  through  a  die.  In  Fig.  431  are  shown  the 
effects  of  a  series  of  16  blows  upon  a  steel  car-axle,  3f 
in.  in  diameter,  turned  over  after  each  second  blow,  of 
a  drop  weighing  1640  pounds  and  falling  from  18.8  to 
28  ft.  The  deflections  from  each  blow  varied  from  8-J- 
to  13  in.,  but  the  -axle  remained  unbroken  after  this 
severe  treatment. 

371.  Steel-  welded  Tubes.—  In  Tables  VII  and  VIII, 
pp.  130  and  131,  it  was  shown  that  steel  may  be  welded 
as  securely  as  wrought  iron,  but  that  the  temperature 
at  which  this  material  welds  perfectly  lies  within  com- 
paratively  narrow  limits.  If  heated  above  the  upper 
limit  the  steel  melts  and  oxidizes,  and  it  is  then  said  to 
have  been  burned.  If  not  heated  up  to  the  lower  limit 
=r-  "7=3  an  imPei'fect  weld  is  formed.  To  effect  a  good  weld 

FALL  OF  28  FT       in   a   common   blacksmith's   forge   therefore   requires 
FIG.  431.  —Showing  the  great  ^^\\  an(j  care>     Qn  the  other  hand,  where  steel 

plates  USed  f°r  tube'making  ai'e  ™iformly  heated   in 


amtee 

Car-axle  when  tested  a  furnace    i]1  which   the   temperature   can   be   main- 

by   Impact  without  tained  constant  and  of  a  given  degree,  these  may  then 

Rupture.      Wt.     of  be  welded  perfectly,  especially  if  this  be  done  by  ma- 

drop  ==  1640      Ibs.  chinery.     The  evidence  of  such  perfect  welds  is  fur- 

nished in  Figs.  432  and  433,  where  welded  steel  tubes 

are  shown  to  have  been  subjected  to  the  most  severe  abuse,  by  cold  crushing 

and  twisting,  and  without  any  failure  appearing  in  any  of  the  welded  joints. 

372.  Wrought-iron  and  Steel  I  Beams  and  Plate  Girders.—  When  rolled 

into  I  beams,  or  when  plates  and  angles  are  riveted  together  to  form  a  plate 

.girder,  the  true  elastic  limit  of  the  beams  and  girders  is  below  that  of  the 

specimen  test-pieces  cut  from  the  webs  and  flanges.     The  ultimate  strength 

of  the  wrought-iron  beams  and  girders  is  higher  than  that  of  the  specimens, 


THE  STRENGTH  OF  STEEL. 


B  ^ 

<-*      O 


520 


THE  MATERIALS   OF  CONSTRUCTION. 


FIG.  4:53.—  P]ximples  of  Welded  Steel  Tubes  twisted  Cold,  made  by  the  National  Tube 
Works.     (From  The  Iron  Age,  Sept.  17,  1896.) 


€0000 


S0000 


0        0.2S       0JO      0.75       /.00 

FIG.  434.— Bending  Tests  on  Steel  and  Wrought-iron  I  Beams,  7.6  in.  high,  on  60-iu. 
span.     (Tetmajer,  vol.  in,  PL  IV.) 


FIG.  435.— Showing  Variation  in  Moduli  of  Strength  and  Stiffness  of  Steel  I  Beams  with 
Varying  Depth.     (Tetmajer's  Communications,  vol.  in,  PI.  V.) 


THE  STRENGTH  OF  STEEL. 


521 


but  with  the  steel  beams  and  girders  the  reverse  is  the  case.  All  these 
relations  are  shown  by  the  following  tables,  which  are  the  results  of  a  series 
of  very  careful  tests  made  by  Professor  Tetmajer.  The  moduli  of  elas- 
ticity of  the  rolled  or  riveted  forms  are  not  appreciably  lower  than  those  of 
the  materials  of  which  they  are  composed;  but  this  modulus  and  also  the 
moduli  of  strength  seem  to  decrease  with  increasing  heights  of  beam,  as 
shown  in  Fig.  435. 

TABLE   XXXI. ELASTIC  LIMIT  AND  ULTIMATE  STRENGTH  OF  WROUGHT-IRON 

I    BEAMS   AS    COMPARED    WITH     RESULTS    OF   TESTS   OF    SPECIMENS    CUT 
FROM   THE   WEBS   AND   FLANGES   OF   THE    SAME. 

(Each  result  is  the  mean  of  two  tests.     From  Prof,  von  Tetmajer's  Communications, 

vol.  iv.) 


Depth 
of 

Elastic  Limit  in  Pounds  per 
Square  Inch. 

Ultimate  Strength  in  Pounds  per 
Square  Inch. 

Per  Cent  of 
Elongation. 

Modulus  of 
Elasticity  of 

Beam 

I  Beams  in 

in 
Inches. 

Web 

Speci- 
men. 

Flange 
Speci- 
men. 

Beam, 
Extreme 
Fibre. 

Web 

Speci- 
men. 

Flange 
Specimen. 

Beam, 
Extreme 
Fibre. 

Web 

Speci- 
men. 

Flange 
Speci- 
men. 

Pounds  per 
Square  Inch. 

4 

40,520 

42,230 

35,120 

54,740 

57,300 

62,850 

10.4 

19.1 

28,600,000 

6 

38,680 

36,400 

33,270 

51,330 

53,750 

56,450 

7.8 

25.5 

28,300,000 

8 

35,690 

34,840 

33,840 

50.900 

51,900 

53,890 

11.7 

18.5 

28,300,000 

10 

36,120 

34,410 

31,000 

48,490 

51,330 

51,620 

13.1 

158 

27,500,000 

12 

31,000 

32,280 

31,570 

44,930 

52,610 

53,180 

9.1 

19.7 

26,500,000 

14 

33,840 

33,700 

27,370 

51,470 

53,460 

53,890 

17.9 

20.5 

27,700,000 

16 

33,130 

31,140 

29,720 

50,480 

50,190 

52,470 

11.9 

22.9 

27,600,000 

Means 

35,572 

35,000 

31,770 

50,334 

52,934 

53,478 

11.7 

20.2 

27,800,000 

TABLE     XXXII. ELASTIC     AND      ULTIMATE      STRENGTH      OP    WROUGHT-IRON 

PLATE  GIRDERS  COMPOSED  OF  A  SOLID  WEB,  FOUR  ANGLES,  AND  TWO 
COVER-PLATES,  AS  COMPARED  WITH  THE  TENSILE  STRENGTH  OF  THE 
PARTS  COMPOSING  THEM. 

(Each  result  is  the  mean  of  tests  on  two  beams  or  on  four  tension  specimens.     From 
von  Tetmajer's  Communications,  vol.  iv.)  * 


Test-specimen. 

Elastic 
Limit  in 
Pounds  per 
Square 
Inch. 

Ultimate 
Strength 
in  Pounds 
per  Square 
Inch. 

Percentage 
of  Elonga- 
tion in 
8  Inches. 

Percentage 
of 
Reduction 
of  Area. 

Modulus  of 
Elasticity  of 
Girders  in 
Pounds  per 
Square  Inch. 

Web-plate  lengthwise  
crosswise       . 

40,950 

36,120 
35,120 
34,690 

53,320 
37,400 
51,040 
48,350 

14.1 
0.5 
13.9 

8.4 

16.2 
0.4 
17.0 
14.6 

Cover-plates  lengthwise  
Angles  lengthwise  

Plate  girders  16  in.  high  

25,590 
29,860 

52,330 
52,040 
50,620 
47,210 

.... 

i 

25,990.000 
25,250,000 
26,430.000 
26,220,000 

20  in.  high  
"          "       24  in    high          .    . 

"          "        28  in.  hifh  

27,580 

Mean  of  the  parts 

38,720 
27,680 

47,050 
50,550 

9,2 

11.8 

Mean  of  the  girders 

25,970,000 

522 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE  XXXIII. — ELASTIC  AND  ULTIMATE  STRENGTH  OF  MILD-STEEL  PLATE 
GIRDERS  COMPOSED  OF  A  SOLID  WEB,  FOUR  ANGLES,  AND  TWO  COVER- 
PLATES,  AS  COMPARED  WITH  THE  TENSILE  STRENGTH  OF  THE  PARTS 
COMPOSING  THEM. 

(Each  result  is  the  mean  of  tests  on  two  beams  or  on  four  tension  specimens.     From 
von  Tetmajer's  Communications,  vol.  iv.) 


Test-specimen. 

Elastic 
Limit  in 
Pounds  per 
Square 
Inch. 

Ultimate 
Strength 
in  Pounds 
per  Square 
Inch. 

Percentage 
of 
Elongation 
in  8  Inches. 

Percentage 
of 
Reduction 
of  Area. 

Modulus  of 
Elasticity  of 
Girders  in 
Pounds  per 
Square  Inch. 

52,330 
53,040 
51,190 
39,960 

32,560 
35,690 
33,700 
32,280 

64,560 
65,980 
64,840 
53,750 

24.1 
20.0 
25.0 
31.0 

59.5 
46.2 
562 
66.1 

"          crosswise  

Plate  girders  16  iu   hi0*!!         .... 

55,310 
54,320 
55,030 
53,750 



27,700,000 
28,310,000 
28,510,000 
28,140,000 

"           «       20  in    high  

"          "       24  in   high 

"          «<       28  in   hi°'h  

Mean  of  the  parts  

49,130 
33,550 

62,280 
54,600 

25.0 

57.0 

^Vlean  of  the  girders 

28,165,000 

373.   The  Effect  on  Mild  Steel  of  Stressing  it  Beyond  its  Elastic  Limit. 

— Both  wrought  iron  and  rolled  steel,  in  their  normal  state,  have  "  apparent 
elastic  limits"  in  tension  and  in  compression  numerically  about  equal.  If 
this  material  be  stressed  much  beyond  these  limits,  however,  in  either  direc- 
tion, its  elastic  limit  in  this  direction  is  numerically  raised  to  about  the  limit 
of  its  greatest  stress,  while  the  elastic  limit  in  the  opposite  direction  is 
greatly  lowered  or  even  reduced  to  zero.  This  is  well  shown  in  Figs.  436 
and  437.  Thus  in  Fig.  436  a  steel  specimen  was  stressed  several  times  in 
tension  between  zero  and  45,000  Ibs.  per  square  inch,  when  it  was  put  in 
compression  to  50,000  Ibs.  per  square  inch,  at  which  load  it  passed  its  elastic 
limit  and  began  to  flow.  After  compressing  it  0.007  of  its  length  the  load 
was  removed  and  simultaneous  readings  of  load  and  deformation  taken 
while  the  load  was  coming  off,  as  shown  in  the  figure.  The  specimen  was 
then  worked  between  10,000  Ibs.  tensile  and  a  like  compressive  stress,  then 
between  zero  and  20,000  Ibs.  tension,  and  zero  and  40,000  Ibs.  tension,  and 
finally  between  zero  and  50,000  Ibs.  per  square  inch  tension,  when  it  had 
lengthened  0.004  beyond  its  original  length  as  shown  in  Fig.  436.  It  was 
then  put  in  compression  under  a  load  of  50,000  Ibs.  per  square  inch,  which 
compressed  it  0.004  below  its  original  length,  while  a  subsequent  tensile 
stress  of  50,000  Ibs.  brought  it  nearly  back  to  its  previous  deformed  length 
under  this  tensile  stress.  The  diagram  shows  the  following  remarkable  facts: 
1.  A  permanent  deformation  of  one  half  of  one  per  cent  in  either  tension 
or  compression  entirely  destroys  the  perfect  elasticity  of  the  material  under 
the  opposite  kind  of  stress. 


THE  STRENGTH  OF  STEEL. 


523 


This  is  shown  by  the  fact  that  the  stress-diagram  becomes  a  curved  line 
under  all  stresses  of  one  kind  after  having  been  given  a  small  permanent  set 
in  the  opposite  direction.  Hence  we  have : 

2.   The  elastic  field  which  is  symmetrically  placed  about  the  line  of  zero 


stress  in  the  normal  specimen  becomes  wholly  limited  to  that  side  of  this  axis 
on  which  the  stress  has  exceeded  the  elastic  limit. 

A  similar  set  of  experiments,  plotted  in  Fig.  437,  was  followed  by  the 
annealing  of  the  bar,  after  which  it  showed  again  its  normal  elastic  limits  in 


524 


TEE  MATERIALS  OF  CONSTRUCTION. 


both  tension  and  compression,  which  were  in  turn  again  destroyed  by 
deforming  the  annealed  bar  0.003  beyond  its  elastic  limits,  as  before. 
Hence  we  may  say : 

3.  Annealing  an  overstressed  liar  restores  it  fully  to  its  normal  condition 
of  perfect  elasticity  in  both  tension  and  compression. 

Both  of  these  diagrams  are  very  instructive  and  will  bear  close  study. 
Many  more  such  could  be  plotted  from  the  tabulated  results  found  in  the 


BEfQ/?£  ANNEAL/ A/G 
JFTEf?  AMNEALM& 


FIG.  437.— Alternate  Tensile  and  Compressive  Distortions  of  a  Steel  Bar  before  and  after 
Annealing.     (Wat.  Ars.  Rep.  1889.) 

Reports  of  the  Watertown  Arsenal,  from  which  the  data  for  these  were 
obtained. 

The  effect  on  the  ultimate  strength  of  60,000-lb.  steel  of  pulling  it 
nearly  to  final  rupture  is  shown  in  Fig.  43 7 a.  This  also  gives  some  idea  of 
the  homogeneity  of  the  steel.  Here,  after  the  specimen  had  necked  down 
under  the  tensile  load,  but  before  it  broke,  it  was  removed,  a  continuous 
screw-thread  cut  on  it,  and  a  series  of  grooves  were  cut  in  it  as  shown.  The 
bar  was  then  broken  in  tension  at  all  these  grooves  in  succession,  with  the 
results  as  shown  in  Fig.  43 la.  The  original  tensile  strength  was  about 
57,000  Ibs.  per  square  inch,  the  final  breaking  stress  on  the  grooved  sections 
was  about  100,000  Ibs.  per  square  inch,  while  the  final  stress  on  the  groove 
placed  at  the  centre  of  the  necked-down  portion  was  155,000  Ibs.  per  square 
inch.  A  portion  of  this  increase  in  strength  is  due  to  the  normal  difference 
between  the  strength  of  a  grooved  and  of  a  parallel-sided  specimen,  as 
shown  in  Fig.  427.  After  allowing  for  this  difference  there  still  remains  a 
great  increase  of  strength  due  to  the  previous  drawing  out  and  the  interven- 
ing rest  the  specimen  had  experienced. 


THE  STRENGTH  OF  STEEL. 


525 


The  results  of  similar  tests  on  unstressed  or  normal  bars  are  shown  in  the 
original  plate  from  which  Fig.  437#  was  taken,  which  go  to  show  that  grooved 
sections  on  the  same  steel  bar  may  develop  breaking  tensile  stresses  which 
differ  from  each  other  by  as  much  as  20  to  25  per  cent.  No  such  differences 


ffffoaf  Tfsr/A/0 


I 

t 

<^r  •  • 

•"*5  

69 


FIG.  437«. 

would  be  observed  on  specimens  with  parallel  sides  cut  from  the  same  bar, 
and  hence  we  must  conclude  that  results  of  tests  on  grooved  sections  of  steel 
are  very  erratic  and  unreliable. 

374.  Shearing  Resistance  of  Steel. — Prof.  A.  B.  W.  Kennedy,  by  means 
of  the  apparatus  shown  in  Fig.  311,  obtained  values  of  tensile  and  shearing 
resistances  of  various  steels  given  in  Table  XXXIV. 

TABLE    XXXIV. — SHEARING    RESISTANCE    OF    STEEL.* 


Tensio 

a  Test. 

Shearing 

Ratio  of 

Kind  of  Steel. 

Number 
of  Tests 
Averaged. 

Elastic  Limit, 
Pounds  pei- 
Square  Inch. 

Ult.  Strength, 
Pounds  per 
Square  Inch. 

Strength, 
Pounds  per 
Square  Inch. 

Shearing  to 
Tensile 
Strength. 

Landore  Siemens  steel.. 

Weardale  Bessemer  " 
Bessemer  steel  .    . 

2 

2 
3 
6 
6 

4 

37,500 
40,000 
37,000 
40,600 
44,000 
51  500 

57,000 

63,500 
64,000 
69,000 
71,000 
78  000 

47,500 
51,000 
52,000 
56.000 
51,000 
64  000 

0829 

0800 
0.811 
0.807 
0.715 
0  823 

Crucible        "  ..!!..!.. 

4 
2 

62,000 
69  500 

82,000 
116  000 

59,000 
74  000 

0.721 
0  632 

Bessemer      ''     ... 

2 

70  000 

118  000 

79  000 

0  670 

*  From  Proc.  Inst.  Meek,  Engrs.  1885,  p.  262. 

From  the  above  table,  which  is  simply  corroborative  of  a  vast  amount  of 
similar  data,  we  may  reasonably  use  0.8  as  the  ratio  of  shearing  to  tensile 
strength  of  mild  or  structural  steel. 


526 


THE  MATERIALS  OF  CONSTRUCTION. 


375.  The  Frictional  Resistance  of  Riveted  Joints.* — The  contraction  of 
rivets  in  cooling  is  always  much  more  than  their  elastic  stretch.  Thus  if  the 
modulus  of  elasticity  be  taken  at  30,000,000,  and  the  elastic  limit  of  rivet- 
steel  at  30,000  Ibs.  per  square  inch,  then  the  elastic  stretch  is  0.001  of  the 
length.  But  as  the  contraction  per  degree  F.  is  O.OOOOOG5,  it  follows  that 

(  -\  =  154°  F.  change  of  temperature  would  bring  rivets  to  their 

VO.OOOOOG5J 

elastic  limit  if  they  were  not  allowed  to  contract.     Evidently,  therefore,  all 

well-driven  rivets  in  plates  which  are  tightly  clamped  together  when  the  rivet 


o 


'0L02     0.04 

FIG.  438.  ^  FIG.  439. 

FIG.  438.— Showing  the  Successive  Stages  of  the  Slipping  of  Riveted  Plates. 

(M.  Dupuy  in  An,  d.  Ponts  et  Chaussees,  1895.) 

FIG.  439. — Autographic  Stress-diagram  of  a  Double-strap  Butt-riveted  Joint  with  oue 
rivet  on  each  side  of  joint,  showing  slips  at  aa'  and  bb'.  (An.  d.  Ponts  el  Chaussees, 
vol.  ix,  1895.) 

is  driven,  and  so  held  till  the  rivet  cools,  are  left  in  a  state  of  tension  exceed- 
ing their  elastic  limits.  If  the  coefficient  of  starting  friction  be  taken  at 
0.4,  and  the  elastic  limit  of  steel  rivets  be  taken  at  30,000  Ibs.  per  square 
inch,  and  of  iron  rivets  at  25,000  Ibs.  per  square  inch,  it  follows  that  the 
frictional  resistance  would  be  12,000  Ibs.  per  square  inch  of  rivet  section  for 

*  Riveted  joints  are  a  kind  of  structure  the  strength  and  design  of  which  do  not  fall 
within  the  scope  of  this  work.  The  elements  of  the  strength  of  such  structures,  however, 
are  properly  treated  here. 


THE  STRENGTH  OF  STEEL,  527 

steel  rivets,  and  10,000  Ibs.  per  square  inch  of  rivet  section  for  iron  rivets, 
in  lap-joints,  and  twice  these  amounts  for  butt-joints  with  two  cover-plates, 
since  in  that  case  there  are  two  frictional  surfaces  on  each  of  which  the  full 
tensile  stress  in  the  rivets  acts.  Theoretically,  therefore,  we  might  expect  a 
frictional  resistance  of  12,000  or  24,000  Ibs.  per  square  inch  of  rivet-surface 
for  lap  and  butt  joints  respectively  when  the  rivets  are  of  steel,  and  of 
10,000  or  20,000  Ibs.  when  the  rivets  are  of  iron. 

Since  the  plates  are  clamped  together  much  more  firmly  when  steam  or 
hydraulic  riveting-machines  are  used  than  when  the  rivets  are  driven  by 
hand,  so  the  experiments  show  a  much  higher  frictional  resistance  for 
machine-driven  rivets.  To  secure  the  greatest  frictional  efficiency  the 
machine  pressure  should  remain  on  until  the  rivet  has  cooled,  but  in  ordinary 
commercial  work  this  is  seldom  done. 

M.  Dupuy  has  carefully  and  fully  investigated  this  question.*  He  shows 
that  after  cooling  the  rivet  does  not  fully  fill  the  hole,  as  shown  in  Fig. 
438  (1).  The  first  slip,  therefore,  when  a  butt-joint  has  one  rivet  on  each 
side  as  shown  in  Fig.  438  (2),  is  that  which  brings  the  centre  plate  against 
the  rivet.  This  is  shown  at  a  and  a'  in  Fig.  439,  this  being  a  reduced  auto- 
graphic stress-diagram  for  the  joint  shown  in  Fig.  438.  The  slip  at  a 
occurred  under  a  load  of  17,500  Ibs.  per  square  inch  of  rivet  area  when  the 
centre  plate  came  up  against  the  rivet  on  one  side  of  the  joint,  and  the  slip 
at  a'  marks  a  similar  movement  on  the  other  side  at  18,500  Ibs.  per  square  inch 
of  rivet  area.  After  these  movements  had  occurred  the  load  was  increased  to 
28,000  Ibs.  per  square  inch  of  rivet  area,  when  the  rivet-heads  slipped  on  the 
cover-plates,  as  shown  in  Fig.  438  (3),  and  on  the  stress-diagram  in  Fig.  439 
at  b.  Soon  after  the  same  action  occurred  at  the  other  rivet,  marking  the 
deformation  at  V  in  Fig.  439.  All  these  four  slips  were  sudden,  and  were 
accompanied  by  a  sharp  report  like  a  pistol-shot.  After  the  spaces  had  all 
closed  up  in  this  way  the  deformation  was  gradual,  and  the  rivet  would 
then  be  acting  as  a  bolt,  aud  be  subjected  to  a  shearing  stress  and  deforma- 
tion as  shown  in  Fig.  438  (4). 

376.  The  Stresses  per  Square  Inch  of  Rivet  Section  at  which  the  First 
Slipping  Occurs,  as  determined  by  M.  Dupuy,  with  an  extensometer 
(called  by  him  an  elasticimeter),  are  given  in  Fig.  440.  They  are  presented 
in  this  form  in  order  that  the  relative  frictional  efficiencies  of  different 
methods  of  riveting  may  be  read  at  a  glance.  These  results  were  obtained 
by  cutting  the  plate  along  the  centre  line  of  the  rivets  and  then  pulling  out 
the  two  halves  of  these  rivets  as  indicated  in  the  figure.  In  this  way  the 
frictional  resistance  of  the  rivet-heads  was  correctly  obtained  without  any 
complication  with  bearing  or  shearing  resistance,  as  must  always  be  the  case 
when  pulling  actual  riveted  joints. 

From  tests  on  riveted  joints  made  at  the  Watertown  Arsenal  (1882)  we 
find  the  following  values  of  frictional  resistance  on  plates  with  elongated 
holes,  hand-riveting: 

*  ILI  An.  d.  Fonts  et  Cliaussees,  7th  series,  vol.  ix,  1895 


528 


THE  MATERIALS  OF  CONSTRUCTION. 


Frictional  Resistance 
on  one  Surface  in 
Pounds  per  Square 
Inch  of  Rivet  Area. 

Steel  plates,  f-in.  iron  rivets,  If -in.  grip,  lap-joint,  4  tests 14,550 

Iron       "       |-in.     "        "       1-in.       '•«        "       "      4     "    14,100 

f-in,     "        "       1-in.      "     butt- joint,  2 cover-plates,  2  tests          9,000 

It  thus  appears  that  the  frictional  resistance  is  not  twice  as  much  on  a 
butt-joint  having  two  cover-plates  as  it  is  on  a  lap-joint.     The  reason  may 

/£000\ 


P/?L~SS.  C#A/T'0.  X/VET  Wtf/TE  //Pf 


PEL/EVED 


CONT'D. 


RED 


tf/VET/NG 


WH/TE 


ff/l/ET  COLO 


FIG.  440. — The  Slipping  Resistance  of  Steel  Rivets  in  Pounds  per  Square  Inch  of  Rivet 
Cross-section  for  Various  Conditions  of  Driving.  Each  result  is  the  overage  of  25 
tests  on  single  rivets  from  £  inch  to  1.2  inches  diameter.  Plates  and  rivets  cut  on 
the  diametral  lines  and  each  half  of  rivet  pulled  out  as  shown.  (M.  Dupuy  in  An. 
d.  Fonts  et  Chaussees,  1895,  p.  105.) 


Jt 


.02"  .04"  "36"  .Of 

FIG.  441.— Stress-diagram  of  Test  of  Double-butt-strap  Riveted  Joint.  Steel  plates  0.662 
in.  thick  and  20  in.  wide.  Thirteen  f-in.  steel  rivets,  machine-driven,  on  each  side 
of  joint.  Drilled  holes  §f  in.  diameter.  (Wat.  ATS.  Rep.  1887,  p.  892.) 

be  that  the  distortion  of  the  lap-joint  increases  the  frictional  resistance  by 
putting  an  additional  tensile  stress  on  the  rivet  from  the  bending  of  the 
plates. 


THE  STRENGTH  OF  STEEL. 


529 


Since  the  frictional  resistance  is  thus  seen  to  depend  directly  upon  the 
total  shearing  area  of  the  rivets,  whether  these  be  in  single  or  in  double 
shear  (although  in  double  shear  the  frictional  resistance  on  each  bearing 
surface  seems  to  be  less  than  in  single  shear),  there  would  seem  to  be  no 
advantage  in  designing  riveted  joints  for  frictional  resistance.  It  seems 


/QOOO 


.08  M  .06"  .08" 

FIG.  442. — Stress-diagram  of  a  Test  of  a  Double-butt-strap  Riveted  Joint.  Steel  plates 
£  in.  thick  and  16.5  in.  wide.  Eleven  1-in.  steel  rivets,  machine-driven,  in  three 
rows  on  each  side  of  joint.  Straps  |  in.  thick.  Drilled  holes  ly1^  in.  diameter. 
(Wat.  Ars.  Rep.  1887,  p.  901.) 

probable,  however,  that  all  riveted  joints  in  practice  do  their  work  through 
friction  alone,  and  that  in  no  case  are  the  rivets  subjected  to  either  shearing 
or  bearing  stress.  But  when  the  joint  is  dimensioned  for  shear,  it  is  likely 
to  be  also  properly  designed  for  frictional  resistance.  In  the  case  of  double 
shear,  riveted  joints  are  usually  proportioned  for  bearing  stress,  and  here  it 


FIG.  443. — Showing  Manner  of  Failure  of  a  Triple-riveted  Steel  Plate.     Figures  indicate 
thickness  of  plate  at  that  place.     (Wat.  Ars.  Rep.  1887.) 

would  seem  to  be  proper  to  make  due  allowance  for  the  frictionai  resistance 
which,  for  all  working  loads,  will  at  least  greatly  reduce  the  bearing  stress. 

The  frictional  resistance  of  joints  containing  double  or  triple  rows  of 
rivets  cannot  be  observed,  because  all  the  rivets  do  not  draw  with  the  same 
tensile  force,  and  hence  the  slipping  is  progressive  and  without  any  sudden 
manifestation.  This  is  well  shown  by  Figs.  441  and  442,  which  are  charac- 
teristic of  a  great  many  such  tests  made  at  the  Watertown  Arsenal.  Evi- 


530 


THE  MATERIALS  OF  CONSTRUCTION. 


dently  it  would  be  impossible  here  to  locate  the  point  of  initial  slipping. 
This  explains  Prof.  Kennedy's  discrepant  results  on  this  class  of  joints,  as 
recorded  in  the  Proceedings  of  the  Institution  of  Mechanical  Engineers 
(London)  for  the  years  1885  and  1888.  He  here  records  the  loads  for 
which  "  visible  slip  began";  but  as  he  used  only  a  hand  magnifying-glass, 
and  the  movement  was  a  gradually  progressive  one,  it  would  be  quite 
impossible  to  obtain  consistent  or  rational  results.  In  fact,  for  such  joints 
no  such  stage  of  the  test  exists,  since  the  slipping  does  not  occur  over  the 
entire  joint  at  any  one  time. 

377.  The  Bearing  Resistance  of  Steel  and  Iron  Plates  is  shown  in  Fig. 
444.     This  is  seen  to  increase  directly  with  the  distance  of  the  hole  from 


4000A  £/$> 


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M 


.pW/cf      /A 


f 


1   /ffYlfJ  O. 


S.00 


2:00 


FIG.  444.— Bearing  Resistance  on  Rivet-holes  at  Rupture  by  Tearing  Out  of  Hole.     The 
steel  plates  were  of  60,000  Ibs.  tensile  strength.     ( Wat.  Ars.  Rep.  1882.) 


the  edge  of  the  plate.     When  this  distance  agrees  with  ordinary  practice 
the  resistance  is  so  high  that  it  would  seem  a  working  bearing  stress  of 


THE  STRENGTH  OF  STEEL. 


531 


16,000  Ibs.  per  square  inch  might  be  employed  for  iron,  and  of  24,000  Ibs. 
per  square  inch  for  steel,  plates.  The  stresses  here  plotted  were  the  bearing 
stresses  at  rupture,  where  the  plates  had  so  reduced  in  thickness  as  to 


<o 


, 


3$MA    tWTH 


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WA/Wtfff 


ftf  AT  Bt 


•/fltiM 


FIG.  445. — Variation  in  Strength  of  |-iu.  Plate  for  Varying  Widths  at  Bottom  of  Groove. 
Each  plotted  result  is  the  mean  of  from  three  to  eight  tests.     ( Wat.  Ars.  Rep.  1882.) 


FIG.  446. — Effects  of  Punching,  Reaming,  and  Shearing.  No.  5  has  punched  holes  and 
sheared  edges.  No.  6  lias  punched  and  reamed  holes  and  planed  edges.  (Engr. 
News,  vol.  XXXITI.  p  291.) 


532 


THE  MATERIALS  OF  CONSTRUCTION. 


destroy  all  frictional  resistance.  Much  more,  then,  could  high  working 
stresses  be  employed,  since  for  these  the  frictional  resistance  is  very  great. 
The  author  believes  that  the  ordinary  rules  for  proportioning  riveted  joints 
might  well  be  modified  so  as  to  allow  higher  bearing  stresses,  especially  on 
steel.  With  wrought  iron,  especially  when  the  stress  is  transverse  to  the 


FIG.  447.— Effects  of  Shearing  and   Punching  on  Bessemer-steel  Plate  |  in.  thick. 
Specimen  7  had  sheared  edges  and  punched  holes.     Specimen  8  had  planed  edges 
\       and  drilled  holes.     (Engr.  News,  vol.  xxxm.  p.  291.) 


I,  2,  3. 

FIG.  448.— Showing  that  Injury  iu  Case  of  Shearing  and  Punching  comes  from  the 
Compression  of  the  Metal  Necessary  to  Produce  the  Shear.  Nos.  1  and  2  were  bent 
cold,  with  the  compression  edge  on  convex  side  ;  No.  3  was  bent  with  compression 
edge  on  concave  side.  (Engr.  News,  vol.  xxxm.  p.  290.) 

fibre,  more  care  must  be  exercised,  as  this  material  is  liable  to  be  very  weak 
in  this  direction. 

'*?  378.  The  Tensile  Strength  of  Grooved  Plates  is  a  measure  of  the  tensile 
strength  of  a  riveted  joint  when  failure  occurs  by  tearing  the  plate.  This 
strength  is  found  to  be  a  function  of  the  width  of  the  net  section  at  the 


THE  STRENGTH  OF  STEEL. 


533 


bottom  of  the  groove,  as  well  as  of  the  method  of  obtaining  the  hole,  and  of 
the  character  of  the  material.  These  effects  are  all  shown  in  Fig.  445  for 
£-in.  plates  of  wrought  iron  and  of  56,000-lb.  steel.  The  steel,  being  more 
ductile,  is  stronger  in  the  grooved  than  in  the  plain  (standard)  section, 
while  the  reverse  is  the  case  with  wrought  iron,  except  with  drilled  speci- 
mens, where  the  width  of  the  net  section  was  less  than  If  in. 

379.  The  Injurious  Effect  of  Punching  and  Shearing  is  Found  on  the 
Compressed  Side  Only. — In  punching  and  shearing  cold  metal  it  seems  to 
be  the  compression  produced  by  the  shears  or  by  the  die-plate  which  injures 
the  metal  here  and  makes  it  brittle  by  cold  flowing.     This  is  clearly  shown 
in  Figs.  446  and  448.     Thus  in  Fig.  446  (5),  when  the  punched  plate  is 
bent  with  the  punch  (or  upper)  side  in  tension,  no  cracks  appear  about  the 
punched  holes,  but  when  the  die   (or  lower)   side  of  the  hole  is  on  the 
tension  side  of  the  bent  plate,  Fig.  446  (5),  many  cracks  appear  and  radiate 
from  such  openings.     When  these  holes  are  reamed,  however,  as  in  Fig.  446 
(6),  no  such  cracks  develop. 

Similarly,  in  Fig.  448,  when  a  bar  is  cut  off  with  two  sheared  edges,  and 
if  both  pressed  corners  (from  having  turned  the  plate  over)  are  on  the  same 
side  of  the  bar,  and  this  side  be  put  in  tension,  as  in  Fig.  448  (1),  then  it 
breaks  as  shown.  If  these  pressed  edges  are  on  opposite  sides  of  the  bar,  it 
breaks  only  at  that  edge,  as  in  (2),  while  if  both  sheared  edges  have  been 
planed,  as  in  (3),  it  bends  without  cracking. 

380.  The  Avoidance  of  Scarfed  Joints. — This  may  be  effected  as  shown 
in  Fig.  449.     Here  lap-joints  are  used  in  one  direction  and  butt-joints  in 


I 


B 

i 

talking  Joint.         \ 

[666666666 


66666 


Calking  Joinf- 


q°oT 


Calkinq  Joirrr^ 


C)  DOOOpOOOOO 


OOiOO 

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Section  A- B. 

FIG.  449.— Proper  Method  of  Joining  Riveted  Work  in  Stand-pipes  and  Boilers  when 
single  butt-straps  are  used.     (Engr.  News,  vol.  xxxm.  p.  290.) 

the  other,  with  one  cover-plate.  This  requires  twice  as  many  rivets  in  this 
direction,  but  it  makes  a  much  neater  and  stronger  construction  and  it  avoids 
the  heating  of  one  corner  of  every  plate  for  the  purpose  of  scarfing  it  down 
to  a  thin  edge,  as  must  be  done  where  three  plates  come  together  in  a 


534  THE  MATERIALS  OF  CONSTRUCTION. 

lap-joint.     In   the   figure   all   the   outer   edges   are   planed  to  a  bevel  for 
calking.* 

381.  Steel  Specifications. — For  three  sets  of  specifications,  by  a  Com- 
mittee of  the  American  Society  of  Civil  Engineers,  by  the  Association  of 
American  Steel  Manufacturers,  and  by  Mr.  H.  H.   Campbell,   Supt.   Steel 
Works  at  Steelton,  Pa.,  see  Appendix  D. 

382.  The  Influence  of  the  Form  of  the   Thread  on  the  Strength  of 
Screw-bolts. — This  subject  has  been  investigated  by  Prof.  Martens,f  and  his 
results  are  here  given. 

Two  grades  of  mild  steel  were  used  for  these  bolts,  all  of  which  were  cut 
from  round  bars  originally  35  mm.  (1.4  in.)*  in  diameter.  The  softer 
material,  having  a  tensile  strength  of  53,500  Ibs.  per  square  inch,  was  used 
for  screw-bolts  approximately  one  inch  in  diameter,  and  the  harder  material, 
having  a  tensile  strength  of  G2,000  Ibs.  per  square  inch,  was  used  for  the 
screw-bolts,  which  were  reduced  to  approximately  one-half  inch  in  diameter. 
Four  such  bolts  were  made  of  each  of  these  sizes  for  each  of  the  four  styles 
of  thread  shown  in  Fig.  450,  making  in  all  32  bolts  with  screw-threads 


FIG.  450. 

which  were  tested.  Two  of  each  of  these  sets  were  tested  in  plain  tension, 
the  pulling  force  being  applied  to  the  inner  face  of  the  nut  at  one  end,  and 
increased  until  rupture  occurred.  The  other  two  bolts  of  each  set  were 
tested  also  in  tension,  but  under  a  torsional  action  resulting  from  the  con- 
tinuous turning  of  the  nut  as  the  load  increased  to  rupture.  In  this  case 
the  distortion  resulting  from  the  permanent  elongation  of  the  bolt  was 
nearly  all  taken  up  by  the  movements  of  the  testing-machine,  the  distortion 
taken  up  by  the  turning  of  the  nut  being  the  least  possible  to  maintain  a 
continuous  torsional  action  at  this  point. 

The  same  bars  were  also  tested  as  plain  tension-test  specimens  with  cylin- 
drical bodies,  and  again  with  grooves  turned  into  them  of  the  same  shape  as 

*  See  The  Locomotive  for  Nov.  1890  for  a  full  discussion  of  quadruple-riveted,  double- 
butt-strap  joints  having  an  efficiency  of  95  per  cent, 

f  At  the  request  of  the  German  Society  of  Civil  Engineers,  The  results  were  pub- 
lished in  Zeits.  d.  Ver.  Deutsch.  Ing.  for  April  27,  1896.  The  abstract  here  given  was 
made  by  the  author  and  published  in  the  Digest  of  Physical  Tests  for  July  1896. 


THE  STRENGTH  OF  STEEL. 


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536  THE  MATERIALS  OF  CONSTRUCTION. 

the  corresponding  screw-threads,  leaving  the  same  diameter  at  the  bottom 
of  the  groove  as  obtained  at  the  base  of  the  threads.  The  actual  and  com- 
parative average  results  of  all  of  these  tests  are  given  in  the  following  table, 
from  which  the  following  conclusions  may  be  drawn: 

1.  When  subjected  to  plain  tension  both  the  screw-threads   and  the 
grooved  sections  were  stronger  than  the  plain  bars  of  the  same  net  area  of 
cross-section,  this  excess  of  strength  having  an  average  value  of  about  14  per 
cent.     This  excess  of, strength   is  due  to  the  re-enforcing  action  of  the 
shoulder  in  the  case  of  the  groove,  and  of  the  threads  themselves  in  the  case 
of  the  screw. 

2.  There  is  no  very  marked  difference  in  the  average  strength  of  the 
bolts  on  which  the  several  styles  of  thread  were  cat,  the  perfectly  sharp 
groove  shown  at  A  being  slightly  stronger  than  the  others. 

3.  The  weakening  effect  of  the  turning  of  the  nut  under  stress  at  rup- 
ture is  much  less  than  might  have  been  predicted,  when  the  distortion  of 
the  screw  below  the  nut  by  permanent  elongation  is  taken  into  considera- 
tion.    The  tests  indicate  for  this  case  a  strength  of  the  one-inch  bolts  about 
20  per  cent  less  than  that  of  the  plain  bars,  and  of  the  one-half-inch  bolts 
about  15  per  cent  less  than  that  of  the  plain  bars. 

4.  In  general  it  may  be  said  that  the  turning  of  the  nut  upon  the  bolt  at 
rupture  reduces  the  strength  of  the  net  section  of  the  bolt  by  about  30  per 
cent. 

5.  It  is  very  probable  that  the  four  forms  of  screw-threads  here  shown 
would  show,  very  different  results  under  fatigue  tests  from  repeated  stresses, 
and  also  for  static  loads  on  high-carbon  steel.     Under  repeated  loads  and 
under  shock  it  is  probable  that  the  sharp  re-entrant  angle  shown  in  Fig.  450  A 
would  develop  incipient  cracks  much  earlier  than  either  of  the  other  forms, 
and  that  probably  the  Whitworth  thread,  shown  in  B,  would  be  the  last 
to  develop  this  kind  of  weakness,  either  with  soft  metal  under  repeated  loads 
or  with  high-carbon  steel  under  static  loads.     No  such  tests  have  as  yet  been 
made.     It  is  to  be  hoped  that  this  subject'  will  soon  be  investigated,  as  it  is 
of  far  more  importance  than  the  mere  matter  of  static  strength. 


CHAPTER  XXVII. 
THE  FATIGUE   OF  METALS. 

383.  Fatigue  Defined. — It  has  been  found  from  experiment  that  metals 
will  fail  under  loads  much  less  than  their  ultimate  strength  when  such  loads 
are  repeated  or  reversed  many  thousands  or  perhaps  millions  of  times.     It 
has  been  commonly  supposed   that  these  repetitions  or  reversals  caused   a 
general  deterioration  of  the  metal  so  stressed,  so  far  as  its  cohesion  is  con- 
cerned, which  deterioration  has  been  known  by  the  term  fatigue.     It  is  now 
known,  however,  that  no  such  general  deterioration  takes  place,  but  that 
some  of  the   millions  of  incipient  defects  or  "micro-flaws"  in  the  spec- 
imen gradually  extend  their  weakening  influence,  in  an  irregular  plane  of 
cross-section,  which  ultimately  becomes  the  plane  of  rupture,  while  the  metal 
immediately  adjacent  to  this  plane  remains  perhaps  wholly  uninjured.     In 
fact  no  tests  of  metal,  on  specimens  as  closely  adjacent  to  such  planes  of 
rupture  as  it  is  possible  to  procure  them,  have  ever  shown  any  deteriorating 
effects  of  the  repetitions  or  reversals  of  stress  to  which  this  metal  had  been 
subjected.     The  word  "  fatigue,"  therefore,  is  scarcely  the  proper  term  to 
apply  to  this  class  of  failures.     The  gradual  fracture  of  metals  would  be  a 
more  truly  descriptive  term  to  use. 

384.  The  Micro-flaws  in  Steel  have  been  studied  exhaustively  by  Mr. 
Thos.  Andrews,  F.R.S.,  M.  lust.  C.E.  of  Sheffield,  England,  and  described 
in  Engineering  of  July  10,  17,  and  24,  189G.     Some  of  his  illustrations  are 
here  reproduced  in  Fig.  451.     The  large  flaws  in  Nos.  3,  4,  5,  and  6  are 
due  to  small  blowholes,  while  the  dark  intercellular  spaces  in  Nos.  1  and  2 
are  largely  composed  of  the  sulphide  of  iron,  which,  so  far  as  it  destroys  the 
continuity  of  the  crystals,   makes'  the  iron  weak  and  brittle.     These  and 
similar  incipient  faults,  of  which  there  are  probably  scores  in  every  square 
inch  of  any  iron  or  steel  cross-section,  are  doubtless  the  initial  cause  of  the 
weakness  developed  by  repeated  loadings.     These  breaks  in  the  continuity 
of  the  metal  cause  the  stress  to  be  concentrated  at  their  edges,  and  the  con- 
stant variation  of  this  stress,  near  or  at  the  elastic  limit,  with  its  accompany- 
ing molecular  movements,  gradually  extends  the  fracture.     Evidently  there 
can  be  no  regularity  of  action  of  such  causes,  and  hence  no  very  rigid  rule  or 
law  for  such  failures.     Even  two  specimens  cut  from  the  same  bar  may  act 
very  differently,  to  say  nothing  of  specimens  made  by  the  same  processes  at 

537 


538 


THE  MATERIALS  OF  CONSTRUCTION. 


1.  Micro-flaws  x  250  ;  Sulphur 
=  0.25  percent. 


2.  Micro-flaws  X  200  ;  Sulphur 
=  2.00  per  cent. 


3.  Micro-flaws  X  250.     Siemens- 
Steel  Boiler-plate. 


4.   Micro-flaws  x  *J50.     Siemens  - 
steel  Propeller-shaft 


5.  Micro-flaws  x  400.     Bessemer-  6.  Micro-flaws  X  250.     Bessemer- 

steel  Railway-axle.  steel  Rail. 

FIG.  451. — Views  of  Internal  Micro-flaws  in  Steel.     (Andrews  in  Engineering,  July  1CV 

1896.) 


THE  FATIGUE  OF  METALS. 


539 


different  times  and  at  different  works,  or  of  specimens  made  by  different 
processes  and  having  different  chemical  compositions.  Evidently  the  results 
of  fatigue  tests  would  be  extremely  various,  and  this  is  the  experience  of  all 
the  experimenters  in  this  field  of  investigation. 

385.  Wohler's  Tests. — The  first  systematic  study  of  the  fatigue  of  metals 
was  made  by  Wohler  from  1849  to  1870  for  the  German  government,  and 

L 


U 
FIG.  452. — Wohler's  Machine  for  Repetitions  of  Tensile  Stress. 

these  were  continued  after  his  death  by  Spangenberg.     As  Wohler's  tests 
have  become  historically  famous,  his  appliances  are  here  described. 

For  Repeated  Tensile  Stresses  Wohler  used  the  apparatus  shown  in  Fig. 
<±52.     Here  the  specimen  A  is  stressed  through  the  lever  L  and  spring  s 


FIG.  453. — Wohler's  Machine  for  Repetition  of  Bending  Stress. 

acting  on  the  auxiliary  lever  m.  The  pull  of  the  spring  s  is  measured  by 
the  starting  of  the  adjusted  calibrated  spring  s'  through  the  terminal  lever  g. 
The  nut  at  the  rod  d  is  adjusted  to  give  the  minimum  load  on  the  spring  s 
by  starting  the  spring  s'  when  adjusted  tp  a  particular  tension,  and  the  cam- 
movement  of  d  to  its  extreme  downward  position  is  made  to  give  the  requi- 
site maximum  stress  in  the  specimen  by  adjusting  the  spring  s'  so  as  just 


540 


THE  MATERIALS  OF  CONSTRUCTION. 


to  lift  at  this  position  of  d.  The  rod  is  adjustable  by  means  of  a  turn- 
buckle.  In  this  way  .the  bar  A  can  be  stressed  in  tension  between  any  chosen 
limits. 

For  Repeated  Bending  Stresses  Wohler  employed  the  machine  shown  in 
Fig.  453.  Here  the  specimen  A  is  bent  downwards  by  the  adjustable  rod  q 
attached  to  the  rocking  lever  below.  If  the  load  is  not  to  be  wholly  removed 
each  time,  a  residual  deflection  is  maintained  by  means  of  the  abutting  screw 
in  the  lever  m.  Both  the  maximum  and  the  minimum  loads  are  fixed  by 
means  of  the  calibrated  spring  s  acting  on  the  attached  lever  g. 

For  Reversals  of  Bending  Stress  Wohler  made  use  of  the  apparatus 
shown  in  Fig.  454.  Here  two  test-bars  AA  are  attached  by  a  driving  fit  to 


FIG.  454. — Wohler's  Machine  for  Reversals  of  Bending  Stress. 


the  central  axle,  which  is  rotated  by  a  belt  and  pulley.  The  ends  of  the 
test-bars  are  held  down  by  the  calibrated  springs  ss,  so  that  the  bending 
stresses  are  reversed  at  every  revolution.  Of  course  the  test-specimens  are 
trued  up  to  run  truly  after  driving  and  before  loading. 

For  Repetitions  of  Torsional  Stress  Wohler  devised  the  machine  shown 
in  Fig.  455.     Here  the  specimen  A  is  fastened  to  the  moving  lever  L  at  one 


FIG.  455.  —Wohler's  Machine  for  Itepetition  of  Torsional  Stress. 


end  and  to  the  resisting  levers  hh  at  the  other.     The  lever  L  is  actuated  by 
the  connecting-rod  I  and  the  lever  0,  which  in  turn  is  moved  by  the  recip- 


THE  FATIGUE  OF  METALS. 


541 


rocating-bar  C.  If  the  bar  is  stressed  in  opposite  directions,  then  both  the 
levers  g  and  g'  are  in  use,  and  the  calibrated  springs  ss  act  to  limit  the  tor- 
sional  moment  to  the  required  amount  as  before. 

386.  The  Results  of  Fatigue  Tests. — The  most  careful  and  complete  set 
of  fatigue  tests  under  repeated  stresses  was  made  by  Bauschinger.  His 
results  on  mild-steel  plates  are  shown  in  Fig.  456.  For  this  material,  which 
had  an  ultimate  strength  of  64,000  Ibs.  per  square  inch  the  repetition  limit 
was  found  to  be  about  35,000  Ibs.  per  square  inch,  or  about  the  elastic  limit 


1 


7777^/K 


/N  A//< 


0  /  2  3  4  5  <?  7 

FIG.  456. — Bauschmger's  Fatigue  Tests  on  Mild-steel  Plates  under  Tensile  Stress  Re- 
peated from  Zero.     Attached  figures  indicate  number  of  tests  averaged. 

of  the  material.  This  material  was  very  uniform  in  quality  and  gave  quite 
consistent  results.  In  general  the  results  of  such  tests  are  very  discrepant, 
as  should  be  anticipated  from  the  nature  of  the  causes  operating  to  produce 
the  final  fracture. 

In  Fig.  457  are  given  the  results  of  a  series  of  tests  by  reversed  bending 
stress  on  various  grades  of  steel  and  on  cold-rolled  wrought-iron  bars.  As 
the  steel  bars  seemed  to  give  way  under  about  the  same  stresses,  irrespective 
of  their  several  elastic  limits  and  ultimate  strengths,  they  have  here  all  been 
averaged  to  bring  them  into  comparison  with  the  tests  on  the  wrought-iron 
bars.  These  results  seem  to  be  favorable  to  wrought  iron  rather  than  to  this 
particular  kind  of  steel.  As  both  the  phosphorus  arid  sulphur  were  pretty 
high  in  all  these  steel  bars  (see  Figs.  76  and  451),  the  weakening  effects  of 
these  may  account  for  the  relatively  poor  showing  of  steel  in  this  series  of 
tests.  There  is  no  doubt,  however,  that  the  best  grades  of  wrought  iron  have 
this  advantage  over  steel,  that  an  incipient  fault  or  fracture  does  not  so 
readily  extend  itself  across  the  section,  but  is  more  likely  to  be  stopped  by 
the  slag  impurities  which  separate  the  filaments.  In  the  more  homogeneous 
and  more  perfectly  crystallized  steel  a  micro-flaw  more  readily  extends 
throughout  the  section. 

387.  Limits  of  Maximum  and  Minimum  Stresses  for  an  Indefinite  Number 
of  Repetitions.— Wohler's   tests   revealed   the  fact   that  for  an  indefinite 


542 


THE  MATERIALS  OF  CONSTRUCTION. 


number  of  repetitions  of  the  maximum  load  this  maximum  itself  could  be 
increased  if  a  portion  of  the  stress  were  left  on.  Thus  his  tests  on  spring- 
steel,  which  had  a  static  tensile  strength  of  124,000  Ibs.  per  square  inch,  gave 
results  as  plotted  in  Fig.  458.  When  the  load  was  wholly  removed  each 
time,  the  maximum  load  which  could  be  repeated  many  millions  of  times 


was  67,000  Ibs.  per  square  inch,  which  is  marked  pl  in  the  figure.  When 
24,000  Ibs.  stress  per  square  inch  remained  on  each  time,  the  maximum 
load  could  be  raised  to  75,000  Ibs.  per  square  inch,  and  repeated  an  un- 
limited number  of  times.  When  there  was  35,000  Ibs.  stress  left  on,  the 
maximum  load  could  be  raised  to  86,000  Ibs.  per  square  inch;  when  the 


THE  FATIGUE  OF  METALS. 


543 


minimum  was  56,000  Ibs.  the  maximum  was  96,500  Ibs.,  and  when  the  mini- 
mum was  70,000  Ibs.  per  square  inch  the  maximum  could  be  raised  to 
108,000  Ibs.  per  square  inch,  with  an  indefinite  number  of  repetitions.*  In 


/ 


/zqffw 


fftp00 


^ 

.si. 


m 


f 


FIG.  458. — Results  of  Wobler's  Fatigue  Transverse  Tests  on  Spring-steel.     The  shaded 
area  is  the  field  in  which  the  material  may  be  worked  indefinitely. 

Fig.  458  these  minimum  values  are  plotted  upon  a  straight  inclined  line,  and 
the  corresponding  maximum  values,  plotted  to  the  same  scale,  fall  in  the 
broken  dotted  line. 

These  and  many  other  similar  series  of  tests  on  other  grades  of  steel  and 
on  wrought  iron  led  to  a  formula  by  Launhardt  which  may  be  written 


(1) 


*  See  also  Wohler's  results  in  Unwin's  Testing  of  Materials  of  Construction,  p.  368. 


544 


TEE  MATERIALS  OF  CONSTRUCTION. 


in  which     m  —  maximum  stress; 

pi  =  "repetition  limit"  when  n  =  0; 
n  =  minimum  stress; 
f  —  ultimate  static  strength. 

The  locus  of  this  curve  is  given  as  a  full  line  in  Fig.  458,  and  the  area 
included  between  this  and  the  minimum  line  is  shaded,  and  may  be  consid- 
ered as  representing  the  field  across  any  part  of  which  this  material  could 
be  stressed  and  relieved  an  indefinite  number  of  times. 

388.  Limits  of  Maximum  and  Minimum  Stresses  when  these  are  of  Oppo- 
site Kinds. — When  the  stress  is  partly  or  wholly  reversed  an  indefinite 
number  of  times,  the  working  field  is  widened  and  the  upper  limit  cor- 
respondingly reduced.  This  condition  is  shown  in  Fig.  459,  the  limiting 


ff0000 


1-40000 


+34000 


+  20000 


/0000 


~/0000 


^ 

&      ;tl) 

^  f y 


N 


/770/V 


FIG.  459.— Typical  Fatigue  Diagram  of  Limiting  Stresses  for  60,000  Ibs.  Steel  for  an 
Infinite  Number  of  Repetitions  or  Reversals  of  Stress. 

case  being  when  the  stress  is  wholly  reversed  each  time,  when  the  minimum 
stress  numerically  equals  the  maximum  stress.  These  limits  are  marked 
and  —  p^  in  the  figure,  and  are  here  called  the  "reversal  limits."* 


*  These  terms,  repetition  limit  and  reversal  limit,  were  coined  by  the  author  for  these 
values  in  his  paper  on  this  subject  in  Jour.  Assoc.  Eng.  Socs.,  vol.  vn,  1888. 


THE  FATIGUE  OF  METALS.  545 

The  formula  for  the  value  of  the  larger  stress  in  terms  of  the  smaller,  and 
of  these  limits,  pl  and  p^  ,  was  proposed  by  Weyrauch,  and  is 


(2) 


The  loci  of  both  of  these  equations  are  drawn  in  Fig.  459,  and  the  working 
field  indicated  by  them  i&  shaded.  Here,  however,  the  material  is  supposed 
to  be  60,000-1  b.  structural  steel,  and  pl  is  taken  as  one  half  the  ultimate 
strength,  or  30,000  Ibs.  per  square  inch,  and  p9  as  one  third  the  ultimate 
strength,  or  20,000  Ibs.  per  square  inch,  these  being  about  the  values  of 
both  of  these  limits  as  determined  by  all  the  fatigue  tests  which  have  ever 
been  made. 

389.  A  New  and  Universal  Formula  for  Dimensioning.  —  As  shown  by 
Fig.  458,  a  straight  line  would  fairly  fit  the  observed  maximum  stresses  for 
the  given  minimum  stresses  when  these  also  are  plotted  on  a  straight  line. 
From  Fig.  459,  also,  it  would  seem  unreasonable  to  have  a  sudden  change  of 
law  when  the  minimum  stress  passes  through  zero.  Furthermore,  there  is 
no  theoretical  basis  for  the  particular  formulae,  (1)  and  (2),  which  give  these 
curves.  It  would  therefore  seem  to  be  more  rational,  and  fit  the  facts  quite 
as  well,  to  make  these  upper  limits  fall  into  a  straight  line,  as  shown  in  Fig. 
460.  By  so  doing  we  obtain  a  single  formula  for  both  repeated  and  for 
reversed  loads.,  whereas  now  two  formulae  are  employed.  To  derive  the 
formula  for  this  upper  limit  we  have,  from  experiment  : 

Static  load-limit  =  f  =  ultimate  strength; 
Repetition  limit  =  p1  =  -J  ultimate  strength" 
Reversal  limit      =  p^  =  %  ultimate  strength. 

Hence,  when  the  ultimate  limits  are  reduced  to  working  limits,  we  will 
suppose  that  p^  reduces  to  a,  Fig.  460,  and  all  other  parts  in  proportion, 
giving. 

Working  static-load  stress  =  2r/;  ^| 

Working  live-load  stress      =  a\     >•      .....     (3) 

Working  reversed  stress      =  fa.  J 

To  find  the  equations  of  the  total  working  stress  in  terms  of  the  maximum 
and  minimum  total  stresses  on  any  member: 

Let  L  =  total  live-load  stress  on  any  member; 
D=      "     dead-load     "      "     "  " 

A  =  area  of  cross-section  of  the  member; 
p  =  maximum  stress  in  the  member  per  square  inch  for  both  dead  and 

live  loads; 
a  =  working  stress  for  live  loads. 


546  THE  MATERIALS  OF  CONSTRUCTION. 

Then  we  have,  from  Fig.  460, 

nl  =  dead-load  stress  per  square  inch  =  — ; 
nm  =  live-load  stress  per  square  inch  =  — ; 
ml  =  total  stress  per  square  inch 


COMPRESSION 


/A/  c$Mf/?£SS/o/v=  - 

FIG.  460. 


And  since  rs  =  2a,  we  have,  from  the  figure, 




p  =  Op  =  Oa  -\-  Jim     and     hm  =  -=  (rs  —  Oa) ; 

rs 


D 


D 


THE  FATIGUE  OF  METALS.  547 


But  A  —  -       — ;  hence  we  have 


'(- 


-L) 
and  finally 


min.  stress 
2  max.  stress 

This  formula  may  be  used  in  place  of  both  Launhardt's  and  Weyrauch's 
equations  ((1)  and  (2) ),  since  it  applies  equally  well  to  stresses  of  the  same 
or  of  opposite  kinds,  by  paying  attention  to  the  sign  of  the  minimum  stress. 
When  the  minimum  stress  becomes  negative  the  sign  of  the  second  term  in 
the  denominator  changes  to  plus,  thus  reducing  p  below  a. 

Another  argument  in  favor  of  this  formula  lies  in  the  fact  that  it  is  the 
same  as  the  old  rule  of  using  twice  the  factor  of  safety  for  live  as  for  dead 
loads,  as  will  now  be  shown. 

With  the  same  notation  as  above,  we  have 

L       D  _  2L  +  D 

^7t+2a~    ~  2a     ' 
also 


Substituting  the  value  of  A,  we  have 


_  _  _  a  __  _  a 

2L  +  D  D  _      min.  stress  ' 

~  2(L  +  /))  ~  2  max.  stress 

We  find,  therefore,  that  the  past  practice  founded  on  experience,  and  the 
fatigue  experiments,  all  agree  and  are  all  expressed  in  this  one  formula  which 
is  universal  in  its  application  to  stresses  of  the  same  and  of  opposite  signs. 
Its  use  is  more  laborious  than  those  hitherto  used,  as  given  in  equations  (1) 
and  (2),  only  in  requiring  a  division  in  place  of  a  multiplication;  but  as  such 
work  is  now  done  wholly  by  the  slide-rule,  even  this  objection  is  removed. 


CHAPTER   XXVIII. 


STRENGTH  OF  THE  COPPER-ZINC-TIN  ALLOYS. 


COPPER. 

390.  Strength  of  Copper. — The  first  and  most  general  error  to  guard 
against  in  the  matter  of  the  strength  of  copper  and  its  alloys  is  that  of  ignor- 
ing the  mechanical  treatment  to  which  the  material  has  been  subjected. 
Thus  in  the  case  of  copper  plate,  as  shown  by  Fig.  461,  a  hot-rolled  plate 
has  an  elastic  limit  of  only  some  7000  or  8000  Ibs.  per  square  inch,  with  an 
elongation  of  50  per  cent,  while  the  same  plate,  cold-hammered,  has  an 
elastic  limit  of  over  20,000  Ibs.  per  square  inch,  with  an  elongation  of  30  per 
cent.  Both  have  an  ultimate  strength  of  about  33,000  Ibs.  per  square 


5      /0     /5     2O    25    30     35 

FIG.  461.— Typical  Stress  diagrams  of  Copper  Plate  £  in.  thick. 
(Martens,  Berlin  Testing  Lab.  Communications,  1894.) 

inch.  When  simply  cast,  without  rolling  or  forging,  both  the  elastic  limit 
and  the  ultimate  strength  are  much  less,  but  copper  is  seldom  or  never  used 
in  this  way. 

Drawn  copper  wire  has  an  elastic  limit  of  about  25,000,  with  an  ultimate 
strength  of  some  35,000  Ibs.  per  square  inch,  as  shown  in  Fig.  462,  with  an 
elongation  of  about  30  per  cent. 

If  the  strength  of  copper  be  computed  on  the  actual  section  at  all  stages 
of  the  test,  and  if  the  strength  so  computed  be  plotted  to  the  diminishing 
cross-section,  the  results  will  plot  in  a  straight  line,  as  shown  in  Fig.  463. 

548 


STRENGTH  OF  THE  COPPER- ZINC- TIN  ALLOYS. 


549 


FIG.  462.— Typical  Stress-diagram  of  Drawn  Copper.     ( Wat.  Ars.  Rep.  1886, 

vol.  ii.  p.  1673.) 


70,000 


SQ000 


~24     22      2O       /8      '/<?      /4 

FIG.  463. — Showing  a  Linear  Relation  b  \  \\-wn  Reduction  of  Area  of  Section  ana  Stress 
per  Square  Inch  of  Actual  Suction  of  Rolled  Copper  Plate  i  inch  thick.  (Rep  Fr* 
Com.,  vol.  in,  PI.  VI.) 


550 


THE  MATERIALS  OF  CONSTRUCTION. 


That  is  to  say,  when  copper  is  cold-drawn,  its  strength  per  square  inch 
regularly  increases  up  to  rapture,  when  its  strength  per  square  inch  of  actual 
section  is  some  70,000  Ibs.  per  square  inch. 

391.  Annealing  or  Softening  Hard-drawn  Copper  Wires  or  Plates. — 
Unlike  steel,  copper  is  softened  by  quenching  in  water  from  a  sufficiently  high 
temperature.  The  softening  effect  is  due,  however,  rather  to  the  tempera- 
ture attained  than  to  the  manner  of  cooling.  At  least  the  sudden  cooling 
does  not  prevent  the  softening.  The  annealing  temperature  is  about 
750°  F.,  as  shown  in  Fig.  404. 


0 


wtg@0t§[w§0#s(ffltf( 

0/23 

FIG.  464. — Effects  of  Heating  to  given  Temperatures,  and  then  Quenching  in  Water. 
Hard-drawn  Copper  Wires.     (Martens,  Berlin  Testing  Lab.,  1894,  PI.  I.) 


392.  The  Strength  of  Brass.  —  Brass  is  an  alloy  of  copper  and  zinc.  The 
mechanical  properties  of  all  possible  compositions  are  given  in  Fig.  465, 
these  applying  in  a  general  way  to  cast  forms  only.  .Either  hot  or  cold  forg- 
ing or  rolling  will  greatly  change  these  properties.  Thus  the  strength  of 
very  hard-drawn  brass  wire  or  hard-rolled  brass  plate  may  have  a  tensile 
strength  of  over  60,000  Ibs.  per  square  inch,  with  an  elastic  limib  about  the 
same,  as  shown  in  Fig.  466.  Annealed  brass  plates  or  wires,  however,  have 
an  elastic  limit  of  only  about  10,000  Ibs.  per  square  inch. 

Brass  is  much  harder  than  copper,  as  shown  in  Fig.  465,  by  the  "  crush- 
ing strength  "  diagram,  this  rising  from  28,000  Ibs.  for  100  per  cent  copper 
to  120,000  Ibs.  per  square  inch  for  50  per  cent  copper.  It  is  this  property 
of  increased  hardness  which  makes  brass  so  much  more  useful  than  copper 
in  the  arts.  The  conductive  capacity  of  brass  is,  however,  much  less  than 
that  of  pure  copper,  it  falling  from  0.90  for  pure  copper  to  0.20  for  70  per 
cent  copper. 


STRENGTH  OF  THE  COPPER-ZING-TIN  ALLOYS.  551 

VS00000O 


iGr.  465. — Properties  of  Cast  Brass  for  Varying  Proportions  of  Copper  and  Zinc.  The 
"  composition  "  argument  gives  the  proportions  of  copper.  (Data  from  U.  £  Test 
Board  Rep.  1881,  vol.  u.) 


70.000 


FIG.  466 — Stress-diagrams  of  Rolled  Plate  of  Brass  and  Copper,  having  the  Composition 
Cu  67,  Z  33.     (Fr.  Com.  Rep.,  vol.  m,  PI.  V.l 


552 


THE  MATERIALS  OF  CONSTRUCTION. 


The  most  generally  useful  brass  composition  is  from  60  to  70  per  cent 
copper  and  40  to  30  per  cent  zinc,  as  is  fully  shown  by  Fig.  465. 

By  rolling  to  thin  plates,  especially  by  cold-rolling,  the  strength  of  brass 
may  be  greatly  increased  at  the  expense  of  the  ductility.  The  simultaneous 
qualities  of  strength  and  ductility  which  may  be  expected  from  brass  which, 
in  the  form  of  a  casting,  has  a  tensile  strength  of  35,000  Ibs.  per  square  inch 


earn 


V£VT  6 


Z/A 


V&AT/0.V 


0   /0  20  3$  40' J0  £070 

FIG.  467.— Showing  the  Relation   between  the   Ultimate  Strength  and  the  Ultimate 
Elongation  of  Brass.     (Fr.  Com.  Rep.,  vol.  in,  PI.  V.) 

and  an  elongation  of  nearly  40  per  cent  are  given  in  Fig.  467.  Thus  in  a 
ribbon  J  in.  x  ^  in.  in  cross-section  the  strength  is  45,000  Ibs.  per  square 
inch  with  60  per  cent  elongation;  60,000  Ibs.  with  15  per  cent  elongation; 
and  90,000  Ibs.  with  3  per  cent  elongation. 

393.  The  Strength  of  Bronze. — The  ultimate  tensile  strength  of  all  possi- 
ble compositions  of  copper,  zinc,  and  tin,  in  the  form  of  unworked  castings, 
is  given  in  Fig.  468.*  This  is  similar  to  that  first  published  by  Dr.  Thurs- 


*  This  is  the  same  as  Fig.  76,  which  is  repeated  here  for  convenience. 


STRENGTH  OF  THE  COPPER-ZING-TIN  ALLOTS. 


553 


ton,  but  his  was  constructed  from  torsion  tests,  while  this  is  made  wholly 
from  tension  tests.  It  is  the  property  of  any  equilateral  triangle  that  the 
sum  of  the  normals  from  any  point  in  it  to  the  three  sides  is  equal  to  the 
common  altitude  of  the  triangle.  Hence  if  these  altitudes  be  each  made  to 
represent  percentages,  from  zero  to  100,  and  so  graduated,  each  starting 
with  100  at  the  apex  and  reducing  to  zero  at  the  opposite  base,  these  may 
each  represent  a  scale  of  one  of  the  three  ingredients,  copper,  zinc,  and  tin. 


T//V  Z//VC 

FIG.  468.— Showing  the  Tensile  Strength,  in  Pounds  per  Sq.  Inch,  of  All  Possible  Com- 
binations of  Copper,  Tin,  and  Zinc,  in  the  Form  of  Unrolled  or  Uuforged  Castings. 
(Compiled  by  the  Author  from  the  Records  of  the  U.  S.  Test  Board  1881.) 

which  go  to  make  up  all  the  bronzes.  By  drawing  lines  through  these  points 
of  division  in  the  altitudes,  parallel  to  the  bases,  the  triangle  is  subdivided 
into  a  series  of  similar  smaller  triangles  as  shown  in  Fig.  468.  Any  possible 
composition  of  copper,  tin,  and  zinc,  each  represented  as  a  certain  per- 
centage of  the  whole,  may  now  be  represented  graphically  by  a  location  on 
this  diagram.  Its  normal  distances  from  each  of  the  three  sides,  read  off  on 
the  section  lines  in  percentages,  are  at  once  the  percentages  of  these  three 
ingredients  in  that  composition,  the  sum  of  these,  of  necessity,  always 
being  100. 


554 


THE  MATERIALS  OF  CONSTRUCTION. 


J03  .004  .00S  .00$  .007 


00000 


3000 


40000- 


3000- 


24000 


**t 


.004  . 


.0/0 


FIG.  469.— "Results  of  Tension  and  Compression  Tests  on  Three  Alloys  used  for  Valve- 
stems.  Tobin  bronze  rolled,  others  plain  castings.  (Russell,  Jour.  Assoc.  Eng.  Socs., 
vol.  xv,  p.  207.  Tests  made  by  the  Author.) 


70000 


00000 


S0.000 


40000 


20000 


/0000 


a, 


Pi 


WfiWAtt//* 


OF 


1AT/OV 


0  £  /0          /£         20         2S        30       35 

FIG.  470.— Tension  Stress  diagrams  of  Cast  and  Rolled  Bronzes.     (Wat.  Ars.  Rep.  I8S5.) 


STRENGTH  OF  THE  COPPER-ZINC-TIN  ALLOYS. 


555 


£  [IMPOSITION  OF  SPECIMENS', 


0 

0  5 

FIG.  471. — Tension   Stress-diagrams  of  Aluminum  Bronze  of  Various  Compositions. 
Cast  in  a  chilling  and  in  dry-sand  moulds.    (Wat.  Ars.  Hep.  1888.) 


t 

/00,000 

80.000 
60,000 
40.000 
20.000 

I 

7       20      40        60       SO 

^ 

W 

W 

: 

^j 

-LOyG: 

K 

^C 

^ 

1 

^ 

^ 

g 

-•  • 

r\'c 

/T^ 

"~xw 

•  - 

•; 
^ 

•% 

•^ 

', 

> 

\'~; 

§ 

i 

^ 

1 

e 

| 

-^ 

k 

'A 

I 

1 

T& 

yp\ 

'Rt 

TU, 

?l 

^       200°  400°    600'  M 

FIG.  472. — Strength  of  Aluminum  Bronze  at  Various  Temperatures  and  for  Various 

Percentages  of  Elongation. 


o56  THE  MATERIALS  OF  CONSTRUCTION. 

From  an  examination  of  this  chart  it  is  at  once  evident  that  only  those 
alloys  near  the  copper  apex  are  of  any  value,  the  strongest  being,  however, 
near  the  copper- zinc  side,  where  the  composition  is  about  59  per  cent  copper, 
39  per  cent  zinc,  and  2  per  cent  tin.  The  tensile  strength  of  such  a  casting, 
if  properly  made,  is  about  00,000  Ibs.  It  is  too  brittle,  however,  to  be  of 
much  value.  The  most  valuable  alloys  are  those  having  an  ultimate  strength 
of  from  35,000  to  40,000  Ibs.  tensile  strength,  this  having  from  20  to  30 
per  cent  elongation.  This  is  found  in  the  vicinity  of  75  to  85  per  cent 
copper,  1?  to  5  per  cent  zinc,  and  8  to  10  per  cent  tin. 

Tobm  Bronze  is  simply  such  a  composition  as  the  above  hot-rolled  after 
casting.  The  effect  of  this  rolling  is  to  greatly  increase  both  the  strength 
and  the  ductility,  as  shown  by  Fig.  469.*  This  material  is  in  almost  every 
respect  similar  to  soft  steel,  so  far  as  its  mechanical  qualities  are  concerned. 
It  has  the  further  advantage  of  not  corroding  under  ordinary  conditions, 
hence  its  extraordinary  value  as  a  structural  material.  The  author  has  seen, 
however,  some  very  remarkable  and  unexplained  fractures  of  this  material 
which  leads  him  to  suspect  its  reliability. 

Phosphor-bronze  has  no  special  mechanical  properties  other  than  marks 
all  good  bronzes  (see  Fig.  470).  Phosphorus  is  used  to  destroy  the  effects 
of  oxidation  in  melting  rather  than  to  add  to  the  strength  or  ductility  other- 
wise. In  destroying  these  oxides  it  does  improve  the  product;  but  if  the 
melting  is  performed  in  such  a  way  as  to  prevent  oxidation,  there  is  no  need 
of  the  phosphorus. 

394.  Aluminum-bronze  may  have  great  strength  in  Doth  the  cast  and 
the  rolled  forms,  as  shown  in  Fig.  471,  where  many  tests  on  different 
compositions  and  from  different  kinds  of  moulds  are  plotted  from  the  same 
origin.  The  effect  of  the  rolling  in  increasing  the  strength  and  the  ductility 
is  evident.  A  small  percentage  of  aluminum  is  thus  seen  to  greatly  improve 
the  bronze  although  its  strength  alone  is  very  small,  as  is  also  shown  in  this 
figure. 

*  The  total  elongation,  which  was  over  30  per  cent,  is  not  shown  in  this  figure.    • 


CHAPTER   XXIX. 

THE  EFFECTS  OF  TEMPERATURE  ON  THE  MECHANICAL  PROPERTIES 

OF  METALS. 

EFFECTS   ON   IRON   AND   STEEL. 

395.  As  Shown  by  Stress-diagrams. — This  subject  has  been  very  fully 
and  carefully  investigated  at  the  testing  laboratory  of  the  U.  S.  Arsenal  at 
Watertown,  Mass.,  and  a  full  series  of  diagrams,  similar  to  that  shown  in 


60000 


70000 


02        4         6         8/0/2/4/3/8 

FIG.  473.- Stress-diagrams  of  Steel  Bars,  0.20$  Carbon,  0.45#  Manganese,  at  Various 
Temperatures.     (Wat.  Ars.  Rep.  1888.) 

Fig.  473,  is  given  in  the  report  for  1888.  The  curves  in  this  figure  exhibit 
the  action  of  0.20  per  cent  carbon  steel,  having  a  normal  tensile  strength  at 
70°  F.  of  70,000  Ibs.  per  square  inch,  with  a  normal  elastic  limit  of  some  37,000 
bis.  per  square  inch.  Fig.  473  reveals  both  the  elastic  limit  and  the  ultimate 

557 


558 


THE  MATERIALS  OF  CONSTRUCTION. 


strength,  both  of  which  are  above  the  normal  at  0°  F.,  and  below  the  normal 
at  210°  F.  The  ultimate  strength  then  increases  with  a  rising  temperature, 
reaching  a  maximum  at  about  600°  F.,  from  which  temperature  it  regularly 


200  400  6W  80O 

FIG.  474.— Variation  of  Tensile  Strength  with  Temperature.     (Wat.  Ars.  Pep.  1888. 


/00°         £00°       <30O0        400°        300°        600°        700°       <%X? 
FIG.  475. — Variation  of  Tensile  Strength  of  Wrought  Iron  <iml  Steel  for  Varying  Tem- 
peratures.    Cornell  University  Tests.     (Jour.  West.  Soc.  Engrs.,  vol.  I.) 

diminishes  in  ultimate  strength,  reaching  00,000  Ibs.  at  800°  F.,  50,000  Ibs. 
at  960°  F.,  40,000  Ibs.  at  1050°  F.,  30,000  Ibs.  at  1150°  F.,  20,000  Ibs.  at 
1400°  F.,  and  10,000  Ibs.  at  1570°  F.  These  simultaneous  values  are  better 


EFFECTS  OF  TEMPERATURE  ON  METALS. 


559 


read  off  from  Fig.  474  than  from  Fig.  473.  In  the  former,  also,  are  found 
the  variations  of  the  ultimate  strength  of  all  grades  of  steel,  and  of  wrought 
and  cast  iron. 

Returning  now  to  Fig.  473,  it  will  be  seen  that  the  elastic  limit  regularly 
and  continuously  diminishes  from  the  zero  temperature,  where  it  is  some 
42,000  Ibs.  per  square  inch,  the  metal  becoming  regularly  more  plastic  as 
the  temperature  rises.  This  is  also  shown  in  Fig.  478. 

Jn  Fig.  476  we  see  the  relative  effects  of  slow  and  rapid  applications  of 


SLOWLQAO/N& 

MP/OAMffMG 


-300"   400°    500"    6M°    70O'    800     3M    MKr  //00T: 
FIG.  476. — Ultimate  Tensile  Strength  of  Steel  and  Wrought  Iron  at  Temperatures 
between  Freezing  and  1000°  F.  for  Slow  and  Rapid  Loading.     (Fr.  Com.  Rep., 
vol.  n,  PL  XX.) 

the  load  on  wrought  iron  and  steel  at  different  temperatures.  At  ordinary 
temperatures  the  quick  loading  develops  a  greater  ultimate  tensile  strength 
than  the  slow  loading.  Between  250°  and  700°  F.  for  steel,  and  between 
150°  and  500°  F.  for  wrought  iron,  the  quick  loading  gives  a  less  ultimate 
strength,  while  beyond  these  higher  temperatures  the  quick  loading  again 
gives  the  greater  strength. 


80000 


0000 
60000 


50000 


40000 


SQ000 


¥- 


T^IG.  477. — Tension  Tests  of  Soft  Steel  Wire  at  Temperatures  from  —  90°  to  -(-  200°  F. 
for  Different  Rates  of  Loading.     (Fr.  Com.  Rep.,  vol.  u,  Plate  XX.) 

Similar  effects  are  shown  in  Fig.  477  for  soft  steel  wire,  for  both  the 
ultimate  strength  and  the  yield-point  or  apparent  elastic  limit,  for  tempera- 
tures between  —  90°  and  -f  200°  F. 


560 


THE  MATERIALS  OF  CONSTRUCTION. 


396.  The  Change  in  the  Elastic  Limit  is  by  far  the  most  important  of 
all  the  changes  produced  by  rising  temperatures,  so  far  as  structural  use  is 
concerned.  Commonly  only  the  ultimate  strength  is  given  for  rising  tem- 
peratures, and  as  this  increases  up  to  500°  or  600°  F.,  it  is  assumed  that  the 
working  strength  increases  also.  That  this  is  not  the  case  is  shown  for  one 
grade  of  steel  in  Fig.  473,  and  for  all  grades  of  steel  combined  in  Fig.  478. 
Here  the  "  mean  variation  in  the  elastic  limit  "  curve  continuously  descends 


#00 


FIG.  478.— Grand  Mean  Curves  from  Temperature  Tests  on  Steel  Rods  0.8  in.  in  diam- 
eter, turned  from  1^-in.  rods,  of  ten  different  degrees  of  hardness,  from  0.09#  to 
0.97$  C.  (Wat.  Ars.  Rep.  1888,  p.  245.) 

from  a  zero  temperature,  the  mean  results  falling  almost  exactly  in  a  smooth 
curve,  which  is  nearly  a  straight  line,  while  the  "  mean  ultimate  strength  " 
curve  has  a  minimum  point  at  '200°  F.  and  a  maximum  point  at  500°  F., 
after  which  it  regularly  decreases  also.  Thus  at  500°  F.  the  mean  ratio  of 
elastic  limit  to  ultimate  strength,  for  all  grades  of  steel,  is  only  0.36,  while 
at  ordinary  temperatures,  from  zero  to  100°  F.,  it  is  0.57,  as  shown  by  Fig. 
478. 

For  structural  purposes,  therefore,  the  working  strength  of  wrought  iron 
and  steel  must  be  regarded  as  regularly  diminishing,  while  the  temperature 
increases,  the  rate  of  diminution  being  about  4  per  cent  for  each  100°  F. 
increase  in  temperature. 

Similar  curves  in  Fig.  479  do  not  indicate  this  uniform  reduction  from 
a  zero  temperature,  but  they  are  not  based  on  as  extensive  a  series  of  tests  as 
those  summarized  in  Fig.  478. 


EFFECTS  OF  TEMPERATURE  ON  METALS, 


561 


397.  The  Change  in  Ductility. — The  great  redaction  in  the  elongation 
of  wrought  iron  and  steel,  for  temperatures  from  100°  to  400°  F,,  with  a 


0V.   /00     200  300   400    /00 

WROUGHT  IRON.  OPEN-HEARTH  STEEL. 

FIG.  479.— Teusile  Properties  of  Wrought  Iron  and  of  Open-hearth  Steel  at  Various 
Temperatures  Centigrade.     (Berlin  Testing  Lab.  1893.) 

minimum  at  about  300°  F.,  is  a  remarkable  fact  which  could  not  have  been 
predicted.  Thus  wrought  iron  with  22-J-  per  cent  elongation  at  a  tempera- 
ture of  80°  F.  has  but  7  per  cent  elongation  at  300°  F.,  as  shown  in  FiX 


/£ 


(3) 


P  £  ff  J  ? 


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(2} 


<S  ,7 £  .?/A 


480,— Variatipn  in  the  Ductility  of  Wrought  Iron  and  Tool-steel  for  Varying  Tein* 
peratures.    Cornell  .University  Tests,    (Jour,  West,  Soc,  Engn,,  vol.  i.) 


662 


THE  MATERIALS  OF  CONSTRUCTION. 


480,  while  from  Fig.  479  a  32-per-cent  elongation  of  both  wrought  iron  and 
mild  steel  at  32°  F.  reduces  to  14  per  cent  at  300°  F.  Above  this  tempera- 
ture the  elongation  increases  again,  reaching  its  normal  amount  at  a  tempera- 
ture of  some  600°  F. 


FIG.  481. — Effect  of  Moderate  Temperatures  on  the  Modulus  of  Elasticity.     (  Wat.  Ars. 

Rep.  1887.) 

398.  The  Change  in  the  Modulus  of  Elasticity  is  shown  in  Figs.  479  and 
481.  In  all  cases  it  regularly  decreases  for  rising  temperatures,  except  that 
the  Berlin  tests  on  steel,  Fig.  479,  show  a  small  increase  in  the  modulus 

ZJ40 


k 


&4M 


Z 


/       ^      <?      4      <f      f 

FIG.  482.— Variations  in  the  Specific  Gravity  of  Steel  at  Different  Temperatures.  Each 
point  the  mean  of  six  observations,  the  carbon  varying  from  0.53^  to  1,08^. 
(Langley,  in  Am,  Gliem.,  1876.) 


EFFECTS  OF  TEMPERATURE  ON  METALS. 


563 


FIG.  483.- Hot  Tests  of  Wrought-iron  Car-axles.    Temp.  300°  F. 


FIG.  484.— Cold  Tests  of  Wrought  iron  Car-axles.    Temp.  -  18°  F. 

Impact  Tests  of  Car-axles,  4|  in.  in  Diameter,  showing  Characteristic  Fractures  at 
800°  F.  and  at  -  18'  "P.  (Thos.  Andrews,  M.  Tnat.  C.  E.f  before  the  Soc.  Engrs. 
(London),  1896,  in  a  Bessemer  Premium  Paper.) 


064 


THE  MATERIALS  OF  CONSTRUCTION. 


from  freezing  to  '200°  F.  Xo  such  effect  is  shown  in  Fig.  481.  In  general 
it  may  be  said  that  for  wrought  iron  and  steel  the  modulus  of  elasticity 
decreases  about  2  per  cent  for  each  100°  F.  increase  in  temperature. 

399.  Effect  on  Specific  Gravity. — This  is  shown  in  Fig.  482  to  be  quite 
uniform,  but  no  absolute  temperatures  Avere  determined.     We  can  only  say 
that  in  cooling  from  a  Avhite  heat  to  black  the  specific  gravity  increased  from 
7.70  to  7.8o,  an  increase  of  nearly  one  per  cent  variation  in  temperature.* 

400.  Effect  on  Resistance  to  Impact. — This  is  shown,  for  wrought-iron 
car-axles,  in  Fig.  485,  and  the  change  in  the  fracture  from  a  crystalline 
appearance  at  a  temperature  of  —  18°  F.  to  a  fibrous  appearance  at  300°  F. 
is  well  shown  in  Figs.  483  and  484.      The  minimum  toughness  is  found  at 
300°  C.  or  570°  F.,  which  agrees  substantially  with  the  temperature  of  maxi- 
mum ultimate  tensile  strength,  but  of  minimum  elongation.     This  could 
have  been  predicted  from  the  reduced  ductility  at  this  temperature.     The 
paper  here  cited  contains  a  great  many  photographic  reproductions  of  frac- 
tures from  which  those  in  Figs.  483  and  484  have  been  selected  as  character- 
istic.    They  are  all  very  much  alike. 

Mr.   Andrews's  impact  tests  of  wrought-iron  car-axles  at  zero  and  at 
100°  F.  show  a  great  difference  in  the  resistance  to  impact  even  for  this 


M 

25 
2$ 
/5 
fa 

5 
tf 

i 

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/ 

p 

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& 

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^ 

^~ 

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w^s/ 

747V, 

?£  0, 

-  '  JXi 

£3 

0°a  M0    200    300  400  300  #06 

FIG.  48"). — Endurance  Tests  of  Wrought-iron  Railway  axles  at  Varying  Temperatures 
Centigrade.  Axles  deflected  by  impact  and  then  turned  over  and  deflected  in  the 
opposite  direction.  (Andrews,  before  the  Soc.  of  Engrs.  (London),  1896.) 

small  variation  in  temperature.*  These  axles  were  4^  in.  in  diameter  and 
rested  on  supports  3|  ft.  apart.  They  were  tested  by  dropping  a  tup- 
weighing  2240  Ibs.  a  distance  of  30  in.,  the  axle  being  turned  over  after  each 
blow  and  its  temperature  restored,  until  it  ruptured. 

These  tests  serve  also  to  emphasize  the  fact  that  wrought  iron  is  an 
extremely  variable  material  when  forged  in  large  masses,  and  by  no  means  as 


From  Proc.  Inst.  Civ.  Eng.,  vol.  xciv.  p.  209. 


EFFECTS  OF  TEMPERATURE  ON  METALS. 


565 


TABLE    XXXVI. — ANDREWS'    TESTS    OX    WROUGHT-IROX    CAR-AXLES    AT    0' 

AXD    100°    F. 


COLD  TESTS  AT  0°  F. 

WARM  TESTS  AT  100°  F. 

Number  of 
Axle. 

Sum  of  all  Deflec 
tions  of  Axle 
in  Inches. 

Total  Number 
of  Blows  caus- 
ing Fracture. 

Number  of 
Axle. 

Sum  of  all  Deflec- 
tions of  Axle 
in  Inches. 

Total  Number 
of  Blows  caus- 
ing Fracture. 

44 

4.8 

8 

45                       133 

23 

46 

5.7 

8 

47 

11.9 

15 

48 

0.8 

2 

49 

199 

23 

50 

6.6 

8 

51                      14.4 

17 

52 

8.7 

11 

53                      217 

22 

54 

38.6 

44 

57                      71.1 

107 

55 

4.5 

6 

63                        9.1 

12 

56 

6.9 

10 

64                      31  4 

49 

58 

7.2 

9 

65 

32.1 

44 

59 

5.3 

7 

67 

40.9 

54 

60 

4.0 

6 

69 

17.9 

24 

61 

10.3 

14 

70 

16.4 

22 

62 

5.6 

8 

71 

47.5 

66 

66 

25.7 

33 

72 

43.8 

62 

68 

26.2 

32 

73 

37.5 

57 

77 

21.6 

29 

74 

25.9 

34 

78 

66.0 

84 

75 

12.1 

16 

79 

58.8 

76 

76 

17  2 

25 

80 

49.4 

64 

81 

17.8 

22 

83 

25.9 

34 

82 

23.4 

35 

84 

30.1 

42 

89 

24.5 

32 

87 

25.3 

32 

85 

34.4 

35 

88 

3.4 

5 

86 

10.6 

56 

90 

16.1 

20 

111 

34.6 

53 

91 

35.4 

48 

98 

52.8 

78 

92 

8.6 

12 

113 

30.4 

45 

93 

7.4 

10 

120 

23.1 

32 

94 

3.4 

5 

103 

34.5 

49 

95 

3.0 

5 

121 

25.9 

40 

96 

31.2 

43 

108 

41.1 

54 

Average 

18.2 

23.8 

Average 

27.7 

37.1 

uniform  as  mild  steel.  If  steel  axles  would  show  one  half  as  great  a  range 
in  results  as  is  here  revealed  for  wrought  iron,'  they  would  all  be  rejected 
without  any  hesitation. 


EFFECTS   ON   COPPER  AND  BRONZE. 

401.  Effects  on  Copper. — These  are  shown  in  Fig.  48G.  Both  the  elastic 
and  the  ultimate  strength  regularly  diminish  for  rising  temperatures,  while 
the  elongation  remains  nearly  constant  up  to  600°  F.  The  modulus  of 
elasticity  rises  to  a  maximum  at  the  boiling  temperature,  where  it  is  15  per 
cent  higher  than  at  a  freezing  temperature,  and  then  rapidly  declines.  The 
elastic-limit  strength  of  rolled  copper  may  be  said  to  diminish  at  the  rate  of 
5  per  cent  per  100°  F.  increase  in  temperature. 


566 


THE  MATERIALS  OF  CONSTRUCTION. 


402.  Effects  on  Bronze. — The  elastic  strength,  the  ultimate  strength, 
and  the  ductility  of  bronze  are  but  little  affected  by  rising  temperatures  up 
to  000°  P.,  the  reduction  in  strength  being  only  about  2  per  cent  per  100°  F. 


/00    200    <300      0       /00    200 

COPPER.  DELTA-METAL  (CAST). 

FIG.  486. — Tensile  Properties  of  Copper  and   Delta-metal   at  Various  Temperatures 
Centigrade.     (Berlin  Testing  Lab.,  1893.) 

within  this  limit,  as  shown  in  by  Fig.  487.     The  modulus  of  elasticity  rises 
some  20  per  cent  at  550°  F.,  and  then  rapidly  falls. 

80\ 


to/vc 


fLl/M/T 


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eo 

£0 

30 
20 

/O 

0 
0°C.  W0    200   <300     0      S00    200    <30O 

4%  MANGANESE  BRONZE.  DELTA-METAL  (ROLLED). 

FIG.  487. — Tensile  Properties  of  Manganese  Bronze  and  Delta-metal  (rolled)  at  Various 
Temperatures  Centigrade.     (Berlin  Testing  Lab.,  1893.) 


/woo 

/2T00 


BOOO 


EFFECTS  OF  TEMPERATURE  ON  METALS.  567 

403.  Effects  on  Delta-metal. — These  are  shown  in  Figs.  486  and  487  for 
cast  and  rolled  delta-metal  respectively.    The  ultimate  strength  falls  much 
more  rapidly  than  the  elastic  limit,  this  remaining  nearly  constant  up  to 
about  500°  F.     The  modulus  of  elasticity  falls  rapidly  after  passing  300°  F., 
but  the  ductility  increases  to  400°  F.  for  rolled,  and  to  550°  F.  with  the 
cast,  metal,  the  elongation  being  GO  per  cent  and  55  per  cent  respectively  at 
these  limits. 

404.  Conclusions. — In  general  it  may  be  said  that  copper  and  its  useful 
alloys  have  their  mechanical  properties  changed  but  little  for  the  variations 
of  temperature  ordinarily  occurring  in  the  use  of  these  materials  in  the  arts. 
See  Fig.  472  for  aluminum  bronze. 

For  very  low  temperatures  the  static  strength  of  iron  and  steel  increases 
somewhat,  but  both  elastic  limit  and  elongation,  or  ductility,  decrease,  so 
that  the  resistance  to  shock  is  considerably  reduced.  The  bad  effect  of  cold 
weather,  therefore,  is  shown  on  materials  subjected  to  heavy  blows,  like 
railroad  rails.  It  is  not  practicable  to  make  shock  tests  at  temperatures  lower 
than  that  found  out-of-doors  in  winter,  or  such  as  maybe  created  in  a  large 
refrigerating  warehouse.  Tests  at  extremely  low  temperatures,  therefore, 
such  as  shown  in  Fig.  477,  are  necessarily  limited  to  tension  tests  of  small 
specimens,  which  can  be  surrounded  by  a  cooling  apparatus. 

If  shock  tests  are  made  on  artificially  cooled  bars,  at  ordinary  tempera- 
tures, they  should  be  returned  to  the  refrigerator  after  each  blow,  or  at 
most  after  each  second  blow. 

The  curves  shown  in  Figs.  474  to  480  show  that  in  tension  tests  at 
ordinary  atmospheric  temperatures  no  note  need  be  made  of  the  particular 
temperature  of  the  test  bar.  It  is  very  different,  however,  with  impact 
tests  as  shown  for  wrought  iron  in  Fig.  485.  Here  even  these  atmospheric 
variations  are  important  and  the  temperature  should  always  be  noted.  In 
order  to  make  such  tests  comparable  they  should  be  made  at  about  the  same 
temperature,  and  60°  to  70°  F.  has  been  selected  as  the  ^standard.  Most 
kinds  of  test- specimens  could  be  brought  to  this  temperature  by  immersion 
in  water. 


CHAPTER  XXX. 

RESULTS  OF  TESTS  ON  CEMENTS,   CEMENT-MORTARS,   AND 

CONCRETES. 

TENSILE   AND   COMPRESSIVE   STRENGTH   OF   CEMENTS  AND   CEMENT  MORTARS. 

405.  Tensile  Strength  of  Natural  Cement. — As  shown  in  Art.  315,  Fig. 
337,  the  tensile  strength  of  cement  is  a  true  index  of  its  compressive  strength. 
It  was  also  stated  in  Art.  155  that  the  American  natural  cements  are,  as  a 
class,  of  a  superior  grade,  and  that  they  are  quite  sufficient  in  strength  for 
nearly  all  purposes  for  which  cement  is  required.  Occasional  failures  of  this 
class  of  cements  has,  however,  developed  an  undue  popular  prejudice  against 
them.  If  reasonable  precautions  were  exercised  in  testing  such  cements,  a 
great  deal  of  money  could  be  saved  with  no  prejudice  to  the  works  on  which 
it  might  be  used. 

Fig.   489  contains  the  average  results  of  many  thousands  of  tests  of 


O  S0  20  30  40  <f0 

FIG.  489. — Average  Results  of  Time  Tests  ou  Rosendale  cemeiit  Mortar.     (Boston  Main 

Drainage,  1885,  p.  121.) 

Rosendale-cement  mortars,  extending  over  the  several  years  of  the  construc- 
tion of.  the  Boston  Main  Drainage  works.  The  usual  mixture  for  natural- 
cement  mortar  is  1  C.  :  2  S.,  and  these  tests  give  for  this  mortar  an  average 
tensile  strength  of  180  Ibs.  per  square  inch  at  the  end  of  one  year.  In  Fig. 

568 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND  CONCRETES.     569 

490  this  mixture  had,  in  tests  made  during  the  construction  of  the  Cairo 
bridge  across  the  Ohio  River,  for  Milwaukee  cement,  160  Ibs.;  for  Utica 
cement,  145  Ibs. ;  and  for  Louisville,  140  Ibs.,  this  strength  having  been 
reached  in  each  instance  at  the  end  of  three  months. 


00 


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FIG.  490.— Time  Tests  on  Three  Standard  Natural-cement  Mortars.     (Joy,r.  Assoc.  Eng* 

Socs.,  vol.  ix.) 

Long-time  tests  of  Louisville-cement  mortar  mixed  the  same  as  is  usual 
with  Portland  cement,  1  C.  :  3  S.,  gave  at  one  year  an  average  tensile 
strength  of  230  Ibs.  per  square  inch,  as  shown  by  Fig.  491.  This  greater 
strength  is  probably  due  to  the  superior  methods  of  making  the  test  bri- 
quettes which  have  been  followed  in  this  department  for  many  years.  This 


570 


THE  MATERIALS  OF  CONSTRUCTION. 


figure  shows  the  average  strength  of  neat  Louisville  cement  to  be  500  Ibs. 
per  square  inch  in  one  year  when  mixed  on  the  "gig,"  a  kind  of  "  milk- 
shake "  apparatus,  described  in  Engineering  News,  vol.  xxv.  p.  3  (Jan.  3, 
1891). 


£00 


<300 


200 


/ 


y 


8 


O  /  2  & 

FIG.  491. — Average  Results  of  Time  Tests  on  Eight  Brands  of  Louisville  Cement, 
(St.  Louis  Water-works,  1896.) 

Similar  results  have  been  obtained  in  the  tests  of  natural  cement  made  in 
connection  with  the  building  of  the  new  Sault  Ste.  Marie  Canal  lock,  as 
shown  in  Fig.  492.  Here  one  brand  of  natural- cement  mortars  gave  at  one 


/    A/ 


y 


0  30  /00  tf0  200  £50          300          350 

FIG.  492.— Strength  of  One  Brand  of  Natural -cement  Mortar.      (Wheeler,  Rep.  Chf. 

Engrs.  1894,  p.  2352.) 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND  CONCRETES.     571 


year,  for  1  C.  :  1  S.,  500  Ibs. ;  1  C.  :  2  S.,  370  Ibs.;  and  1  C.  :  3  S.,  2GO  Ibs. 
tensile  strength.  An  average  of  five  brands  of  natural-cement  mortar, 
1  C.  :  1  S.  gave  at  three  months  380  Ibs.,  and  an  average  of  ten  brands  of 


0/23466 

FIG.  493.— Strength  of  Natural  Cement  Neat  and  1  C.  :  1  S.    (Wheeler,  Rep.  Chf.  Engrs. 

1895,  p.  2983.) 

natural  cement  neat  gave  at  six  months  410  Ibs.  tensile  strength,  as  shown 
in  Fig.  493. 

These  results  all  go  to  show  that  if   reasonable  care  be  exercised  in 


&  20  30  40  JO 

FIG.  494. — Average  Results  of  Time  Tests  on  Portland-cement  Mortar.     (Boston  Main 

Drainage,  1885.) 


572 


THE  MATERIALS  OF  CONSTRUCTION. 


inspecting  and  testing  the  cement,  the  standard  American  natural  cements 
are  abundantly  strong  for  a  large  proportion  of  the  work  requiring  the  use 
of  such  mute  rial. 

406.  Tensile  Strength  of  Portland  Cement. — The  average  results  of  tests 
on  Portland  cement  made  on  the  Boston  Main  Drainage  works  are  given  in 
Fig.  494.  Comparing  this  figure  with  Fig.  489,  we  may  say  that  4  to  1  of 
Portland  cement  is  fully  equal  to  2  to  1  mortar  of  natural  cement.  Similarly, 
from  these  same  figures  we  may  say  that  neat  Portland  cement  at  one  year 


200 

0  /  2 

FIG.  495. — Average  Tensile  Strength  of  Fifteen  Brands  of  Portland  Cement.     (St.  Louis 

Water  Dept.,  1896.) 

is  60  per  cent  stronger  than  neat  natural  cement,  and  that  standard  mortar 
composed  of  3  S.  :  1  C.  is  nearly  twice  as  strong  when  made  of  Portland 


0  /0  2O-  3O 

FIG.  496.— Results  of  Cement  Tests  made  at  the  Iowa  State  University. 

cement  as  when  made  of  natural  cement.     Similar  results  on  neat  cement 
are  shown  in  Fig.  490. 

In  Fig.  497  are  shown  Tetmajer's  average  relations  of  the  strength  of 
standard  natural-  and  Portland-cement  mortars  at  various  ages  up  to  one 
year,  as  percentages  of  the  strength  at  28  days.  From  this  it  appears  that 
natural-cement  mortar  at  one  year  is  twice  as  strong  as  it  is  at  28  days, 
while  Portland-cement  mortar  at  one  year  is  only  50  per  cent  stronger  than 
at  28  days.  Furthermore,  the  strength  of  the  natural  cement  is  still  increas- 
ing, while  that  of  the  Portland  cement  has  about  reached  its  maximum. 


TESTS  ON  CEMENTS,   CEMENT- MORTARS,  AND   CONCRETES.      573 

In  Fig.  498  are  given  the  average  results  of  tests  on  nine  brands  of 
Belgian  Portland  cement  and  on  twelve  brands  of  English  Portland,  both 
neat  and  1  C.  :  3  S.  It  would  seem  these  mortar  results  are  too  low  in 


200 


/OO          200          300        400 
FIG.  497.— Average   Relation  of   Strength  of   Cement-mortars  which   have   Hardened 
under  Water  for  periods  less  than  One  Year  to  the  Strength  of  Twenty-eight  Days. 
(Tetmajer's  Communications,  vol.  vi.  pp.  379-389.) 

comparison  with  the  results  on  the  neat  cement.  In  general  standard  mor- 
tar, 1C.  :  3  S.,  should  reach  one  half  the  tensile  strength  of  the  neat  cement 
at  the  end  of  a  year.  The  strength  of  Portland  cement,  both  neat  and  with 


FIG.  498. — Average  Results  of  Tension  Tests  on  Belgian  and  English  Portland  Cements. 
(Allison,  Trans.  Can.  Soc.  C.  E.t  vol.  ix,  1895,  p.  296.) 


574 


THE  MATERIALS  OF  CONSTRUCTION. 


sand,  continues  to  increase  for  many  years,  as  appears  from  Fig.  499.  Here 
the  strength  of  the  standard  mortar,  10.  :  3  S.,  was  65  per  cent  of  that  of 
the  neat  cement  at  one  year,  while  at  five  years  it  had  increased  to  75  per 
cent  of  the  strength  of  the  neat  cement  at  that  age.  Short-time  tests  on 


FIG.  499.— Long-time  Tests  of  American  and  Foreign  Portland  Cements.  Figures  give 
number  of  tests  averaged.  (Jour.  Assoc.  Eng.  Socs.,  vol.  xv.  p.  193,  and  Can.  Soc. 
C.  E.,  vol.  ix.) 

sand  mixtures  always  give  a  much  lower  ratio  of  strength  to  that  of  the  same 
cement  neat  than  long-time  tests.  It  will  be  observed,  also,  that  the  five- 
year  tests  in  Fig.  499  were  on  an  American  cement.  There  is  now  no  ques- 
tion as  to  the  superior  quality  of  many  brands  of  American  Portland  cement. 
This  is  also  shown  by  Fig.  500.  In  this  figure  the  ratio  of  the  strength  of 
the  mortar  is  so  low  as  to  lead  to  the  conclusion  that  no  special  pains  were 
taken  to  compact  the  briquettes.  The  strength  of  cement-mortar,  1  C.  : 
3  &.,  can  readily  be  increased  100  per  cent  by  mixing  somewhat  dry  and 
using  the  Bohme  hammer,  Fig.  352,  as  compared  to  the  strength  of  soft 
mortar  which  is  merely  pressed  into  the  moulds.  It  is  for  this  reason  that 
American  engineers  adhere  so  uniformly  to  the  neat  test,  the  strength  of 
neat  briquettes  not  being  so  much  affected  by  the  method  used  for  filling  the 
moulds. 

The  relative  effects  of  hardening  in  air  and  in  water  are  shown  in  Fig. 
502  for  one  brand  each  of  natural,  slag,  and  Portland  cement.  Evidently 
the  continued  presence  of  water  is  essential  to  the  greatest  strength  of  the 
Portland  cement,  while  the  natural  cement  reached  a  higher  strength  in  the 
air. 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.     575 

A  mixture  of  natural  and  Portland  cement  varies  in  strength  between 
that  of  the  true  ingredients,  strictly  in  proportion  to  the  percentage  of  each 
used,  as  shown  by  Fig.  503. 

A  mixture  of  1  S.  :  1  C.,  if  the  mixing  be  very  thorough,  has  about  the 
same  tensile  strength  as  the  same  cement  neat.  (See  Fig.  490.) 


W 


0          /W        200       300     400 

FIG.  500. — Average  Tensile  Strength  of  a  great  niauy  Samples  of  One  Brand  of  Ameri- 
can Portland  Cement  (1896).     (Robt.  W.  Hunt  &  Co.) 

407.  The  Modulus  of  Elasticity  of  Portland-cement  Mortars. — These  are 
shown  in  Fig.  504  for  two  brands  of  Portland  cement  and  one  brand  of  slag- 
cement.  The  modulus  increases  with  age,  as  would  be  expected,  but  it  is 
also  one  third  greater  for  standard  mortar,  1C.  :  3  S.,  than  it  is  for  the  neat 
cement,  which  could  hardly  have  been  predicted,  especially  when  determined 
from  a.  cross-bending  test.  The  modulus  is  very  much  lower  for  the  slag- 
cement  than  for  the  Portland  cement;  in  other  words,  the  slag-cement  is 
more  elastic,  or  resilient,  than  the  Portland.  This  is  an  important  quality 


576 


THE  MATERIALS  OF  CONSTRUCTION'. 


which  should  be  further  studied.  The  moduli  of  elasticity  in  compression 
of  neat-cement  mortars,  and  concretes  are  given  in  Art.  418,  Figs.  546, 
547,  and  548. 


408.  Strength  of  "  Sand-cement  "  Mortars. — Within  a  few  years  a  new 
product  has  been  introduced  (from  Denmark),  composed  of  Portland  cement 
reground  with  sand.  This  is  a  pure  dilution,  but  it  also  makes  available,  by 
regrinding,  the  coarser  particles  of  the  cement,  so  that  the  new  mixture  may 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.     577 

now  be  mixed  again  with  raw  sand,  the  same  as  the  pure  cement,  and  the 
result  is  a  considerable  cheapening  of  the  product  for  a  given  final  strength. 
Thus  if  three  parts  of  sand  be  ground  with  one  part  of  Portland  cement,  the 


600 


0          SOC          200         300      400 
FIG.  502.— Relative  Strength  of  Cement-mortars  when  Hardened  in  Air  and  in  Water. 
(Tetmajer's  Communications,  vol.  vi.) 

product  is  four  parts  of  "  sand-cement."     If  now  this  be  incorporated  with 
raw  sand  in  the  proportion  1:3,  we  shall  have  to  use  12  parts  of  raw  sand, 


578 


THE  MATERIALS  OF  CONSTRUCTION. 


making  in  all  15  parts  of  sand  to  1  of  cement.     The  formula  for  this  mortar 
would   be,   therefore,   1  :  3  :  12  =  1  C.  :  15   S.      The   tensile   strength  of 


.-. 


^ 


J® 


^  fM£fAnVI&)F  #A  /M\t/M\  £fMW/-(//£AT) 


FIG.  503.— Strength  of  Mixtures  of  Natural  and  Portland  Cement.     Average  of  tests 
from  one  week  to  one  year.     (Wheeler,  Rep.  Chf.  Engrs.  1894,  p.  2350.) 

various  such  mixtures,  at  ages  up  to  one  year,  are  given  in  Fig.  505,  in  com- 
parison with  the  strength  of  standard  mortar  1C.  :  3  S.  Thus  the  mixture 
1  :  2  :  G  —  1  0.  :  8  S.  gives  almost  as  great  strength  as  the  ordinary  1C.  :  3  S. 


FIG.  504. — Modulus  of  Elasticity  of  Portland-cement  Mortar  as  determined  by  Cross- 
beudiug  Tests.     (Inst.  Civ.  Engrs.,  vol.  cxi.  p.  109.) 

In  Fig.  506  both  the  tensile  and  the  compressive  strengths  of  sand-cement 
mixtures  are  given  from  1  C.  :  3  S.  to  1  :  3  :  8  =  1  C.  :  35  S.  In  Fig.  507 
these  same  results  are  plotted  to  the  argument  cement  -r-  total  sand  and 
cement. 


TESTS   ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.     579 

In  Fig.  508  the  tensile  and  the  compressive  strengths  are  given  for  a 
constant  total  ratio  of  sand  to  cement,  but  with  different  ratios  of  ground  to 
unground  sand. 

While  "  sand-cement  "  is  now  (1897)  manufactured  at  New  York  City, 
it  is  doubtful  if  it  ever  comes  to  be  used  very  much  in  America,  since  it 


FIG.  505. — Strength  of  Sand-cement  Mortar.  The  first  figure  denotes  parts  of  Port- 
land cement  ;  the  second,  parts  of  ground  sand;  the  third,  parts  of  ungrouud  sand. 
(Engr.  News,  April  10,  1896,  vol.  xxxv.  p.  254.) 

cannot  compete  in  price  with  our  excellent  natural  cements,  and  because 
Portland  cement  will  soon  be  made  here  in  sufficient  quantities  to  meet  the 
entire  home  demand,  and  at  prices  so  low  that  there  will  probably  be  little 
demand  for  this  kind  of  dilution. 

409.  Variation  of  Strength  of  Cement-mortar  with  Increasing  Propor- 
tions of  Sand. — This  law  is  largely  a  function  of  the  methods  employed  in 
mixing  the  mortar  and  in  compacting  it  in  the  moulds.  When  this  is 


580 


THE  MATERIALS  OF  CONSTRUCTION. 


PIG.  506.— Strength  of  "  Sand- cement"  Mortar  at  Twenty-eight  Days  for  Increasing 
Proportions  of  Free  Sand  when  mixed  with  "  Sand-cement  "  containing  1  C. :  3  S. 
(Uionindustrie-Zeitung,  January  6,  1896.) 


PIG.  507.— Strength  of  Sand-cement  Mortar  with  Varying  Proportions  of  Sand.    (Thon- 
indiLstrie-Zeilung ,  January  6,  1896.) 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.     581 


thoroughly  done,  the  strength  of  mortar  composed  of  1  C.  :  1  S.  will  be 
found  to  be  about  as  strong  as,  and  often  stronger  than,  that  of  the  neat 


400 


\ 


FIG.  508. — Variation  in  Strength  of  "  Sand-cement  "  Mortar  when  the  Total  Proportion 
of  Sand  is  constant,  but  a  Varying  Proportion  of  Ground  and  Unground.  (Thon- 
industrie-Zeitung,  January  6,  1896.) 


O  2  4  ff  & 

FIG.  509.— Showing  Reduction  of  Strength  of  Portland-cement  Mortar,   Six  Months 
Old,  with  Increasing  Proportions  of  Sand.    (Wheeler,  Rep.  C/>f.  Engrs.  1895,  p.  2982.) 

cement.     Thus  in  Fig.  517  the  1  :  1  mortar  was  stronger  than  the  neat 
Portland   cement.     The  standard  mixture  of  3  S.  :  1  C,  should   have,  in 


582 


THE  MATERIALS  OF  CONSTRUCTION. 


general,  about  one  half  the  strength  of  the  neat  cement  when  six  months 
old.     It  also  appears  from  Figs.  509  and  511  that  Portland-cement  mortar 


FIG.  510. — Showing  Reduction  in  Strength  of  Portland-cement  Mortars,  Six  Months  Old, 
with  Increasing  Proportions  of  Sand.     (Wheeler,  Rep.  Chf.  Engrs.  1895,  p.  2982.) 

of  4  S.  :  1  C.  has  the  same  strength  at  six  months  as  natural-cement  mortar 
of  2  S.  :  1  C.  of  same  age. 

Similar  relations  appear  in  Figs.  489,  494,  512,  513,  and  515. 


300 


ft  AT 


10 


SA/VrJ 


\ 


% 


.75 


50 


26 


0 


0  .020  #40  tfffl  tf$0 

FIG.  511.— Showing  Reduction  of  Strength  of  Natural-cement  Mortar,  Six  Months  Old, 
for  Increasing  Proportions  of  Sand.     (Wheeler,  Rep.  C7if.  Engrs.  1895,  p.  2982.) 

410.  Variation  of  the  Strength  of  Cement-mortars  with  a  Variation  in 
Size  of  the  Sand-grains. — Photographs  of  sand-grains,  natural  size,  obtained 


TESTS  ON  CEMENTS,   CEMENT- MORTARS,  AND   CONCRETES.      583 


by  the  use  of  graded  sieves,  are  shown  in  Figs.  518  to  523.     The  effect  of 
the  variation  in  size  of  the  sand-grains  was  discussed  and  results  shown  in 


"SiG.  512. — Strength  of  Cement-mortars,  at  Six  Months  Old,  for  Varying  Proportions  of 
Sand.     (Boston  Main  Drainage,  1885,  p.  122.) 


FIG.  513.— Tensile  Strength  of  Portland-cemeut  Mortar.     (Baker,  in  Masonry  Construc- 
tion, p.  90.) 

Art.  317.     It  there  appeared  that  sand  which  passes  a  No.  20  and  stops  oil 
a  No.  30  sieve  (20  and  30  meshes  per  linear  inch)  gave  the  strongest  mortars. 


584 


THE  MATERIALS  OF  CONSTRUCTION. 


It  is  shown  in  Fig.  516  that  mortar  from  this  grade  of  sand  is  from  25  to  50 
per  cent  stronger  than  mortar  made  from  sand  which  had  passed  a  No.  40 
and  stoDDed  on  a  No.  80  sieve. 


100  .30  .GO  .40  .20 

FIG.  514. —Ratio  of  Strength  of  Mortar  to  Strength  of  Neat  Cement  for  Different  Pro- 
portions  of  Sand.     (Rep.  N,  7.  State  Engr.  1894,  p.  336.) 


FIG.  515.— Tensile  Strength  of  Ilosendale  (Natural) 
Cement  Mortar.  (Baker,  in  Masonry  Construc- 
tion p.  90.) 


500 


400 


0 


FIG.  516.— Effect  of  Size  of  Sand- 
grains  on  the  Strength  of  Ce- 
ment-mortar, 3  S. :  1  C.  (Wheeler, 
Rep,  Chf.  Engrs.  1895,  p.  3013.) 


TESTS  ON  CEMENTS,   CEMENT-MORTARS,  AND   CO-NCRETES.     585 


M.  Feret*   has    for   many  years  made   a  study  of  the   effects   of  the 
"granulometric  "  composition  of  the  sand  on  the  various  qualities  of  tho 


FIG.  517.— Time  Tests  on  Three  Kinds  of  Portland  Mortar  with  Different  Sands.    (R.  R. 

Gazette,  1892.) 

resulting  mortars,  f     He   experimented   with  two   sands  of  the  following 
granulometric  compositions: 


Kind  of  Sand. 

Large  Grains, 
2.0  mm.  to  5.0  mm. 

Medium  Grains, 
0.5  mm.  to  2.0  mm. 

Fine  Grains, 
passing  0.5  mm. 

Coarse  (Gattemarre)  

52* 

48* 

o 

Fine  (Trouville)  ...         

\% 

24* 

75* 

The  granulometric  composition  was  found  by  sifting  through  thin  plates 
having  circular  holes  of  5  mm.,  2  mm.,  and  0.5  mm.  respectively,  with  the 

*  Chef  du  laboratoire  des  Fonts  et  Chaussees  a  Boulogne-sur-Mer,  France. 
f  See  his  papers  in  An.  d.  Fonts  et  Chaussces  for  Mar.  1890,  July  1892,  Aug.  1896, 
and  in  Baumateriaknkunde,  vol.  i,  No.  10. 


586 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG.  518. -Granite,  size  80-100. 


FIG.  519.— River-sand,  size  120-140. 


FIG.  520.— River-sand,  size  20-30. 


FIG   51   —River  s.m  ',  si/i>  VM 


FIG.  522— Granite,  size  12-10.  FIG.  523.— Rive r-san,l,  size  12-16. 

Photographs  of  Sand-grains.  Natural  Size.     (Cooper,   in  Jour.  Frank,   hist.,  vol. 

1896.) 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.     58? 

results  as  indicated  by  the  table  above.  When  all  possible  proportions  of 
coarse  and  fine  sand  had  been  tried  with  a  cement  ingredient  varying  from 
10  to  30  per  cent  of  the  total,  it  was  found  that  the  strongest  mortar  for  any 
given  percentage  of  cement  was  ahoays  found  for  a  weight  of  coarse  sand 
equal  to  twice  the  combined  weight  of  the  fine  sand  and  the  cement.  With 
this  condition  fixed,  the  strength  and  cost  of  all  mortar  mixtures  fulfilling 
this  condition  are  given  in  Fig.  524. 


4X>^t 


200 


/I 


kg 

1 


WAL 


LMi 


/ 


4 


CEI/fENT 


500 


g/7/2 

L/C/6/" 


uu 


£^ 
| 


70 
60 


^ 


4$ 


V 


v    /    £    3   4    5    6    7    & 

FIG.  524.— M.  Feret's  Maximum  Strength  Mixtures  in  which  the  Coarse  Sand  (S.)  is 
twice  the  Combined  Weight  of  the  Fine  Sand  (s.)  and  the  Cement  (c.).  (An.  d.  Fonts 
et  Ghaussees,  Aug.  1896,  p.  191.) 

411.  Relative  Economy  of  Coarse  and  Fine  Sand  in  Cement-mortars.— 

When  the  choice  lies  between  a  coarse  sand  and  a  fine  sand  exclusively  for 
use  in  cement-mortar  for  any  purpose,  the  preference  should  always  be  given 
to  the  coarse  sand,  even  though  its  cost  is  many  times  that  *of  the  fine  sand. 
Thus  M.  Feret  gives  as  a  generalization  from  his  years  of  experimentation 
on  this  subject*  a  table  from  which  Fig.  525  has  been  constructed.  Here 
we  have  as  a  common  argument  the  compressive  strength  of  the  mortar  mix- 
tures, at  the  age  of  three  months,  for  any  given  brand  of  Portland  cement. 
In  this  figure  we  have  for  the  two  sands  whose  granulometric  composition  is 
given  in  the  note  below  the  figure: 

1.  Weight  of  cement  to  use  with  one  cubic  yard  of  coarse  sand  to  produce 
a  mortar  of  any  given  strength. 

2.  The  same  for  fine  sand. 

3.  Weight  of  cement  to  use  to  produce  one  cubic  yard  of  mortar  of  any 
given  strength  when  coarse  sand  is  used. 


*  In  Les  Materiaux  de  Constructions  (Baumaterialenkiuide),  vol.  i.  p.  139. 


588  THE  MATERIALS  OF  CONSTRUCTION. 

21.00 


19.00 


FIG.  525.— Relative  Economy  of  Coarse  and  Fine  Sand  in  Portland-cement  Mortar 
1  C.  :  3  8.  after  Five  Months'  Immersion  in  Sea-water.  Coarse  sand  composed  of 
52#  2  mm.  to  5  mm.  diam.;  48#  0.5  mm.  to  2  mm.  diam.  Fine  sand,  25#  0.5  mm. 
to  2  mm.;  75*  less  than  0.5  mm.  rlinm.  (\\  ^ 


in 


TESTS  ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.     589 

4.  The  same  when  fine  sand  is  used. 

5.  Cost  per  cubic  yard  of  coarse-sand  mortars  of  any  given  strength. 

0.  The  same  for  line -sand  mortars  when  the  fine  sand  costs  only  fifteen 
per  cent  as  much  as  the  coarse  sand. 

7.  The  ratio  of  the  volume  of  coarse  sand  to  the  volume  of  the  mortar  of 
any  given  strength. 

8.  The  same  when  fine  sand  is  used. 

From  these  diagrams  the  following  remarkable  conclusions  may  be  drawn : 

A.  It  requires  about  twice  as  much  cement  mixed  with  a  given  quantity 
of  sand  to  produce  a  mortar  of  given  strength  when  fine  sand  is  used  as  it 
does  with  coarse  sand 

B.  The  weight  of  cemen^per^eulic  yard  of  mortar  of  a  given  strength  is 
about  twice  as  much  for  fine  sand  as  for  coarse  samL  with  the  ordinary  mix- 
tures. * 

C.  The  cost  per  cubic  yard  of  coarse-sand  mortar  of  a  given  strength 
(such  as  is  found  for  the  ordinary  ratio  1C.  :  3  S.)  is  only  about  seventy-five 
per  cent  of  the  cost  of  a  fine-sand  mortar  of  the  same  strength,  even  when  the 
coarse  sand  costs  six  and  two-thirds  times  as  much  as  the  fine  sand  (coarse 
sand  $1.30,  and  the  fine  sand  $0.20  per  cubic  yard). 

412.  Experiments  with  Sands  of  Artificial  Granulometric  Composition. 
— Very  coarse  or  gravelly  sands,  containing  pebbles  as  large  as  one-fourth 
inch  in  greatest  dimension,  may  be  introduced  into  a  mortar  used  in  making 
concrete,  or  in  rough  masonry,  with  great  economic  advantage.  M.  Feret 
has  studied  the  effects  of  the  use  of  such  sands,  mixed  in  various  proportions 
with  finer  grades,  and  some  of  his  results  are  given  in  Figs.  520  to  531  He 
used  fov  these  experiments  three  grades  of  sand,  namely: 


Grade  of  Sand. 

Passes  a  Perforated  Plate 
having  Holes  of  a  Diameter  of 

Is  Stopped  on  a  Plate  having 
Holes  of  a  Diameter  of 

Cocirsc  s<ind                 ....           .... 

5  mm    or  0  2  in 

2  mm   or  0  08  in 

Medium  s<ind       

2  mm.  or  0.08  in. 

0.5  mm.  or  0  02  in 

Fine  sand 

0.5  mm   or  0  02  in 

He  made  all  possible  mixtures  of  these  three  grades,  representing  each 
mixture  by  its  position  in  an  equilateral  triangle,  just  as  has  been  done  in 
the  case  of  the  bronzes  in  Fig.  7G.  Thus  in  Fig.  5*26  let  each  apex  of  the 
triangle  represent  100  per  cent  of  one  kind  of  sand,  and  on  perpendiculars 
drawn  from  these  points  to  the  opposite  sides  let  percentages  be  marked, 
reducing  to  zero  on  those  sides  as  shown  in  the  figure,  and  let  lines  be  drawn 
through  these  points  parallel  to  the  several  sides  as  shown.  Then  may  any 
particular  composition  of  sand,  made  up  of  any  given  proportions  of  the 
three  grades,  be  represented  by  the  position  of  a  point  which  shall  be  distant 
from  the  several  sides  by  amounts  equal  to  the  three  percentages,  as  indi- 
cated on  the  normals  to  these  sides.  This  follows  from  the  geometrical 


590 


THE  MATERIALS  OF  CONSTRUCTION. 


Fm.  526  —Showing  the  Method  of  Representing 
Proportionate  Mixtures  of  Three  Ingredients. 
G  =  coarse  sand,  0.2  in.  to  0.08  in.  in  diameter. 
M  =  medium  sand,  0.08  in.  to  0.02  in.  in  diameter. 
F  =  fine  sand  less  than  0.02  in.  in  diameter. 


FIG.  527. — Compressive  Resistance  of  Portland- 
cement  Mortars,  in  pounds  per  square  inch,  after 
nine  months  in  air  and  then  three  months  in 
sea-water.  Mortar  1  C.  :  3  S.  in  all  cases,  but 
the  composition  of  the  sand  varying  according 
to  position  in  the  triangle. 


FIG.  528.— Compressive  Resistance  of  Portland- 
cement  Mortars,  1  C.  :  3  S  ,  in  pounds  per  square 
inch,  after  one  year  in  sea-water.  Shaded 
part  indicates  mixtures  which  were  partially 
disintegrated. 


FIG.  529  — Compressive  Resistance  of  Portland 
cement  Mortars,  1  C.  :  3  S.,  in  pounds  per  square 
inch,  after  one  year  in  fresh  water. 


530.— Actual  Solid  Contents  (C.  +  S.)  of  Port-       FIG.   531.  —  The    Porosity    of     Portland-cement 
laud-cement  Mortars,  1  C. :  3  S.,  in  terms  of  the  Mortars,  1  C  :  3  S.,  as  indicated  by  the  percent- 

total  bulk  of  the  mortar.  age  of  water  absorbed  by  the  mortar  after  it 

had  hardened  and  dried. 

Samples  of  M.  Feret's  Diagrams  illustrating  Effects  of  Varying  the  Grauulometric 
Composition  of  the  Sand  used  in  making  Portland-cement  Mortars.  The  actual  sizes 
of  the  Sand-grains  of  the  Three  Ingredients  are  indicated  by  the  small  circles  at 


TESTS   ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.     591 

proposition  that  the  sum  of  the  three  normals  from  any  point  in  an  equi- 
lateral triangle  to  the  three  sides  is  equal  to  the  common  altitude  of  the 
triangle.  The  various  characteristics  of  such  mortars  may  now  be  repre- 
sented by  lines  drawn  upon  these  triangles,  which  shall  join  points  of  equal 
numerical  value  in  the  quality  under  consideration,  the  same  as  contour-lines 
on  a  map  join  points  of  equal  elevation  above  a  given  datum  plane. 

Thus  in  Fig.  527  the  cornpressive  resistance  in  pounds  per  square  inch 
is  indicated  for  all  possible  mixtures  of  these  three  grades  of  sand,  there 
being  in  all  cases  a  total  of  3  S.  to  1  C.  by  weight.  These  samples  were  all 
left  nine  months  in  the  air  and  then  three  months  in  sea-water.  From  this 
figure  we  conclude: 

A.  That  a  sand  composed  of  4  parts  of  very  coarse  sand  (0.08-0.20  in. 
diam.)  to  1  part  of  very  fine  sand  (less  than   0.02  hi.  diam.)  makes  the 
strongest  possible  mortar  of  1  C.  :  3  S. 

B.  That  the  strength  of  such  a  mortar  is  more  than  twice  as  much  as 
the   same   mortar    1    C.  :  3  S.    when   the   sand    is   composed   of   what   is 
commonly  regarded  as  "coarse  sand  "  (0.02-0.08  in.  diam.),  and  more  than 
three  times  as  strong  as  the  same  (1C.  :  3  S.)  mortar  when  the  sand  is  very 
fine  (less  than  0.02  in.  diam.). 

C.  That  a  mixture  of  two  grades  of  sand  of  widely  different  sizes  gives  a 
great  deal  stronger  mortar  for  given  proportions  of  sand  and  cement  than 
does  any  particular  size  when  used  by  itself. 

D.  It  follows  from  the  above  that  it  is  well  to  employ  as  coarse  a  sand 
as  the  work  will  admit  of,  even  to  the  finer  gravels  in  the  case  of  coarse 
masonry,  and  especially  with  the  concretes. 

E.  It  follows  also  that  in  the  case  of  concrete  mixtures  it  is  well  to  leave 
in  the  smaller  sizes  of  the  crushed  rock,  provided  the  very  fine  particles  be 
excluded.     This  has  been  found  to  be  the  case  in  actual  practice. 

F.  That  it  would  pay  to  use  very  coarse  sand  at  a  very  much  higher  price 
than  to  use  medium  or  fine  sand  at  a  low  price,  or  even  if  its  cost  be  nil. 

Very  similar  results  to  the  above  are  shown  in  Figs.  528  and  529,  from 
which  like  conclusions  may  be  drawn.  The  shaded  part  of  Fig.  528  indicates 
that  for  these  mixtures,  after  exposure  to  sea-water  for  one  year,  there  were 
some  signs  of  disintegration,  due  doubtless  to  the  greater  permeability  of 
these  mixtures.  (A  distinction  must  be  drawn  between  permeability  and 
porosity.  See  next  article.) 

413.  The  Porosity  of  Mortars  as  affected  by  the  Size  of  the  Sand-grains. 
—Figs.  530  and  531  indicate  the  relative  and  absolute  porosity  of  various 
sand  mixtures  as  affected  by  the  granulometric  composition  of  the  sand  used. 
Thus  Fig.  530  gives  the  actual  solid  contents,  per  unit  volume  of  mortar,  of 
the  cement  and  sand  combined  which  entered  into  the  composition.  Fig. 
531  gives  the  volume  of  water  absorbed,  per  unit  volume  of  the  dry  mortar, 
for  all  granulometric  compositions  of  the  sand.  In  both  cases  the  greatest 
porosity  is  found  with  the  finer  grades  of  sand,  and  the  least  for  a  mixture  of 
two  of  very  coarse  (gravelly)  sand  to  one  of  fine  sand. 


592 


THE  MATERIALS  OF  CONSTRUCTION. 


The  relative  permeability  cannot  be  assumed  to  vary  with  the  porosity, 
since  a  given  degree  of  porosity  with  coarse  sand  produces  a  much  more 
permeable  mortar  than  the  same  degree  of  porosity  with  fine  sand.  Hence 


in  Fig.  528  the  disintegrating  effect  of  the  sea- water  was  manifested  with  the 
coarse-sand  mixtures,  while  the  fine-sand  mixtures  did  not  reveal  any  such 
action,  although  its  porosity  was  much  greater. 


TESTS  ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.      593 

414.  The  Effect  of  Long  Storage  on  the  Strength  of  Cement. — The  effect 
of  long  storage  is  to  reduce  the  strength  of  the  cement  more  or  less,  whether 
this  be  Portland,  natural,  or  slag  cement.  The  injury,  however,  is  not  as 
great  as  is  commonly  supposed.  Thus  in  Fig.  532  we  have  both  tensile 
and  compressive  tests  on  standard  Portland-cement  mortar,  1  C.  :  3  S.,  for 
various  conditions  from  "fresh  burnt"  to  "very  lumpy."  The  loss  of 
tensile  strength  seems  to  be  less  than  the  loss  of  compressive  strength, 
though,  except  in  the  latter  case  for  the  "  very  lumpy,"  the  loss  is  not 
material. 

In  the  case  of  natural  cement  over  thirty  days  old  the  loss  of  tensile 
strength  is  considerable,  as  shown  in  Fig.  533.  Here,  however,  the  cement 
had  been  spread  out  and  exposed  to  the  air. 


300* 


FIG.  533.— Effect  of  Aeration  on  the  Strength  of  Natural-cement  Mortar.     (Wheeler, 
Rep.  Chf.  Engra.  1895,  p.  2962.) 

In  both  the  natural  and  in  the  slag  cements  there  is  free  lime,  which 
changes  to  the  inert  carbonate  of  lime  when  exposed  to  air  containing  carbon- 
dioxide  gas.  The  result  is  to  destroy  this  lime  ingredient.  In  other  cases, 
where  there  is  unslacked  free  lime,  a  long  aeration  allows  this  ingredient 
to  slack,  and  so  prevents  this  action  in  the  hardened  cement,  which  would 
swell  and  crack  it.  It  is  the  object  of  the  boiling  test  to  detect  the  presence 
of  auy  such  slow-slacking  free  lime  in  the  cement.  The  effects  of  long 
storage  of  slag-cement  containing  various  proportions  of  free  lime  on  both 
the  tensile  and  the  compressive  strength  are  shown  in  Fig.  534. 

415.  Effect  of  Regauging  after  Set  Begins.  —  It  is  commonly  understood 
that  cement  which  has  begun  to  set  is  more  or  less  weakened  by  regaining, 


594 


THE  MATERIALS  OF  CONSTRUCTION. 


and  that  such  cement  should  never  be  used  in  practice.  The  results  shown 
in  Figs.  535,  536,  and  537  reveal  to  what  extent  the  mortar  is  weakened. 
Thus  from  Fig.  535  it  may  be  seen  that  a  quick-setting  natural  cement 


mixed  neat  loses  ove^  25  per  cent  of  its  strength  at  six  months  from  having 
been  regauged  once  one  hour  after  wetting.  When  regauged  repeatedly  in 
3  or  5  hours  it  ^es  40  per  cent  of  its  normal  strength. 


TESTS  ON  CEMENTS,   CEMENT- MORTARS,  AND   CONCRETES.      595 

From  Fig.  53G  it  appears  that  a  Louisville-cement  mortar  1  C.  :  2  S. 
loses  -40  per  cent  of  its  normal  strength  at  three  months  by  standing  20 
minutes  after  Betting  before  moulding,  and  80  per  cent  of  its  normal 


300 


200 


I 


§ 

i^1 


I 
-I 


a 


1 


-i 


K 


FIG.  535,— Effect  of  Regauging  a  Quick-setting,  Neat  Natural-cement  Mortar,   Age 
Six  Months.     (Rep.  nJtf.  Engrs.  1895,  p.  2980.) 


,. 


•r- 


\ 


T/7O 


0  20  40          00 

FIG.  536.— Effect  on  tlie  Strength 
of  Louisville-cement  Mortar  of 
allowing  it  to  stand  a  given 
time  before  putting  into  the 
moulds.  (Jour.  West.  Soc. 
Engrs.,  vol.  i.  p.  82.) 


W£ffW3i'k 


FIG.  537.  — Strength  of  Itegauged  Neat  Port- 
land Cement  after  Six  Months'  Harden- 
ing in  Water.  Time  of  setting :  begins 
in  50  min.,  ends  in  3  hrs.  25  min. 
(Wheeler,  Eep.  Chf.  Engrs.  1895,  p. 
2979.) 


596 


THE  MATERIALS  OF  CONSTRUCTION. 


strength  by  standing  one  hour  before  moulding.     The  loss  of  strength  in  the 
1  C.  :  1  S.  mortar,  though  serious,  is  not  so  great.     This  is,  however,  a  very 


quick-setting  cement,  and  one  which  should  evidently  be  used  inside  of  20 
minutes  from  the  instant  of  wetting  it. 

The  loss  of  strength  from  regauging  one  or  more  times  a  neat  Portland- 
cement  mortar,  during  a  period  of  from  one  to  six  hours,  is  shown  in  Fig. 


TESTS  ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.      597 


537.  This  cement  completes  its  set  in  3  hours  25  minutes,  and  loses  18 
per  cent  from  being  regauged  once  in  five  hours  or  three  times  in  three 
hours.  Evidently  any  cement  will  be  greatly  weakened  if  used  after  it  has 
set. 

416.  Effect  of  Carbonic-acid  Gas  on  the  Hardening  of  Natural-  and  Slag- 
Cement  Mortars. — These  two  classes  of  cement  have  more  or  less  free  lime 
in  their  composition,  and  the  action  of  the  C02  on  this  is  to  change  it  into 
the  carbonate,  CaC03  (limestone),  which  would  naturally  add  to  the  strength 
of  the  mortar.  As  Portland  cement  does  not  contain  free  lime  to  any 
appreciable  extent,  it  would  not  be  similarly  affected.  In  Fig.  538  the 
effect  of  C02  on  a  natural-cement  mortar,  1C.  :  3  S.,  is  shown  to  be  very 
great  on  both  the  tensile  and  the  compressive  strength. 

From  Fig.  539  the  effect  on  slag-cement  is  not  so  great,  although  quite 
marked.  It  may  further  be  observed  from  this  dragram  that  while  harden- 
ing in  perfectly  dry  air  is  very  favorable  to  the  natural  cement,  it  is  very 
imfavorable  to  the  strength  of  the  slag-cement.  This  would  also  be  found 
to  be  the  case  with  Portland-cement  mortar.  Why  hardening  in  moist  air 
at  120°  F.  (50°  C.),  which  is  rich  in  CO, ,  should  be  so  very  unfavorable  to 
the  strength  of  natural  cement  does  not  appear. 


800 


80$ 


0 


FIG.  540. — Adhesive  Strength  of  Portland-cement  Mortar,  1  C.  :  1  S.,  Twenty-eight 
Days  Old,  to  Different  Substances,  and  the  Cohesive  Strength  of  the  Mortar  it- 
self. (Wheeler,  Rep.  Ohf.  Engrs.  1895,  p.  3019.) 

417.  The  Adhesive  Strength  of  Cement-mortars. — This  is  a  subject  of 
very  great  importance,  but  one  which  has  not  been  commonly  investigated. 
It  is  to  be  hoped  that  the  standard  methods  proposed  for  this  test  by  the 
French  Commission  will  lead  to  further  experiments  giving  comparable  re- 
sults. 


598 


THE  MATERIALS  OF  CONSTRUCTION. 


In  Fig.  540  the  adhesive  strength  of  Portland-cement  mortar,  1C.  :  1  S., 
is  given  for  various  substances.  Here  small  disks  of  the  substance,  1  inch 
square  and  £  inch  thick,  were  prepared  and  inserted  transversely  at  the  centre 
of  the  briquette-mould,  and  the  briquette  pulled  in  the  usual  manner,  with 
the  results  as  shown.  It  thus  appears  that,  whereas  the  cohesive  strength 
of  this  mortar  was  710  Ibs.,  its  adhesive  strength  varied  from  300  Ibs.  on 
sawn  brick  to  85  Ibs.  per  square  inch  on  sandstone  having  a  cleavage  surface. 

In  Fig.  541  it  is  shown  that  while  Portland-cement  mortar  will  adhere 


/SO 


L  O  UJ S  I//IL  £       C£M£A/T 

FIG.  541. — Adhesion  between  Louisville  (Natural)  and  Portland  Cement  Mortars.     (Jour. 

West.  Soc.  Engrs.,  vol.  i.  p.  82.) 

to  natural  (Louisville)  cement  mortar  when  both  are  fresh,  it  will  scarcely 
adhere  at  all  to  a  neat  natural-cement  surface  after  it  is  seven  days  old,  and 
it  adheres  very  poorly  to  a  1  C.  :  1  S.  natural-cement  mortar  a  week  old. 
The  neat  Portland  cement  did  adhere  to  the  neat  Louisville  cement  one 
week  old  with  a  force  of  85  Ibs.  per  square  inch,  but  the  Portland -cement 
sand-mixtures  would  not  adhere  to  it  with  any  appreciable  force. 

The  adhesion  of  natural  and  Portland  cement  mortars  to  sawn  limestone,. 
as  compared  with  their  cohesive  strength,  is  shown  by  the  diagrams  in  Fig 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.       599 


/  2 

PORTLAND  CEMENT. 

FIG.  542. — Relation  between  the  Adhesive  Strength  at  Twenty-eight  Days  of  Cement- 
mortars  to  Sawn  Limestone  and  the  Cohesive  Strength  of  the  Mortars  themselves, 
(Wheeler,  Rep.  Chf.  Engrs.  1895.  pp.  3020-21.) 


i 


0/234 

FIG.  543. — Adhesive  Strength  of  Mortar  to  Brick  Surfaces.     (Baker's  Maxonry,  p.  94.) 


600 


THE  MATERIALS  OF  CONSTRUCTION* 


tot 


60L 
60C 
406 
300 
200 
/OO 


ADh 


m/nAaFtW* 


SLU 


Fig.  544«.— Showing  the  Variation  in 
the  Modulus  of  Elasticity  of  Port- 
land-cement Mortar  in  Compres- 
sion, at  the  age  of  Three  Months 
when  tested  in  Cylinders  10  in.  in 
Diameter  and  40  in.  long.  (Prof, 
C.  Bach  in  Zeite  Ver.  Deuts.  Ing., 
Nov.  28,  1896. 


/  2  3 

SAND  70   /  OF  CEM 

FIG.  544.— Relation  between  the  Cohesive  Strength  of  Cement-mortar  and  its  Adhesive 
Strength  to  Brick  Surfaces  when  Two  Bricks  are  cemented  together  in  cruciform 
shape  and  pulled  normally.  The  results  are  the  means  of  three  mouths'  and  siz 
months'  tests  on  both  die  and  stock  brick.  (Wheeler,  Eep.  Chf.  Engra*  1895,  p. 


FIG.  545.— Adhesion  of  Plain  1-iuch  Round  Bolts  in  Neat  Portland-cement  Mortar,  Age 
One  Month.  Adhesion  given  in  pounds  per  square  inch  of  surface  of  bolt  em- 
bedded. (Wheeler,  Hep.  Ghf.  Engrs.  1895,  p.  2941.) 


TESTS  OX  CEMENTS,  CEMENT- MORTARS.  AND  CONCRETES*       601 

54^.     In  general  we  may  say  the  adhesive  strength  here  shown  is  less  than 
one  half  the  cohesive  strength. 

The  adhesive  force  of  ordinary  cement-mortars  to  brick  surfaces  is  very 
small,  Ufc  shown  by  Figs.  543  and  544.  A  strength  of  25  Ibs.  per  square  inch 
seems  to  be  about  all  that  can  be  ordinarily  counted  on  This  low  adhesive 
strength  may  be  partly  clue  to  the  fact  that  the  bricks  are  covered  with  a 
coating  of  disturbed  and  loose  particles.  A  clean,  fresh  fracture  would 
probably  show  a  much  greater  cohesion. 


-,ii 


c    .^ 


Wt 


«V-    C      >-n 


d-  E   t> 


3.  B 

51 
il 

pi    CD 


0      s 

\  __  .• 


NX< 
\ 


Oo 


sfc 


^ 


The  adhesion  of  cement-mortar  to  anchor-bolts  embedded  in  stone  is  very 
great,  as  shown  by  Fig.  545.  These  tests  agree  well  with  experiments  made 
by  the  author.  The  ultimate  strength  at  three  or  six  months  would  be 


602 


THE  MATERIALS  OF  CONSTRUCTION. 


nearly  twice  as  much  as  shown  in  the  diagrams,  which  are  for  an  age  of  fou: 
weeks.  The  same  department  obtained  about  twice  the  adhesive  strengtl 
shown  in  Fig.  545  by  using  limestone  screenings,  passing  a  f -inch-mesh  sieve 


K 

r 


s 


K 


X 


CD 


/v 


p 


(£>*• 


\ 


X 


\ 


using  2  S.  to  1  C.  Hence  the  ultimate  adhesive  strength  of  a  good  Portland 
cement  with  limestone  screenings,  1  0.  :  2  S.,  to  plain  iron  or  steel  bolts, 
may  be  taken  at  about  1000  Ibs.  per  square  inch.  To  develop  a  working 
strength  on  anchor-bolts,  therefore,  of  20,000  Ibs.  per  square  inch  would  re- 


TESTS   ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.      603 

quire  a  depth  of  adhesive  surface  equal  to  20  diameters  of  the  bolt.  To  pro- 
vide a  sufficient  factor  of  safety  a  depth  of  30  or  40  diameters  should  be 
used. 

418.   Compressive  Strength  and  Elasticity  of  Cement  and  Concrete. — In 
Fig.  540  are  shown  the  results  of  Prof.  Bach's  tests  on  concrete  columns  10 


inches  in  diameter  and  40  inches  long.  The  deformations  of  these  blocks 
were  obtained  with  the  apparatus  shown  in  Fig.  261,  p.  356.  These  blocks 
were  composed  of  Portland  cement,  sand,  and  gravel,  and  they  exhibit  two 
remarkable  characteristics.  They  do  not  give  the  reverse-curved  stress- 


604 


THE  MATERIALS  OF  CONSTRUCTION. 


diagrams  commonly  obtained  with  concrete  and  stone  blocks  and  shown  in 
Figs.  547  and  548,  and  they  also  give  very  high  moduli  of  elasticity.     The 


FIG.  549.— Showing  Method  of  Failure  of  Cement  Cubes.     (Wat.  Ars.  Rep.  1884.) 
author  has  not  found  any  other  tests  giving  these  two  characteristics  in  so 
marked  a  degree.     The  mixtures  were  doubtless  very  carefully  made. 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.      605 

Figs.  547  and  548  are  compiled  from  Gilmore's  Limes,  Mortars,  and 
Cements.  Here  the  modulus  of  elasticity  is  only  from  one  third  to  one  half 
that  obtained  by  Bach,*  and  there  is  always  a  large  permanent  set  under  the 
earliest,  or  smallest,  loads.  Probably  this  is  due  to  imperfect  mixing  or  to 
poor  compacting  in  the  moulds,  or  to  both.  Gilmore's  tests  were  made  on 
the  Emery  machine  at  the  Watertown  Arsenal.  The  manner  in  which  these 
cubes  fail  under  compression  is  shown  in  Fig.  549.  Bach's  moduli  of 
elasticity  on  cement-mortar  columns  are  given  in  Fig.  544#,  p.  600. 

419.  Strength  and  Economy  of  Cement-mortar  and  Concrete. — There  is 
no  very  uniform  practice  in  America  in  the  number  of  parts  of  sand  to  one 
of  cement  to  be  used  in  mortars.  In  general  natural  cement  is  used  with 
one  or  two  parts  of  sand,  while  Portland  cement  is  commonly  used  with  three 
parts  of  sand  to  one  of  the  cement  by  measure.  Whether  the  cement  is  to 
be  measured  in  the  original  packages  or  in  the  loose  condition  it  assumes 
when  turned  out  is  a  matter  of  great  significance,  but  no  uniform  practice 
is  followed,  and  usually  the  specification  is  defective  in  not  defining  which 
method  is  to  be  employed.  The  amount  of  sand  which  may  be  used*  with  a 
given  cement  depends  on  the  percentage  of  voids  in  the  sand,  and  on  the 
fineness  of  the  cement.  If  the  sand-grains  are  graded  in  size,  the  voids  are  a- 
smaller  proportion;  and  if  the  cement  is  all  finely  ground,  it  is  all  active. 
Such  parts  of  the  cement  as  will  not  pass  a  No.  120  sieve  (14,400  meshes  per 
lineal  inch)  has  no  value  as  a  cement  and  acts  as  so  much  sand. 

In  Fig.  550  are  shown  the  results  of  an  excellent  series  ,of  tests  made  by 
Mr.  E.  S.  Wheeler,  M.  Am.  Soc.  C.  E.,  in  connection  with  the  building  of 
the  St.  Mary's  Falls  Canal  lock.  Here  the  natural-cement  mortars  all  give 
the  greatest  strength  for  a  given  cost,  the  price  of  the  natural  cement  being 
43  per  cent  of  that  of  the  Portland  cement,  delivered  on  the  works.  The 
most  economical  natural-cement  mortar  is  that  of  1  C.  :  2  S.  or  1  C.  :  3  S. 
Probably  1  C.  :  2|  S.  is  the  best  mixture  for  natural  cement.  With  the 
Portland  cement  the  mixtures  1C.  :  2  S.,  1  C.  :  3  S.,  and  1C.  :  4  S.  were 
all  about  equally  strong  for  a  given  cost,  or,  what  is  the  san)e  thing,  these 
mixtures  are  about  equally  expensive  for  a  given  strength. 

Evidently  an  ideal  concrete  is  one  in  which  all  voids  are  filled,  all  sand- 
grains  are  coated  with  cement,  and  all  pebbles,  gravel,  or  broken  stones  are 
coated  with  mortar,  with  no  excess  of  cement  or  mortar.  This  requires  that 
enough  cement  must  be  used  to  fill  the  voids  in  the  sand  (plus  some  excess 
to  cover  imperfect  mixing),  and  enough  mortar  used  to  fill  the  voids  in  the 
stone  or  gravel  (plus  an  excess  as  before).  In  the  Report  of  the  Chief  of 
Engineers  of  the  U.  S.  Army  for  1895, f  pp.  2924  to  2931,  will  be  found 

*  To  read  the  modulus  of  elasticity  from  any  of  the  curves  in  Figs.  546,  547,  or  548, 
find  the  change  of  load  per  square  inch  for  which  the  proportionate  compression  is 
0.001,  and  multiply  such  change  in  load  by  1000,  using  the  straight  portion. of  the 
diagrams  for  such  readings. 

f  Under  the  direction  of  Mr.  E.  S.  Wheeler,  U.  S.  Ass't  Eng'r  in  charge  of  the  con- 
struction of  locks  on  the  St.  Mary's  Falls  Canal. 


606 


THIS  MATERIALS  OF  CONSTRUCTION. 


the  records  of  the  most  complete  series  of  tests  of  the  cross-breaking  strength 
of  concrete  beams  ever  made.  These  beams  were  all  10  inches  square,  and 
were  broken  on  a  span  of  4  feet.  There  are  here  recorded  the  results  of 
tests  on  over  one  hundred  such  beams,  forty  of  which  were  again  broken  on 
a  span  of  20  inches.  The  first  breaks  were  at  one  year  old,  and  the  second 
at  22  months.  All  kinds  of  mixtures  and  conditions  were  used  in  the  making 
of  the  beams,  and  they  were  covered  by  moist  earth  during  the  entire  harden- 
ing period,  or  until  broken.*  In  all  these  tests  the  proportions  by  both 

60 


800 

6.00 
400 


K 


PART, 


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FIG.  550.— Relation  between  Strength  and  Cost  of  Natural-  and  Portland-cement 
Mortars.  Prices  :  Nat.  cem.  =  $1.30  per  bbl. ;  Port.  cem.  =  $3.00  per  bbl. ;  sand  = 
$1.00  per  cu.  yd.  (Wheeler,  Rep.  Chf.  Engrs.  1893,  vol.  iv.  p.  3022.) 

weight  and  by  volume  are  recorded,  and  the  cost  of  each  part,  and  many 
other  pertinent  facts.  A  few  of  these  results,  which  were  of  the  nature  of  a 
series,  are  plotted  in  Figures  551  to  554,  and  the  full  record  of  the  tests  is 
given  in  Table  XXXVII. 

In  Fig.  551  the  cost  per  cubic  yard  and  the  cross-breaking  strength  in 
pounds  per  square  inch  are  given  for  various  mixtures  of  Portland-cement 
concrete.  From  this  diagram  the  most  economical  mixture  does  not  appear. 
Evidently  the  greatest  economy  corresponds  to  the  greatest  ratio  of  strength 
to  cost,  or,  what  is  the  same  thing,  the  minimum  ratio  of  cost  to  strength. 
This  may  be  shown  by  plotting  one  of  these  ratios  to  the  number  of  parts  of 
sand  and  stone  to  one  of  cement.  This  is  done  in  Fig.  552.  From  this  it 
appears  that  the  most  economical  mixture  of  Portland-cement  concrete  (the 

*  The  series  was  not  completed  at  the  time  of  the  1895  report,  and  the  1896  report 
•will  contain  further  results. 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND  CONCRETES.       607 

prices  being  $3.00  per  barrel  for  cement,  50  cents  per  cubic  yard  of  sand, 
and  $1.00  per  cubic  yard  of  stone  or  gravel)  is  1  C.  :  3  S.  :  7£  broken  stone 
or  gravel,  all  by  volume.*  The  cross-breaking  modulus  of  rupture  of  this 


6 


) 


6V. 


/S 


#00 


FIG.  551.  —  Relation  between  Cost  and  Strength  of  Portland-concrete  Beams  Nineteen 
Months  Old.  Each  result  is  the  mean  of  two  tests  on  beams  10  in.  square.  Por- 
tions of  sand  and  stone  are  given  to  1  of  cement.  Cement  $3  00  per  bbl.;  sand 
$0.50  and  stone  $1,00  per  cu.  yd.  (Wheeler,  Rep.  Chf.  Engrs.  1895.) 

mixture  (the  value  of/  in  the  formula  M—  \fbltf,  where  M=  bending 
moment,  b  =  breadth,  and  h  =  depth  of  the  beam)  is  about  500  Ibs.  per 
square  inch  at  the  age  of  19  months.  A  mixture  of  1  C.  :  2  S.  :  5  stone  is 


*  The  cement  is  here  taken  as  packed  in  the  barrel,  and  the  sand  and  stone  are  taken 
loose.     The  dry  weights  of  each  are  also  given  in  the  original  tables. 


608 


THE  MATERIALS  OF  CONSTRUCTION. 


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TESTS  ON  CEMENTS,    CEMENT-MORTARS,   AND   CONCRETES.     609 


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610 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE  XXXVIK7. — COMPOSITION,  COST,  AXD  STRENGTH  OF  NATURAL-CEMENT 
CONCRETE    BEAMS    10    INCHES    SQUARE  (ST.  MARY'S    CANAL    LOCKS). 


Proportionate 
Amounts  for 
1  Cubic  Foot,  of 
Packed  Cement 
(75  Ibs.  Natural, 

Proportionate 
Amounts  for 
1  bbl.  Packed 
Cement  (280  Ibs. 
Natural.  380  Ibs. 

Cost 
pel- 
Cubic 
Yard. 

Transverse 
Strength  on 
4-foot  Span. 

Trans- 
verse 
Strength 
on  20-inch 
Span. 

104  Ibs.  Portland). 

Portland). 

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6.7    15.6 

yr 

136 

124 

Sandstone  £"  to  3"  in  size 

1.78 

4.18 

6.7    15.  C 

lyr 

148 

150 

Limestone,  (D.  1.),   f"  in  to 

3"  in  size 

1.78 

4.18 

6.7 

15.6 

9.1    i         '4.14 

1  yr 

140 

222 

Limestone  (K.I.),"shavings" 

being  flat  spalls 

2.16 

4.18 

8  1     15  fi 

9.9 

4.00 

1  vr 

140 

94 

Sandstone 

2J6 

4.18 

8.1   Il5.6 

1  yr 

141 

96 

Limestone  (D.  I.) 

2.16 

4.18 

8.1   115.0 

lyr 

139 

202 

35m 

337    Limestone  (K.I.),"shavings" 

or  flat  spalls 

2  30 

8  23 

2.838  44 

8.573.07 

10.6 

31.53.62 

•2.25 

1  yr 

150 

120 

22m 

187 

Gravel  \"  to  1"  in  size 

6.86 

2.71  7.18 

8.47  2.56 

10.1 

26.9  3.89 

2.45 

1  yr 

151 

74 

22m 

197 

i.                         U 

2.25 

10  17 

2  729.928.4-23.80 

10.2 

37.1  3.  8912.10 

1  yr    146 

110 

22m 

197 

6.86 

2.71  6.868  47,2.56 

10.1 

25.63.96 

2.55 

1  yr    146 

1-23 

22m 

253 

Sandstone,  f  "  to  3"  in  size 

2  25 

10.17 

2.729  12 

8.4213.80 

10.2 

34.1 

4  24 

2.30 

1  yr    131 

74 

22m 

151 

"               *» 

1.87 

5  33 

2.425.55 

-.0020.0 

9.1 

20.84.24 

2.80 

lyr    138 

181 

18m 

276 

"       quite  dry 

1  87 

5.33 

2.  42  5.  C  5 

".0020  0 

9.1 

20.84.24 

2.80 

lyr    139 

214 

18m 

246 

"               "               " 

1.87 

5  33 

2.42  5.55 

".0020.0 

9  1 

20  84.24  2.80 

lyr    138 

175 

18m 

287 

It                                 1(                                U 

1.50 

5.38 

2.075.42 

5.6 

20.2 

7.7 

20.34.88 

2.85 

1  yri   140 

194 

18m 

261     1 

1.50 
1.50 

5.38 
5.38 
4.15 

2.075.42 
2.075.42 
.80  4.60 

5.6 
5.6 
4.2 

20  2 
20.2 
17.8 

(>  7 

20.34.88 
20  3  4  88 
17.25.50 

2.85 
2  85 
3.17 

1  yr  136 
1  yr 

1  yr|   140 

210 
275 

18m 
8m 

256 
312 

1  Sandstone,  f"  to  3"  in  size, 
"     somewhat  dry 

l!l2 

4.15 

1.804.60 

4.2 

17.8 

6.7 

17.2 

5  50 

3.17 

1  yr(  137 

306 

8m 

422 

J 

0.75 

3.05 

1.463.17 

2.8 

11.4 

5  5 

11.9 

6  64 

4.05 

19m 

303 

1  Sandstone,  |x/  to  3"  in  size, 

0.75 

3.05 

1.463.17 

2.8 

11.4 

5.5 

11.6 

6.64 

4.05 

19m 

477 

)      somewhat  wet 

1.50 

4.06 

2.09 

4.37 

5.6 

15  2 

7.8    16  4 

4.85 

3.20 

19m 

313 

1 

1.50 

4.06 

2  094.37 

5.6 

15  2 

7.8  ,16.4 

4.85 

3.20 

19m] 

351 

2.25 

5.902.856.00 

8.4 

22.1 

10  7    22  5 

3.65 

2.70 

19m 

206 

!  Sandstone,  f"  to  3"  in  size, 

2  25 

5.902  856.00 

8.4 

22  1 

10  7    22.5 

3  65 

2.70    9m 

274 

f     somewhat  dry 

3  'ob 

7.403.557.60 

11.227.7 

13.3 

28.5 

3.10 

2.40 

19m 

3.00 

7.403.557.60 

11  227  7 

13.3 

28.5 

3  10 

2  40 

19m 

185 

J 

2  25 

6.562.856  30 

8.4 

24.5 

10  7 

23  6 

3.63 

2  70 

llm 

237 

(Limestone      (D.      I.),     no 

2  .  25 

6.56  2.  85:6.  3( 

8.4 

24  5.    10.7 

23.6 

3.63 

2.70 

llm 

229 

\      screenings 

2  28 
2  28 

6.56 
6.56 

2  85 
2  85 

6.56 
6  50 

8.5 
8  .  5 

24.5 
24.5 

10  7 
10.7 

•24  fi 
24.6 

3.63 

3.63 

•2  60 
•2  60 

llm 
llm 

177 

216 

)  Limestone  (D,  I.),   10   pts. 
V     screenings    to    100    pts. 
|      stone 

2  2; 
2-2- 
1  2f 
1.28 

6.56 
6.5C. 
7.30  2  02 
7.30  ->.02 

6  73 

6  73 
6.8'. 
ti  8- 

8  4 
8  4 
4.H3 
1  83 

24.5 
24  .  r 
27  3 

7  .  56 
7  .  56 

25  2 

25.6 
25  C 

5  00 
5.00 

2.50 
2.50 
2.55 
2  .  5f 

llm 
lln 
lln 
lln 

216 
173 
230 
225 

]  Limestone   (D.  I.),  17  pts. 
}-     screenings    to    100    pts. 
stone 

2  2? 
2.2S 

6  5C 
6.56 

2  89 

2.89 

6.8S 
6.8; 

8.5 
8.5 

24  5 
24.  P 

10  85 
10.85 

25.fi 
25  C 

3.57 
3.57 

2  5C 
2.5C 

lln 

187 
216 

J 

)  Limestone  (D.  I  ),  50  pts. 
V     screenings    to    100    pts. 
)     stone 

1.1 

6  5( 
6  5( 

2  8r 

2.82 

7  U 
7.1: 

J8  5 
J8.5 

24.  f 

24.  f 

10  7 
10  7 

26  7 
26.7 

3  6;- 
3  6: 

2.3J 

2  3J 

llrr 
lln 

i 

101 
144 

)  Limestone  (D.  I.),   100  pts. 
V     screenings    to    100    pts» 
)      stone 

2  2£ 

6.562  Sf 

6  8- 

18  5 

24  f 

10  7 

25  6 

36: 

2.5( 

llrr 

i 

130 

Limestone   (D     I.),    screen- 

ings only 

TESTS  ON  CEMENTS,   CEMENT-MORTARS,  AND^  CONCRETES.      611 

25  per  cent  stronger  but  12  per  cent  more  expensive  for  a  given  strength, 
while  a  mixture  of  1  0.  :  4  S.  :  10  stone  is  12  per  cent  weaker  and  about  10 
per  cent  more  expensive  for  a  given  strength,  than  the  mixture  1C.  :  3  S. 

:  7-J  stone,  all  by  volume. 


I 

^ 


/frSW/f, 


aO 


w 


FIG.  552. — Economy  in  Portland-cement-concrete  Mixtures  as  shown  by  Tests  of  Con- 
crete Beams.  Each  result  the  mean  of  two  tests  on  beams  10  in.  square.  Cement 
$3.00  per  bbl.;  sand  $0.50  and  stone  $1.00  per  cu.  yd.  ( Wheeler,  Rep.  Chf.  Engrs. 
1895,  p.  2926.) 

In  Fig.  553  are  shown  the  results  of  tests  on  Portland-cement  concrete 
beams  where  the  mortar  was  always  the  same  (1  C.  :  3  S.),  while  the  stone 
ingredient  varied.  Results  are  here  shown  for  an  age  of  o:ie  year  and  also 
of  22  months.  It  is  very  noticeable  that  the  strength  at  22  months  is  much 
greater  (about  60  per  cent  greater)  than  at  12  months.  This  apparently 
great  increase  in  strength  may  be  partly  due  to  the  shorter  length  of  beam, 
this  being  but  20  inches  between  supports,  as  compared  with  48  inches  for 
the  12 -month  tests. 

Here  again  the  maximum  economy  is  found  for  the  mixture  1C.  :  3  S. 

:  7i  stone,  as  shown  by  the  curve  marked  "Katio  of  cost  to  strength."    For 
this  mixture  the  voids  are  just  filled,  while  with  a  less  amount  of  stone  there 

is  an  excess  of  mortar,  and  with  a  greater  proportion  the  voids  are  not  filled. 


612 


THE  MATERIALS  OF  CONSTRUCTION, 


In  the  case  of  natural-cement  mortar,  the  cost  of  the  cement  being  now  $1.30 
per  barrel  instead  of  $3.00,  the  most  economical  mixture  is  about  1  C.  :  1-J- 
S.  :  4  stone,  as  shown  by  Fig.  554.  The  data  on  these  mixtures  were  as 
follows : 


Mixture. 

Cost  per  Cubic  Yard  in 
Dollars. 

Cross-breaking  Modulus  in 
Pounds  per  Square  Inch. 

1  C 

•    4  S 

•  3  Stone     

4.05 

420 

1  C 

.  ii  g 

•  4  8  tone          

3.20 

332 

1  r 

•  *>i  S 

•  5  9  Stone 

2.70 

240 

1  C 

•  »*  o. 
•  3    S 

2.40 

186 

The  effect  of  making  a  portion  (13  per  cent)  of  the  broken  stone  consist 
of  screenings,  such  as  are  formed  when  a  rock-crusher  is  employed,  is  shown 
in  Fig.  553.  This  is  very  marked  where  there  is  a  deficiency  of  mortar. 


WO 


£00 


M 

6  <S  SO 

FIG.  553.— Strength  of  Portland-cement-concrete  Beams.  Effect  of  Varying  Propor- 
tions of  Stone  to  1  of  Cement,  always  using  3  Sand  to  1  Cement.  Each  result  is  the 
mean  of  two  tests  on  beams  10  in.  square.  Stone  passed  1-in.  screen  and  stopped  on 
f-inch.  Cement  $3.00  per  bbl.;  sand  $0.50  and  stone  $1.00  per  cu.  yd.  (Wheeler, 
Rep.  Chf.  Engrs.  1895,  p.  2924.) 

Thus  with  the  mixture  10.  :  3  S.  :  11.4  stone  the  strength  was  increased 
about  25  per  cent  by  making  the  broken  stone  consist  of  13  per  cent  screen- 
ings. Where  the  mortar  is  sufficient  to  fill  the  voids  of  the  stone  or  gravel 
the  fine  screenings  would  weaken  the  concrete,  as  they  would  be  equivalent 
to  so  much  additional  sand. 

420.  Filtration  through  Concrete. — In  Fig.  555  are  given  results  of  fil- 
tration experiments  on  Portland-cement  concrete  of  different  mixtures.  The 
most  remarkable  feature  of  this  diagram  consists  in  the  evidence  it  offers  of 
the  rapid  closing  of  the  openings  in  the  mass.  At  the  end  of  18  days  the 


TESTS  ON  CEMENTS,  CEMENT- MORTARS,  AND   CONCRETES.      613 

filtration  had  practically  ceased  in  all  the  mixtures,  although  the  concrete 
was  three  months  old  when  the  experiments  began.  Whether  this  rapid 
diminution  in  the  rate  of  nitration  is  due  to  the  progressive  crystallization 
of  the  cement  as  a  result  of  the  flow  of  water  through  it  or.  from  some  other 
cause  does  not  appear.  It  is  commonly  accepted  that  the  disintegration  of 
Portland-cement  concrete  is  primarily  due  to  its  permeability,  and  hence 
nitration  tests  are  made  to  determine  this  property.  As  all  of  the  mixtures 
shown  in  Fig.  555  become  practically  impervious  to  water  in  a  few  days,  they 
should  be  considered  as  entirely  satisfactory  on  this  score. 


S  JO 

FIG.  554.— Economy  in  Natural-cement-concrete  Mixtures  as  shown  by  Tests  of  Con- 
crete Beams.  Each  result  is  the  mean  of  two  tests  on  beams  10  in.  square  and 
nineteen  months  old.  (Wheeler,  Rep.  Chf.  Engrs.  1895,  p.  2929.) 

421.  The  Effects  of  Freezing  on  Cement-mortars  and  Concretes. — The 

disintegration  of  cement-mortars  and  concretes  by  frost  is  due  to  the  expan- 
sive force  of  ice.  If  the  free  water  in  cement-mortar  freezes  before  it  be- 
comes combined  by  crystallization .  in  the  process  of  hardening,  evidently 
this  mortar  cannot  set  or  harden  until  the  ice  melts.  But  when  the  tem- 
perature is  low  or  near  that  of  freezing  the  hardening  action  is  very  small,  so 
that  the  mortar  is  likely  to  dry  out  before  the  water  present  is  taken  up  by 
the  hardening  cement.  In  this  case  it  will  never  harden,  and  this  is  apt  to  be 
the  case  with  the  outer  or  exposed  portions  of  cement-masonry.  Again,  when 
the  cement  has  set  and  partially  hardened,  if  the  freezing  of  the  remaining 
water  (or  of  that  which  the  porosity  of  the  mortar  allows  to  enter  it  from 
without)  produces  an  expansive  force  in  excess  of  the  cohesive  strength  of 
the  mortar  at  the  time,  then  the  bond  is  broken  by  the  expanding  ice,  and 


614 


THE  MATERIALS  OF  CONSTRUCTION. 


on  thawing  out  the  mortar  crumbles  from  the  disintegrating  action  of  the 
frost,  the  same  as  a  soft,  porous  stone  or  brick  will  do.  Portland -cement 
mortar  being  stronger  than  that  made  with  natural  cement,  it  resists  this 
disintegrating  action  better,  and  hence  the  general  assumption  that  Portland 
cement  may  be  used  in  freezing  weather  and  natural  cement  may  not. 


30 


71 


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/    At 


H 


—  o—  c 


-  O 


A' 


3 


FIG.  555. — Filtration  of  Sea-water  through  1  cu.  ft.  of  Portland-cement  Concrete,  Three 
Months  Old,  under  24  ft.  head.     (Inst.  Civ.  Engrs.,  vol.  evil.  p.  95.) 

The  Universal  Rule  to  be  followed  when  using  cement  in  freezing  weather 
is  to  use  the  minimum  amount  of  water  in  gauging  the  mortar,  to  keep  it 
from  freezing  until  it  has  acquired  a  considerable  strength,  and  to  protect  it 
from  the  weather  or  from  the  action  of  alternate  wettings  and  freezings.  It 
should  also  be  made  richer  in  cement  than  that  used  at  ordinary  tempera- 
tures. There  are  various  ways  of  preventing  freezing,  as,  for  example : 


TESTS  ON  CEMENTS,   CEMENT-MORTARS,  AND   CONCRETES.      615 


1.  Warming  the  water  or  sand  or  stone,  or  all  of  them,  as  occasion  seems 
to  require. 

2.  In  very  cold  weather,  in  addition  to  the  provisions  in  (1),  the  work 
may  be  covered  with  earth  or  manure,  or  housed  and  a  fire  maintained,  etc* 

3.  In  place  of  these  methods  of  maintaining  a  temperature  above  the 
freezing-point,  the  water  may  be  dosed  with  salt  or  glycerine  or  alcohol, 
until  it  will  not  freeze  at  the  temperatures  anticipated. 

All  of  these  methods  are  used  and  all  are  satisfactory.  The  cheapest  and 
most  common  method  is  to  make  a  brine  of  the  water  used  in  gauging  the 
mortar.  In.  Fig.  556  the  proper  percentages  of  salt,  glycerine,  and  alcohol 


3d 


2$ 


y 

0° 


P£fl 


CENT 


O 


F 


O 


LUT 


rc 


N 


O  20  40  60  80 

FIG.  556. — Effect  on  the  Freezing-point  of  Cement  of  Various  Proportions  of  Glycerine, 
Alcohol,  and  Salt.     (Tetmajer,  vol.  vn.  p.  85.) 

are  shown  to  prevent  freezing  at  the  various  temperatures  from  32°  to  0°  F. 
From  this  it  appears  that  salt  is  the  most  efficient  agent  as  well  as  the 
cheapest.  From  this  diagram  we  have,  approximately, 

No.  degrees  F.  freezing  temp,  is  reduced  =  per  cent  salt  used. 

Thus  if  it  is  assumed  that  the  temperature  will  not  fall  below  22°  F.,  then 
10  per  cent  (by  weight)  of  salt  should  be  added  to  the  water.  If  a  tempera- 
ture of  10°  F.  is  to  be  provided  for,  use  22  per  cent  of  salt.  Doubtless  a 
less  proportion  of  salt  would  prove  effective  at  these  temperatures,  especially 
with  concrete  in  large  masses,  as  the  chemical  reactions  which  accompany 
the  hardening  of  the  cement  develops  a  considerable  amount  of  sensible  heat. 
(See  Art.  312  and  Figs.  333  and  333«.) 

Any  cement  sets  very  much  slower  at  a  low  temperature  than  at  a  higher, 
as  is  shown  by  Fig.  557,  which  is  complementary  to  Fig.  333,  p.  41-4.  Thus 
a  mortar  which  will  set  completely  (by  the  method  of  testing  employed) 
in  four  hours  at  a  temperature  of  35°  C.  (95°  F.)  would  require  twenty 
hours  at  5°  C.  (41°  F.)  and  thirty-eight  hours  at  0°  C.  (32°  F.).  In 
estimating  the  time  required  for  setting,  therefore,  this  temperature-effect 
must  be  allowed  for. 

In  Fig.  558,  upper  half,  is  shown  the  effect  of  salt  on  tension  briquettes 


616 


THE  MATERIALS  OF  CONSTRUCTION. 


of  Portland  cement  which  were  moulded  in  a  room  where  the  temperature 
was  8°  F.  (24°  F.  below  freezing),  and  where  the  briquettes  were  frozen  hard 
in  half  an  hour,  and  remained  frozen  60  days.  They  remained  in  the  open 
air  and  hardened  when  they  thawed  out.  It  should  be  noted  that  the 
briquettes  grew  weaker  between  the  ages  of  6i  and  9|  months. 

In  the  lower  half  of  this  figure  are  given  the  results  of  tests  of  the  same 
cement-mortar  moulded  in  air  at  a  temperature  of  21°  F.,  and  left  frozen 
for  three  days  and  then  placed  under  water  for  the  remaining  period. 


In  the  former  series  (hardened  in  air)  we  might  conclude  that  more  than 
5  or  10  per  cent  of  salt  weakened  the  mortar  somewhat,  while  in  the  latter 
(hardened  in  water)  the  briquettes  increased  in  strength  up  to  20  per  cent 
salt.  This  is,  furthermore,  a  more  typical  case.  Cement-masonry  is  not 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND   CONCRETES.      617 

likely  to  be  laid  in  extremely  cold  weather  or  when  such  weather  is  likely 
to  occur  before  the  cement  has  set. 

The  worst  set  of  conditions  for  cement-mortar  to  withstand  is  that  of  a 
succession  of  temperatures  below  and  above  the  freezing-point.  If  the 
mortar  freezes  as  soon  as  laid,  there  is  no  bond  to  be  broken,  and  no  injury 
can  result  provided  that  when  it  thaws  out  it  remains  unfrozen  long  enough 
to  harden.  But  if  it  begins  to  set  and  then  freezes  again  before  the  cohesive 
strength  can  resist  the  expansive  force  of  the  frost,  then  it  is  cracked  and 
these  severed  surfaces  will  never  again  unite.  Water  then  enters  such 
cracks  and  further  disintegration  follows. 


FIG.  558.— Effect  of   Salt  on  Portland-cement  Mortar,  1  C.:  2  S..  made  in  Freezing 

Weather.     (Wheeler,  Rep.  Chf.  Engrs.  1895,  p.  2968.) 

* 

A  careful  distinction  must  be  drawn  between  contraction  cracks,  which 
may  always  be  found  in  long  masonry  walls  in  cold  weather,  and  disentegra- 
tion  cracks  from  the  expansive  force  of  water  freezing  on  the  interior. 

In  Fig.  559  the  effect  of  salt  on  the  strength  of  both  natural-  and  Port- 
land-cement mortar  is  shown.  These  briquettes  were  not  subjected  to  freez- 
ing temperatures,  and  hence  the  results  are  not  very  significant.  These  and 
similar  tests  simply  determine  whether  or  not  the  salt  weakens  the  mortar  if 
used  at  temperatures  above  freezing.  But  as  it  is  never  used  in  this  way  the 
results  are  scarcely  to  the  point. 

Similar  to  these  are  the  results  shown  in  Fig.  5 GO,  except  that  all  these 
were  made  with  a  saturated  solution  of  salt  (about  30  per  cent),  and  with 
different  proportions  of  sand,  up  to  2  S.  :  1  C.,  which  is  as  much  sand  as 
should  be  used  in  freezing  weather. 


618 


THE  MATERIALS  OF  CONSTRUCTION. 


FIG.  559.— Effect  of  Salt  on  Strength  of  Cement-mortar  Six  Months  Old.     (Jour.  Assoc, 

Eng.  Socs.,  vol.  ix.) 


600 


//V 


MO  WTHS 


FIG.  560.—  Tensile  Strength  of  Quartz  FIG.  561.— Effect  of  Salt  on  Portland-cement 

and  Sand  Mortars  with  a  Saturated  Mortar,  1  C.  :  2  S.,  made  in  Freezing  Weather. 

Solution  of  Salt.     (R.  R.  Gazette,  (Wheeler,  Rep.  Chf.  Engrs.  1895,  p.  2971.) 
1892.) 


TESTS  ON  CEMENTS    CEMENT-MORTARS,  AND   CONCRETES.      619 

In  Fig.  5G1  we  have  the  extreme  conditions  of  fresh  water  and  a  brine 
containing  20  per  cent  salt,  used  in  making  up  Portland-cement-mortar 
briquettes  in  a  room  temperature  of  13°  to  16°  F.  (at  which  the  20-per-cent 
salt-mixtures  would  not  freeze),  and  left  at  this  temperature  for  three  days. 
Then  40  of  these  briquettes  were  placed  in  water  and  the  remaining  40  were 
stored  in  the  open  air.  This  being  early  in  January  at  Lake  Superior,  it  is 
likely  the  "  air  "  briquettes  remained  frozen  for  some  months.  When  they 
did  thaw  out,  the  temperature  conditions  seem  to  have  been  favorable  to  their 
hardening.  Probably  they  had  so  dried  out  while  frozen  that  there  was 


6       A&E          /A/ 

FIG.  562.— Use  of  Stilt  in  Portland-cement  Mortar,  1  C.  :  1  S.  and  1  C.  :  4  S.  Those 
left  in  air  remained  frozen  about  sixty  days.  Those  put  in  water  were  first  frozen 
in  air  three  days.  (Wheeler,  Rep.  C/if.  Engrs.  1895,  p.  2970.) 

not  sensible  moisture  enough  to  produce  expansion  by  successive  freezing 
and  thawing.  It  is  to  be  presumed  they  were  not  exposed  to  the  weather, 
but  were  at  least  under  shelter.  It  is  a  common  maxim  with  civil  engineers 
of  large  experience  in  such  matters  that  if  cement-masonry,  laid  in  freezing 
weather,  remains  frozen  till  dry,  or  if  it  "  freezes  dry,"  it  will  harden  with- 
out injury,  but  if  it  freezes  and  thaws  sucessively  while  yet  "green"  it  will 
be  injured,  if  not  ruined. 

In  Fig.  562  are  shown  results  on  two  mixtures,  1  C. :  1  S.,  and  1  C. :  4  S. 


620 


THE  MATERIALS  OF  CONSTRUCTION. 


These  briquettes  were  made  up  at  18°  F.  (at  which  temperature  the 
15-per-cent  salt-mixtures  would  scarcely  freeze),  and  the  "  air  "  briquettes 
put  in  the  "  open  air  "  after  three  days,  this  being  early  in  January,  1894, 
at  Lake  Superior.  Even  the  15-per-cent-salt  briquettes  doubtless  were 


frozen  on  being  put  out  in  the  open  air.     The  results  are  not  such  as  to  lead 
to  any  positive  conclusion. 

Prof,  von  Tetmajer  has  experimented  largely  with  anti-freezing  solutions 


TESTS  ON  CEMENTS,  CEMENT-MORTARS,  AND  CONCRETES.      621 

for  mixing  cement-mortars,  those  of  salt  on  Portland-cement  mortars  being- 
shown  in  Fig.  503,  and  on  natural-cement  mortars  in  Fig.  5G4.  All  these 
tests  were  made  at  the  standard  temperature  of  65°  F.,  so  that  they  show 
simply  the  effect  of  the  salt  on  the  tensile  and  the  compressive  strength, 
when  hardened  in  air  and  under  water.  In  every  case  any  addition  of  salt 
weakened  the  mortar,  an  addition  of  6  per  cent  of  salt  reducing  the  strength 


£00 


400 


30O 


200 


<?/       28        JJ      42       49 
TENSION. 


PIG.   564.—  Effect  of  Salt  on  the  Hardening  of  Natural-cement  Mortar    1  C  •  3  S. 

(Tetmajer,  vol.  vn.  p.  34.) 

about  25  per  cent.     The  reduction  was  more  marked  with  the  natural-  than 
with  the  Portland-cement  mortars. 

In  Figs.  565  and  565$  Tetmajer  gives  us  similar  results  on  Portland- 
cement  mortars  of  anti-freezing  mixtures  of  solutions  of  glycerine  and  of 
alcohol.  In  every  instance  these  ingredients  also  weakened  the  mortar. 


THE  MATERIALS  OF  CONSTRUCTION. 


TESTS  ON  CEMENTS,    CEMENT-MORTARS,   AND   CONCRETES.     623 

422.  Concrete    Mixtures    should   be   so  proportioned  as  to  produce  as 
nearly  as  possible  a  solid  mass  with  the  least  proportion  of  cement.   Broken 
stone  is  not  at  all  essential  to  a  first-class  concrete,  a  clean  gravel  serving 
quite  as  well.     Thus  Col.  G.  H.  Mendell  gives  the  followiig  formula  with 
the  resulting  volumes  at  each  stage*: 

Cubic  Feet. 

One  barrel  of  Portland  cement,  measured  loose 4.50 

Water  added 1.88 

Volume  of  paste > 3.90 

Sand  equal  to  three  times  the  volume  of  paste 10.70 

Water  added 2.25 

Volume  of  mortar , 11.21 

Gravel,  3/4  in.  and  less 36.70 

Volume  of  loose  concrete , , . . .  44.24 

Final  volume  tamped  in  place 36.20 

Here  we  have  51.9  cubic  feet  of  loose  solids  finally  compacted  to  a  volume 
of  36.2  cubic  feet,  or  to  69  per  cent  of  the  loose  volumes  when  measured 
separately. 

423.  Concrete  Structures  in  Sea-water.— On  the  subject  of  the  perma- 
nency of   cement-concrete  when    exposed  to   the  action  of  sea- water  Dr. 
Michaelis,  the  highest  possible  authority,  says  f  : 

"  The  main  points  to  be  considered  in  erecting  permanent  structures  in 
sea-water  with  the  aid  of  hydraulic  cements — in  other  words,  concrete — are : 

"  (1)  From  the  physical  point  of  view,  completely  impermeable  mixtures 
should  be  made,  composed  of  one  part  of  cement  with  two  or  at  the  most 
two  and  a  half  parts  of  sand,  of  mixed  grain,  of  which  at  least  one  third 
must  be  very  fine  sand.  To  this  the  requisite  quantity  of  gravel  and  ballast 
should  be  added.  This  impermeable  layer  should  surround  the  porous 
kernel  on  all  sides  in  sufficient  thickness,  even  underneath.  It  would,  per- 
haps, be  unnecessary  waste  of  material,  in  the  case  of  thick  walls,  to  use 
the  impermeable  mixture  throughout;  but,  so  far  as  possible,  the  compact 
shell  and  the  poorer  kernel  should  be  made  in  one  operation.  Where  this 
is  not  possible,  and  the  shell  is  added  subsequently,  numerous  iron  ties 
should  be  used. 

"  (2)  From  the  chemical  point  of  view,  cements  or  hydraulic  limes  rich 
in  silica,  and  as  poor  as  possible  in  alumina  and  ferric  oxide,  should  be  used, 
for  aluminate  and  ferrate  of  lime  are  not  only  decomposed  and  softened 
rapidly  by  sea-water,  but  they  also  give  rise  to  the  formation  of  double  com- 
pounds which  in  their  turn  destroy  the  cohesion  of  the  mass  by  producing 
cracks,  fissures,  and  bulges.  The  salts  contained  in  sea-water,  especially  the 
sulphates,  are  the  most  dangerous  enemies  of  hydraulic  cements.  The  lime 

*  In  Jour.  Assc.  Eng.  Socs.,  vol.  xiv.  p.  243. 
f  In  Trans.  Inst.  Civ.  Engrs. ,  vol.  cvn.  p.  375. 


624  THE  MATERIALS  OF  CONSTRUCTION. 

is  either  dissolved  and  carried  off  by  the  salts,  and  the  mortar  thus  loosened, 
or  the  sulphuric  acid  forms  with  it  crystalline  compounds  as  basic  sulphate 
of  lime,  alumino-sulphate  and  ferro-sulphate  of  lime,  which  are  segregated 
forcibly  in  the  mortar,  together  with  a  large  quantity  of  water  of  crystalliza- 
tion, and  a  consequent  increase  in  volume  results.  The  separation  of  hy- 
drate of  magnesia  is  only  the  visible  but  completely  innocuous  sign  of  these 
processes.  The  magnesia  does  not  in  any  way  enter  into  an  injurious  reac- 
tion with  silica,  alumina,  or  ferric  oxide;  it  is  only  displaced  by  the  lime 
from  its  solution  in  the  shape  of  a  flocculent,  slimy  hydrate  which  may  be 
rather  useful  in  stopping  the  pores,  but  can  never  cause  any  strain  or  ex- 
pansion, even  if  it  subsequently  absorbed  carbonic  acid. 

"  The  carbonic  acid,  whether  derived  from  air  or  water,  assists  the  hy- 
draulic cement  as  a  preservative  wherever  it  comes  into  contact  with  the 
solid  mortar.  It  could  only  loosen  the  latter  if  present  in  such  an  excess 
that  bicarbonate  of  lime  might  be  formed. 

"  (3)  The  use  of  substances  which  render  the  mortar,  at  any  rate  in  its 
external  layers,  denser  and  more  capable  of  resistance.  Such  substances  are: 
"  (a)  Sesquicarbonate  of  ammonia  (from  gas-liquor)  in  all  cases  where 
long  exposure  to  the  air  is  impossible.  Such  a  solution,  applied  with  a 
brush  or  as  a  spray  and  then  allowed  to  dry,  converts  the  hydrate  of  lime 
into  carbonate  of  lime.  The  latter  is  not  acted  upon  by  the  neutral  sul- 
phates present  in  sea-water.  It  must  be  repeated  that  it  is  a  decidedly  errone- 
ous opinion  that  the  texture  of  otherwise  sound  cements  is  injured  by  the 
action  of  carbonic  acid ;  on  the  contrary,  it  renders  them  more  capable  of 
resistance,  except  in  the  above-mentioned  case,  which  is  extremely  rare 
when  bicarbonate  of  lime  is  formed  and  goes  into  solution. 

"  (b)  Fluosilicates,  among  which  magnesium  fluosilicate  is  most  to  be 
recommended.  The  fret  lime  is  converted  into  calcium  fluoride  and  silicate 
of  lime,  and,  in  conjunction  with  the  liberated  hydrate  of  magnesia,  these 
new  products  close  the  pores  of  the  mortar.  Both  salts  are  sufficiently 
cheap  to  be  used  on  a  large  scale. 

"  (c)  Last,  not  least,  barium  chloride.  Two  or  three  per  cent  of  the  weight 
of  the  cement  is  dissolved  in  the  water  with  which  the  concrete  is  mixed. 
This  forms  perfectly  insoluble  barium  sulphate  with  the  sulphates  of  the 
sea-water,  while  the  magnesia  remains  in  solution  as  magnesium  chloride. 
Although  in  this  case  there  can  be  no  further  closing  of  the  pores,  yet  the 
insoluble  barium  sulphate  which  is  formed  affords  some  protection  and  does 
not  give  rise  to  any  increase  of  volume  (swelling).  From  two  to  three  per  cent 
of  barium  chloride  does  not  in  any  way  diminish  the  strength,  as  has  been 
'proved  by  means  of  comparative  tests  of  English  and  German  cements. 
Frequently  the  strength  of  the.  mortar  is  increased  by  this  addition.  This 
substance  is  only  to  be  used  in  the  external,  perfectly  water-tight  skin  of  the 
concrete;  in  other  words,  in  the  4-  to  8-inch  coating,  composed  of  1  cement, 
1  to  2  sand,  and  3  to  4  coarse  gravel,  flint,  broken  stone,  etc." 


TESTS  ON  CEMENTS,    CEMENT-MORTARS,   AND   CONCRETES.      625 

TABLE    XXXVIII.— TESTS    OF   THE    FIRE-RESISTING    QUALITIES    OF  DIFFERENT 

KINDS    OF    CONCRETE. 
(Hamburg  Commission  Report,  1895.) 


Num- 
ber of 

Test. 

Composition  ol 
Concrete. 

Time  o 
Heat- 
ing. 

Manner  ol 
Cooling. 

Result  of  Heating. 

Result  of 
Wetting  after 
Heating. 

Temperature 
measured  by 
Pyrometer. 

I. 

1  part  cement, 
7    parts    river 
gravel. 

1  part  cement, 
8    parts    river- 
gravel. 

m 

Suddenly. 

Broken. 

Crumbled     en 
tirely. 

Highest    tempera- 
ture 1060°  C. 

Slowly. 

*  * 

« 

II. 
III. 

m 

Suddenly. 

" 

« 

Slowly. 

" 

" 

M 

1  part  cement, 
3  parts  sand, 
5  parts  broken 
stone. 

3% 

Suddenly. 

Not  broken,  but  mortal 
very  tender. 

Lost  coherence 

Slowly. 

" 

'• 

« 

IV. 

1  part  cement, 
7  parts  washed 
bank-gravel. 

m 

Suddenly. 

Showed  very  little  co- 
herence. 

" 

Slowly. 

" 

» 

V 

VI. 

1  part  cement, 
8  parts  washed 
bank-gravel. 

1 

Suddenly. 

" 

Crumnled. 

After  1  hour  780°  C. 

Slowly. 

" 

" 

» 

[  part  cement, 
7  parts  fine  cin- 
der. 

1& 

Suddenly. 

Not  broken,  but  broke 
upon  striking. 

Showed     good 
coherence; 
did  not  suffer. 

After     \y4     hours 
780°  C. 

Slowly. 

" 

" 

Highest     tempera- 
ture 1080°  C. 

VII. 
VIII. 

1  part  cement, 
8  parts  fine  cin" 
der. 

m 

Suddenly. 

" 

" 

After     \y±     hours 
780°  C. 

Slowly. 

" 

" 

Highest    telhpera- 
ture  1080°  C. 

1  part  cement, 
7  parts  coarse 
cinder. 

3% 

~3^r 

~m~ 

Suddenly. 

^ot    broken  ;    showed 
relatively  the  highest 
degree  of  coherence, 
particularly    in     the 
centre. 

Did  not  suffer. 

lowly. 

" 

11 

" 

IX. 

X. 

1  part  cement, 
3  parts  coarse 
cinder. 

uddenly. 

" 

" 

Highest    tempera- 
ture 940°  C. 

lowly. 

" 

Did  not  suffev; 
friable  edges. 

" 

1  part  cement, 
3  parts  sand, 
5  parts  broken 
basalt. 

uddenly. 

ot  broken,  but  broke 
upon  striking. 

Crumbled. 

' 

lowly. 

Broken. 

Coherence  very 
slight. 

" 

XI. 

part  cement, 
"  parts  sand. 

3^ 

uddenly. 

Broken  in  3  pieces. 

Low  degree  of 
coherence. 

tt 

lowly. 

Broken  ;  very  tender. 

" 

XII. 

•  parts   Trass- 
mortar,* 
)  parts  cinder 

3^ 

uddenly. 

Broke  in  taking  out. 

Crumbled  com- 
pletely. 

'• 

3^ 

ovvly. 

Broken  ;  very  tender. 

" 

XIII. 

\ 

part  Trass, 
I  parts  slacked 
lime, 
'0  parts  river- 
gravel. 

uddenly. 

Completely  broken. 

" 

owly. 

Crumbled  to  powder. 

" 

*  Trass-mortar  =  1  part  Trass,  2  parts  slacked  lime,  3  parts  sand. 


626  TEE  MATERIALS  OF  CONSTRUCTION. 

TESTS   OF   THE    FIRE-RESISTIXG    QUALITIES    OF   CONCRETE — continued. 


Num- 
ber of 
Test. 

Composition 
of  Concrete. 

Time  of 
Heat- 
ing. 

Manner  of 
Cooling. 

Result  of  Heating. 

Result  of 
Wetting  after 
Heating. 

Temperature 
measured  by 
Pyrometer. 

XIV. 

1  part  cement, 
7  parts  pumice- 
sand. 

3& 

Suddenly. 

Not  broken  ;  showed 
some  coherence,  par- 
ticularly in  centre. 

Outer  part  ten- 
der, and  pieces 
fell  off. 

Highest   tempera- 
ture 940°  C. 

Slowly. 

Not  broken. 

Friable  on 
edges. 

M 

XV. 

1  part  cement, 
3  parts  sand, 

3^ 

Suddenly. 

Fell  to  pieces  upon 
touching. 

Crumbled     en- 
tirely. 

" 

stone. 

Slowly. 

Broken.    Coherence  al- 
most completely  lost. 

" 

XVI. 

7     courses     of 
brick        (one 
brick     deep) 
in       cement- 

'^ 

Suddenly. 

Mortar  very  tender 
and  lost  its  binding 
power:  some  bricks 
cracked. 

Slowly. 

it 

*  Cement-mortar  1  to  3. 

424.  The  Fire-resisting  Qualities  of  Concretes. — Since  concrete  con- 
struction is  now  used  very  largely  in  large  buildings,  its  fire-resisting 
qualities  become  of  supreme  importance  in  such  works.  The  most 
elaborate  investigations  ever  made  into  these  qualities  of  various  concrete 
mixtures  was  carried  out  by  a  commission  especially  appointed  by  the  city 
of  Hamburg,  Germany,  for  this  purpose  some  years  ago,  and  who  issued  an 
elaborate  report  in  1895.*  Table  XXXVIII  embodies  their  results  on  fire- 
tests  of  sixteen  different  concrete  mixtures. 

It  will  be  observed  that  all  the  sand,  gravel,  stone,  and  fine-cinder  con- 
cretes failed  to  stand  the  test.  Only  the  coarse-cinder  concrete  (1  C.  to  7 
or  8  cinder)  gave  good  results.  Even  the  wetting  while  hot  did  not  affect 
it.  It  would  seem,  therefore,  that  a  screened-cinder  concrete  would  give 
excellent  results. 

Hydraulic  cements,  both  natural  and  Portland,  harden  by  a  process  of 
crystallization,  requiring  the  coobination  with  an  amount  of  water  equal  to 
some  15  per  cent  of  the  weight  of  the  pure  cement.  When  this  crystallized 
mass  is  highly  heated  the  water  of  'crystallization  is  driven  oft'  and  the 
cement  is  reduced  to  an  inert  mass  or  powder.  A  high  heat  long  con- 
tinued, therefore,  is  fatal  to  the  strength  of  all  cement  mortars  and  con- 
cretes. 

Mr.  J.  S.  Dobie  has  found  f  that  neat  Portland-cement  "briquettes  two 
months  old,  gradually  heated  to  1000°  F.  and  then  removed  from  the  fur- 
nace and  allowed  to  cool  in  the  air,  lose  about  10  per  cent  of  their  weight 

*  Results  of  tests  upon  various  kinds  of  patented  heat-insulating  systems  of  protect- 
ing the  iron  framework  of  a  building  are  also  given  in  this  report, 
f  In  the  Digest  of  Physical  Tests,  vol.  i.  p.  212  (1896). 


TESTS  ON    CEMENTS,    CEMEMT-MORTARS,  AND   CONCRETES.     627 

and  50  per  cent  of  their  tensile  strength.  If  heated  suddenly  to  1775°  F. 
and  cooled  in  the  air,  they  lost  10  per  cent  of  their  weight  and  80  per  cent 
of  their  strength,  the  results  in  both  cases,  however,  being  far  from  uni- 
form. When  plunged  in  water  on  removing  them  from  the  furnace,  they 
fell  to  pieces  in  both  instances. 

Mr.  T.  T.  Johnston  has  shown  *  that  for  natural-  and  Portland-cement 
briquettes,  both  neat  and  1  C.  :  1  S.,  heated  to  a  dull  red  after  thorough 
drying,  gave  losses  of  strength  as  follows: 

LOSS   OF   STRENGTH    OF   CEMENT-MORTAR   FROM   HEATING. 


Kind  of  Cement. 

Neat. 

Mortar. 

Natural  cement  .       

89  per  cent 

(1  C 

1  S  )  Gl  per  cent 

Portland  cement 

58    " 

(1  C 

3  S  )  70    "      '' 

It  is  evident,  therefore,  that  fire-proof  construction  should  not  rely  on 
a  sand  or  stone  cement-concrete  for  tensile  strength.  If  it  be  used  only  in 
compression,  a  metal  base  resisting  the  tensile  deformations,  then  it  may  be 
able  to  carry  its  load  during  the  fire,  but  it  would  probably  require  recon- 
struction afterwards,  especially  if  water  reached  the  cement  portions  while 
they  were  highly  heated. 

425.  Portland-cement  Cinder-concretes. — The  strength,  weight,  cost, 
and  economy  of  a  Portland-cement  cinder-concrete  construction  in  St.  Louis 
in  1896,  taking  actual  prices  for  large  buildings  and  adding  5.5  cts.  per  cubic 
foot  for  laying,  are  shown  graphically  in  Fig.  566.  The  test  mixtures  were 
made  without  special  care,  and  had  therefore  much  less  strength  than  the 
same  ingredients  would  have  in  practice  if  mechanically  mixed. f  The  mix- 
tures are  arranged  in  the  diagrams  in  the  order  of  their  economic  values,, 

that  is,  in  the  order  of  their  rank  in  the  quality,  -  -  .     The  specimens 

cost 

were  all  6  in.  square  and  12  in.  high,  and  were  crushed  in  the  direction  of 
the  longest  dimension.  They  were  all  30  days  old  when  tested.  The 
cinders  were  the  ordinary  furnace  product  of  St.  Louis,  obtained  by  burn- 
ing the  Illinois  bituminous  coal  under  boilers.  It  is  mostly  a  fine  ash  with 
considerable  unburned  coal  in  its  composition. 

It  will  be  observed  that  the  mixture  1  cement  :  1  sand  :  3  cinder  is  at  once 

both  the  most  economical,  I  —  -  —  max.  J  and  also  the  strongest  for  its 

*  Engineering  Record,  vol.  xxxv.  p.  54. 

f  The  specimens  we'1*1  prepared  under  the  direction  of  Mr.  A.  L.  Johnson,  Assoc.  M, 
Am.  Soc.  C.  E.,  and  were  tested  by  the  author. 


628 


THE  MATERIALS  OF  V 


vpiffht    fstrength  =  max.^1     It  would  seem,  therefore,  that  where  quantity 

'   \  weight 

is  proportioned  to  obtain  a  given  strength,  this  would  be  the  mixture  to  em- 
ploy if  cinder-concrete  were  to  be  used. 


COMPOSITION  OF  CONCRETE  MIXTURES. 

FIG.  566.— Portland-cement  Cinder-concrete.     Strength,  Weight,  Cost,  and  Economy 
of,  for  St.  Louis,  1896.    Tests  made  by  the  Author. 


TESTS  ON  CEMENTS,    CEMENT-MORTARS,  AND   CONCRETES.      629 


TABLE  XXXIX. — CROSS-BENDING  STRENGTH  OF  PORTLAND-CEMENT  CINDER- 
CONCRP:TE  MIXTURES  WITH  AND  WITHOUT  EXPANDED  METAL  BASE. 

Slabs  36  in.  long,  12  in.  wide,  and  4  in.  thick  tested  as  beams  on  supports  32  in.  apart. 

(Author's  Records.) 


Mixture. 

With  or 
Without  Ex- 
panded 
Metal  Base. 

Modulus  of 
Elasticity, 
Pounds  per 
Square  Inch. 

Modulus  of 
Rupture, 
3wl 
f~2  bh* 
Pounds  per 
Square  Inch. 

Modulus  of 
Strength  at 
the  Apparent 
Elastic  Limit, 
Pounds  per 
Square  Inch. 

Total  Deflec- 
tion under 
Maximum 
Load, 
in  Inches. 

1   cement  °  5  cinder 

With 

970,000 

150 

150 

0.008 

1         "       -5        '       

Without 

3-20,000 

550 

300 

.450 

1         "       -6        ' 

Without 

490,000 

150 

150 

.015 

1         "      :  6        ' 

With 

930  000 

450 

200 

'100 

1  cement  :  1  sand  :  1  cinder 

Without 

690,000 

170 

150 

'.015 

1         "      :1             :1 

With 

1,930,000 

465 

200 

.130 

1         "       :2             :5 

Without 

430,000 

100 

100 

.002 

1         "      :  2             :  5 

With 

800,000 

575 

300 

.169 

1         "      :3            :5 

Without 

490,000 

88 

75 

.013 

1         "      :3            :5 

With 

510,000 

370 

200 

.142 

1         "      :1            :6 

Without 

260,000 

100 

75 

.020 

1         "      :1             :6 

With 

540,000 

445 

150 

.158 

CHAPTER  XXXI. 
RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 

STONE.* 
426.  The  Structural  or  Building  Stones  consist  principally  of 

The  Granites  (including  the  Gneisses), 

The  Limestones  (including  the  Marbles),  and 

The  Sandstones  (including  Breccias  and  Conglomerates). 

The  granites  are  unstratified,  eruptive  rocks,  and  are"  composed  of  quartz 
(pure  silica,  Si02)  having  a  hardness  of  7;f  of  feldspar  (silica,  alumina, 
together  with  potash,  soda,  or  lime)  with  a  hardness  of  6 ;  hornblende,  hard- 
ness 5  to  G;  and  small  scales  of  mica  with  a  hardness  of  3  (see  Fig.  567). 

The  limestones  are  stratified  rocks  composed  of  sedimentary  or  chemical 
deposits,  of  which  the  carbonate  of  lime  forms  the  principal  ingredient. 
When  wholly  crystalline  and  suitable  for  ornamental  purposes  it  is  called 
marble  (Fig.  571).  When  it  is  composed  largely  of  a  double  carbonate  of 
lime  and  magnesia  it  is  properly  called  dolomite.  Some  of  the  marbles  also 
have  this  composition.  When  the  stone  is  composed  very  largely  of  small 
shell  fragments  it  is  called  oolitic  limestone,  Fig.  569  (from  its  resemblance 
to  the  roe  of  a  fish).  Onyx  is  a  kind  of  crystalline  limestone  which  has  been 
formed  wholly  by  chemical  deposition,  while  stalactite  and  stalagmite  forma- 
tions are  also  limestones;  but  they  should  never  be  confounded  with  onyx, 
however  much  they  may  resemble  it  when  polished. 

*  The  material  in  this  chapter  on  Stone  has  been  partly  drawn  from  Merrill's  Stones 
for  Building  and  Decoration  (Wiley,  New  York), 

f  The  following  scale  of  hardness  is  commonly  used  for  minerals: 

1.  Easily  scratched  with  the  thumb-nail,  as  talc. 

2.  Can  be  scratched  by  the  thumb-nail,  as  gypsum. 

3.  Not  readily  scratched  by  the  thumb-nail,  but  readily  cut  with  a  knife,  as  calcite 
(calcspar,  or  calcium  carbonate). 

4.  Can  be  cut  with  a  knife  less  easily  than  calcite,  as  fluorite  (fluor-spar). 

5.  Can  be  cut  with  a  knife  with  difficulty,  as  apatite. 

6.  Can  be  cut  with  a  knife  only  on  thin  edges,  as  feldspar. 

7.  Cannot  be  cut  with  a  knife  and  scratches  glass,  as  quartz. 

630 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


631 


FIG.  567.— Biotite  Granite,  of  Hallo-  FIG.  568.— Diabase  from  Weehavvken. 

well,  Me.  N.  J. 


FIG.  569.— Oolitic  Limestone,  Southern        FIG.  570.— Reddish  Potsdam  Sandstone 
Indiana  and  Northern  Kentucky.  New  York 


FIG  571.— Crystallized  Limestone  Fio.  572.— Brown  Triassic  Sandstone 

or  Marble  from  Vermont.  from  Portland,  Conn. 

Microscopic  Views  of  Building-stones.      Magnified  20  Diameters.      (From  Merrill's 
Stones  for  Building  and  Decoration,  1891.) 


032  THE  MATERIALS  OF  CONSTRUCTION. 

Sandstones  are  fragmental  rocks  composed  mostly  of  grains  of  silica 
(quartz)  which  have  been  cemented  together  by  a  deposition  of  silica, 
carbonate  of  lime,  iron  oxide,  or  clayey  matter.  If  the  cementing  material 
be  silica,  as  in  Fig.  570,  the  rock,  while  extremely  durable,  is  very  hard 
and  difficult  to  work.  Iron  oxide  in  the  cementing  material  gives  to  the 
stone  a  reddish  or  brownish  color,  as  shown  in  Fig.  572;  here  is  also  car- 
bonate of  lime  and  clayey  matter,  while  the  sand-grains  are  composed  of 
both  quartz  and  feldspar,  this  latter  being  indicated  in  the  figure  by  the 
grains  marked  by  parallel  bands.  This  more  porous  and  absorbent  matrix 
is  conducive  to  disintegration  by  water  and  frost,  although  such  a  stone  is 
readily  worked  and  has  been  very  largely  used  in  America.  The  most 
durable  sand-stones  (having  the  silica  matrix)  are  so  hard  to  work  that 
other  kinds  of  durable  rock  are  generally  preferred.  When  the  sand-grains 
are  so  lightly  attached  that  they  will  readily  crumble  they  may  be  used  as 
grindstones,  as  the  sandstone  of  northern  Ohio  near  Cleveland. 

427.  The  Weathering  of  Building-stones. — This  term  includes  the  resist- 
ance of  stones,  when  exposed  to  the  weather,  to  all  the  disintegrating  actions 
of  heat  and  cold,  water,  frost,  and  chemical  action,  which  combine  in  this 
climate  to  effect  the  rapid  decomposition  and  destruction  of  most  of  the 
rocks,  and  of  many  of  those  which  have  been  selected  for  building  purposes. 
A  stone  building  or  monument  should  remain  in  good  preservation  for  hun- 
dreds of  years,  but  more  commonly  they  begin  to  scale  and  crumble  before 
they  are  twenty-five  years  old.  The  life  of  a  rock  may  be  many  thousands 
of  years  in  Egypt,  or  Italy,  or  Greece,  when  it  would  not  last  as  many  scores 
of  years  in  the  United  States. 

"The  chief  disintegrating  agent  with  the  relatively  impervious  rocks  is 
probably  the  variation  of  temperature,  thus  breaking  the  bond  by  continual 
expansions  and  contractions,  while  with  the  more  porous  and  absorbent  it  is 
probably  the  freezing  of  the  absorbed  water.  However,  these  two  causes 
usually  combine  in  this  climate. 

By  far  the  best,  and  perhaps  the  only  infallible,  test  of  the  weathering 
qualities  of  any  given  rock  is  the  examination  of  a  ledge  of  it  which  has  been 
long  exposed,  or  of  an  old  building,  slab,  or  monument  of  the  stone  from  the 
same  quarry  and  ledge.  Sedimentary  rocks,  such  as  the  limestones,  may 
differ  radically  in  consecutive  ledges,  so  that  here  the  particular  course,  or 
ledge,  must  be  identified.  As  this  test  cannot  be  applied  to  a  new  quarry 
without  an  exposed  face,*  and  because  this  is  by  far  the  most  important 
quality  of  any  building-stone,  attempts  have  long  been  made  to  formulate 
artificial  tests  of  this  quality,  but  without  any  very  marked  success.  A 
single  illustration  of  actual  weathering  for  many  years  is  worth  more  than 

*  North  of  the  Ohio  and  Missouri  rivers,  where  the  face  of  the  country  has  been 
scoured  by  glacial  action  these  rock-exposures  are  common.  Where  the  glacial  erosion 
did  not  occur  no  sound  rock-exposures  should  be  expected.  In  the  glaciated  region 
the  scratches  and  grooves  of  the  glaciers  are  still  plainly  visible  in  many  places. 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


633 


.0500 


0400 


,0300 


,0200 


.0/00 


7 


2 


\ 


all  the  artificial  tests  which  can  be  applied. 
Nevertheless,  when  these  cannot  be  had,  some- 
thing may  be  done  in  the  way  of  determining 
relative  resistance  to  frost,  as  described 
below. 

428.  Freezing  Tests. — Specimens  of  the 
stone  may  be  saturated  with  water  and 
frozen  and  thawed  say  twenty-five  times, 
after  which  the  loss  in  dry  weight  and  the 
loss  in  crushing  strength  may  be  determined. 
This  is  the  method  pursued  by  Prof.  Bau- 
schinger.  The  loss  in  weight  by  this 
method  is  so  insignificant  (see  Fig.  573)  as 
to  furnish  a  very  small  base  from  which  to 
estimate  the  relative  weathering  qualities  of 
the  stone.  At  best  it  is  but  a  comparative 
test,  the  results  of  tests  on  various  kinds  of 
stone  being  compared  with  each  other.  The 
test  for  strength  after  freezing  is  also  quite 
as  unsatisfactory,  since  here  comparison 
must  be  made  between  different  specimens 
of  the  same  stone,  and  a  safe  conclusion 
would  have  to  rest  upon  average  results 
of  a  large  number  of  tests,  and  the  results 
would  still  be  only  relative. 


0) 

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• 

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PIG.  573.— Comparative  Tests  of  Building-stones  by  Freezings  and  by  the  Sulphate-of- 
soda  Test.     (Trans.  Am.  Soc.  C.  E.,  vol.  xxxni.  p.  242.) 


634  THE  MATERIALS  OF  CONSTRUCTION. 

429.  The  Sulphate-of-soda  Test  (Brard's  process  *)  consists  in  immersing 
the  specimens  for  a  short  time  in  a  boiling  solution  of  the  sulphate  of  soda, 
in  the  form  of  a  decahydrate,  commonly  known  as  Glauber's  salt  (NaaS04, 
10HaO),  and  then  suspending  them  in  the  air  for  a  day  in  order  that  the 
absorbed  salt  may  crystallize.  This  process  is  repeated  daily  for  a  week  or 
more,  and  then  the  dried  salt  is  dissolved  out  by  soaking  in  water,  frequently 
renewed,  for  a  week  or  more. 

In  making  this  test  it  is  important  to  have  a  solution  of  the  decahydrate 
which  is  saturated  while  cold  or  at  a  temperature  below  80°  F.  The  percent- 
age required  to  make  a  saturated  solution  increases  from  22  per  cent  at 
32°  F.  to  120  per  cent  at  90°  F.  At  about  100°  F.  the  salt  melts  in  its 
own  combined  water,  and  changes  to  the  anhydrous  form  (Na2S04),  and  at 
higher  temperatures  the  anhydrous  salt  dissolves  in  water  in  diminishing 
proportions,  reaching  12G  per  cent  at  212°  F.f.  In  cooling  and  drying,  the 
decahydrate  is  again  formed,  and  this  crystallizes  as  the  solution  dries  down 
below  the  saturation-point. 

As  the  disintegrating  action  of  this  test  is  manifested  wholly  on  the  sur- 
face, so  far  as  the  loss  of  weight  is  concerned  (the  specimens  being  washed 
after  each  drying),  it  is  important  that  the  specimens  tested  should  have 
the  same  superficial  area  per  unit  of  weight.  This  means  that  if  the  speci- 
mens are  of  the  same  shape  they  must  also  be  of  the  same  size.  A  better 
method  of  representing  the  results  would  be  to  give  the  loss  of  weight  per 
square  inch  of  surface,  rather  than  the  percentage  of  loss  in  weight  as  is 
commonly  given.  Thus  in  the  results  plotted  in  Fig.  573  the  specimens 
weighed  from  23  to  94  grams,  with  no  information  given  as  to  their  shape 
or  dimensions,  while  the  results  are  taken  out  as  percentages  of  loss  in 
weight.  Evidently  the  smaller  specimens  were  at  a  great  relative  dis- 
advantage, as  their  superficial  areas  would  be  much  greater  per  unit  of 
weight. 

If  the  granites  and  the  decomposed  sandstones  be  omitted  from  the  list 
of  stones  given  in  Fig.  573,  the  average  loss  of  weight  on  the  remainder  by 
the  sulphate-of-soda  test  is  about  six  times  that  by  the  freezing  test.]; 

The  specimens  should  either  be  heated  before  immersion  in  the  boiling 
liquid,  or  they  should  be  immersed  before  the  liquid  has  come  to  the  boiling 
temperature.  The  time  of  immersion  need  not  be  over  30  minutes,  after 
which  the  specimens  should  be  freely  suspended  in  the  open  air  for  24  hours. 
They  are  then  sprayed  from  a  wash-bottle  and  again  immersed  and  boiled, 
this  process  being  repeated  for  any  desired  number  of  times,  generally  from 
7  to  10.  The  specimens  should  be  small,  about  one-inch  cubes  being  a  suit- 

*  An.  de  Chem.  et  de  Phys.,  vol.  xxxvni.  p.  160,  1828,  afterwards  modified  by 
d'Hericart  and  de  Thury.  See  Trans.  Am.  Soc.  C.  E.,  vol.  xxxni.  p.  246. 

f  See  Fig.  21,  p.  133,  of  Newth's  Inorganic  Chemistry. 

\  This  agrees  with  comparative  results  obtained  by  Mr.  E.  Gerber,  Trans.  Am.  Soc. 
C.E.,  vol.  xxxni.  p.  253. 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


639 


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THE  MATERIALS  OF  CONSTRUCTION. 


TABLE    XL.  —  PHYSICAL    PROPERTIES    OF   BUILDING-STONES. 
Condensed  from  Merrill's  Stones  for  Building  and  Decoration. 


Kind  of  Stone. 

Locality. 

Position. 
1 

a 

u 

P.I-H 

CO 

Specific  Gravity. 

Weight  per  Cubic 
Foot. 

Percentage  of 
Absorption 
by  Weight. 

Number  of  Speci-  j 
mens  averaged.  J 

Ibs. 

Ibs. 

1.  Granite 

Grape  Creek,  Brownsville,  Law-) 
son,    Platte   Canon,  Cotopaxi,  v 
Mouarch,  Guunison  —  Colo.        ) 

j  Bed 
(Edge 

15,531 
18,536 

2.68 

187.3 

1.1 

8 

2.  Granite 

New   London,   Millstone  Point,  "j 

Mystic  River,  Stony   Creek  — 

Conn.     Vinalhaven,    Fox    Isl- 

and, Dyer's  Island,  City  Point,  [ 
Dix  Island,  Jonesboro,  Spruce- 

Bed 

16,200 

2.65 

166.0 

0.4 

20 

head,  Hewitt's  Island,  Hurri- 

cane  Island  —  Maine.      Huron 

Island—  J/icA.                               j 

3.  Granite 

East   Saint  Cloud,  Saint  Cloud,) 
Watab,  Sank   Rapids,   Beaver  >• 
Bay  —  Minn. 

{Bed 

"/Edge 

24,464 
24,464 

2.65 

165.8 

0.5 

7 

4.  Granite 

Cape  Ann,  Rockport,  Quincy  —  ) 
Mass.                                            [ 

Bed 

16,079 

2.67 

167.0 

0.7 

4 

5.  Granite 

Fall      River,      Mpnson  —  Mass.  ~] 

Keene  —  N.  H.      Tarry  town, 

Morrisauia,      Staten      Island, 

North    River,    Madison    Ave-  }• 

Bed 

15,570 

2.69 

168.0 

0.4 

14 

nue,    Chaumont     Bay—  N.  Y.  \ 

Westerly  —  R.  I.      Richmond 

-Fa.                                           J 

6.  Granite 

New    Haven  —  Conn.     Duluth,  ") 

Taylor's  Falls,  Beaver  Bay— 
Minn.     Jersey    City   Heights,  [ 
Pompton—  N.  J.     Goose  Creek  | 

JBed 

1  Edge 

21,272 

20,740 

3.82 

176.2 

0.3 

6 

(Loudouu  County)—  Fa.            J 

7.  Limestone 
(oblitic) 

Putnamville,  Greensburgh,  Saint) 
Paul,  Harrison  County,  Mount  [ 

Bed 

14,054 

156.2 

1.4 

6 

Veruou,  Bloomiugtou—  2nd.      } 

8.  Limestone 

Spencer,    Ellettsville,    Bedford,  ) 
Salem  —  2nd.                                j" 

Bed 

9,297 



145.9 

3.6 

8 

9.  Limestone 

Bardstown  —  Ky. 

JBed 

(Edge 

16,250 
15000 

2.67 

166.9 

1.2 

1 

10.  Limestone 

Lee  —  Mass. 

JBed 

22,323 

3 

(Edge 

21,728 

11.  Limestone 

Frontenac,   Stillwater,  Winona,) 
Red  Wing,   Kasota,   Mantor-V 
ville  —  Minn.                               J 

(Bed 

(Edge 

16,320 
16,643 

2.52 

157.3 

3.1 

7 

12.  Limestone 

Glens     Falls,  Lake   Champlain.1 

Canajoharie,  Kingston,  Garri-  1 
son's  Station,  Williamsville—  j 

JBed 
(Edge 

16,971 
15,533 

2.58 

168.1 

.... 

6 

(    i ' ' '• 

E  ANDBR{CK. 


RESULTS  OF  TESTS  OF  STONE 
PHYSICAL    PKOPERTIES    OF    BUILDIXG-STOXES— continued. 


641 


Kind  of  Stone. 

Locality. 

Position. 

ll 
52 

f! 

CO 

Specific  Gravity. 

Weight  per  Cubic 
Foot. 

Percentage  of 
Absorption 
by  Weight. 

Number  of  Speci- 
mens averaged.  | 

, 

Ibs. 

Ibs. 

13.  Limestone 
(marble) 

Montgomery  County  —  Pa. 

(Bed    1  13,112 

(Edge  11,055 

4 

14.  Limestone 
(marble) 

Dorset  —  Vermont. 

(Bed 

(  Edge 

10,506 
8,670 

2.64 
2.68 

164.7 
167.8 

2 
1 

15.  Limestone 
(marble) 

Italy. 

Bed 

12,1562.69 

168.2 



1 

16.  Sandstone 

Buckhorn  (Larimer  Co.),  Trim-") 

1 

dad  (Las  Auimas   Co.),  Mani- 

I 

tou    (El   Paso    Co.),   Ralston,  | 

Left  Hand,  Saint  Vairus,  Fort  }- 
Collins    (Larimer    Co.),    Stout 

(Bed 

\  Edge 

11,141 
12,434 

2.13 

132.9 

6.6 

9 

(Larimer  Co  }—Colo.     Thistle 

—  Utah. 

17.  Sandstone 

Coal  Creek,  Oak  Creek  (Fremont  1 

Co.),Guunison  (Guniiison  Co.),  1 

Manitou    (El    Paso    Co.),    La  V 
Porte    (Larimer    Co.),    Brand- 

(Bed 

]Edge 

5,481 
4,941 

2.12 

133.0 

13.8 

9 

ford  (Fremont  Co.)—  Colo. 

18.  Sandstone 

Middletown,    Portland  —  Conn. 

East    Long    Meadow  —  Mass.  • 

Bed 

6,639 

2.27 

142.2;   3.5 

3 

Marquette—  Mich. 

19.  Sandstone 

Hinckley,  Fort  Suelliug  —  Minn. 

{Bed     16,625 
(Edge  18,750 

2.38 

139.0    6.0 

2 

20.  Sandstone 

Dresbach,  Jordan,  Fond  du  Lac, 
Dakota  —  Minn.                            f 

{Bed       5,7891   QQ 
"(Edge    4,102i' 

124.4 

9.9 

6 

21.  Sandstone 

Taylors'    Falls,  Kasota,   Fronted 
uac  —  Minn.                                 f 

{Bed       7,4S39,0 
"(Edge    9,725^' 

142.4 

5.9 

3 

22.  Sandstone 

Haverstraw,  Hudson  River,  A1-) 
biou—  JY.  Y.                                f 

(Bed       8.925  9  ^ 
"(Edge    7,687| 

142.2    26 

2 

23.  Sandstone 

Medina—  .ZV.  T. 

(Bed     17,  500  2.  42  150.  8 
]Edge  14,812,2.39  149.3 

'    1.6 

2.0 

o 
1 

24.  Sandstone 

Verrnillion  —  Ohio. 

(  Bed       7,840' 
'{Edge    6,875  *A 

135.0 

5.2        ^ 

25.  Sandstone 

Seneca  —  Ohio. 

\  Edge  loisOO2'39 

149.3   3.1        1 

1 

26.  Sandstone 

Cleveland  —  Ohio. 

{Bed       6,8009  Q4 
(Edge    7,  91  Or- 

140.  0(  2.8 

1 

27.  Sandstone 

Marblehead  —  Ohio. 

j  Bed      7,937  0 
(Edge     6,850  *-6i 

144.4 

5.2 

1 

\ 

28.  Sandstone 

North  Amherst—  Ohio. 

(  Bed       6,212!2  -fi 
(  Edge    5,450i    ' 

133.7    .  o 
135.8    5'3 

2 
1 

29.  Sandstone 

Berea  —  Ohio. 

Bed       9,236  2.  IS 

133.  C 

>   5.5 

2 

642 


THE  MATERIALS  OF  CONSTRUCTION. 


therefore,  having  a  crushing  strength  of  3000  Ibs.  per  square  inch  is  quite 
strong  enough  for  all  ordinary  building  purposes,  the  strength  of  masonry 
being  measured  by  the  strength  of  the  mortar  used.  While  there  is  no  ob- 
jection to  greater  strength,  and  while  strength  may  be  some  evidence  of 
weathering  resistance,  yet  it  cannot  be  said  that  one  stone  is  better  than 
another  for  building  purposes  simply  because  its  crushing  strength  is 
20,000  Ibs.  per  square  inch,  whereas  the  strength  of  the  other  is  only 
5000  Ibs.  per  square  inch.  In  the  opinion  of  the  author  this  difference 
of  strength,  taken  alone,  has  no  significance  and  should  be  given  no 
weight. 


moo 


8000 


6000 


4000 


2000 


.OO3 

FJG.  57.7. — Elastic  Propeities  of  Various  Stones  under  Compressive  Stress.     (  Wat.  Ars. 

Rep.  1894.) 

435.  The  Elastic  Properties  and  Crushing  Strength  of  Building-stones. 

-Limestones  and  granites  are  nearly  perfectly  elastic  for  all  working  loads, 
while  sandstone  takes  permanent  sets  for  the  smallest  loads.  These  qualities 
are  well  illustrated  in  Fig.  574  for  limestone,  Fig.  575  for  granite,  and  Fig. 

576  for  sandstone.     These  figures  show  that  some  permanent  set  accompanies 
all  loads  even  on  the  limestones  and  granites,  but  these  are  extremely  small 
as  compared  to  those  on  the  sandstone.     Similar  results  appear  also  on  Figs. 

577  to  583. 

In  all  these  stress-diagrams  the  modulus  of  elasticity  may  be  taken  off  by 
extending  a  tangent  to  the  curves  at  the  origin  till  it  intersects  the  vertical 
line  marking  a  deformation  of  0.001  of  the  length.  The  corresponding  load 
in  pounds  per  square  inch,  taken  from  the  stress  argument,  when  multiplied 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


643 


"by  1000  gives  the  modulus  of  elasticity  in  compression.  Bauschinger  has 
shown  that  this  is  practically  the  same  as  that  obtained  from  bending  tests, 
and  hence  it  may  be  used  for  computing  the  deflection  of  stone  beams.  The 
moduli  of  elasticity  given  in  Table  XLI  are  those  found  in  cross-bending 
on  the  first  loading.  Bauschinger  gives  them  also  in  every  case  for 
tension  and  for  compression;  but  these  are  not  reproduced  here,  as  they 
are  practically  the  same  as  in  cross-bending.  By  comparing  the  results 
in  this  table  three  seems  to  be  no  general  or  fixed  relation  between  the 
various  kinds  of  strength  of  stone.  As  these  tests  were  made  with  the 
greatest  care  and  precision,  this  table  must  be  accepted  as  conclusive  on  this 
point. 


TABLE   XLI. — PROPERTIES    OF   THE   BUILDING-STONES   OF   BAVARIA. 
(Bauscbinger's  Communications,  vol.  x,  1884.) 


Kind  of  Stone. 

>> 

SJ 

5 
o 

«3 

1 

W 

Weight  per 
Cubic  Foot. 

Cross-bending. 

Compressive  Strength. 

Tensile  Strength. 

Shearing 
Strength. 

Modulus 
of 
Elasticity 

Mod- 
ulus of 
Rup- 
ture. 

Perpen- 
dicular 

to  Bed. 

19,200 
19,200 
8,130 
11,110 
4,664 
19,340 
1,195 
7,420 
9,040 
12,930 
6,160 
7,636 
6,681 
3,071 
3,029 
4,707 
13,510 
28,860 
5,546 

Parallel 
to  Bed. 

18,910 
20,050 
8,320 
7,410 
8,760 
20,620 
2,545 
6,010 
7,790 
13,410 
6,100 
8,390 
6,670 
2,247 
2,659 
4,308 
14,500 
17,490 
4,408 

Parallel 
to  Bed 
after  25 
Freez- 
ings. 

21,470 
20,480 
6,810 
12,290 
3,313 
18,770 
2,076 
6,730 
7,910 
11,520 
4,877 
•  5,986 
5,900 
2,161 
4,252 
4,038 

's',^6 

Perpen- 
dicular 
to  Bed. 

Par- 
allel 
to 
Bed. 

142 

853 
384 
540 
299 
1,138 
213 
355 
313 
540 
427 
284 
469 
242 
185 
327 
370 
768 

Granite  

2.65 
2.66 

2.48 
2.23 
2.08 
2  72 

i!so 

2.06 
2.20 
2.28 
2.00 
2.20 
2.23 
1.82 
1.92 
2.15 
2.60 
2.73 
2.29 

165.4 
166 
154.8 
139.2 
129.8 
169.7 
112.3 
128.5 
137.3 
142.3 
124.8 
137.3 
139.1 
113.6 
119.8 
134.2 
162.3 
170.4 
142.9 

2,986,000 
1,621,000 
6,420,000 

4,906,000 

'  426,600 
867,400 
1,340,000 
311,300 
910,000 
334,200 
512,000 
270,200 
583,000 
568,800 
2,687,000 
1,763,000 

1,365 
1,194 

882 

"462 
1,792 
469 
469 
718 
1,109 
341 
483 
441 
249 
135 
156 
597 
967 
654 

619 
683 
583 
448 
213 
910 
227 
107 
199 
576 
128 
341 
213 
9S 
67 
94 
327 
512 
242 

1,379 
1  ,450 
555 
739 
498 
1,479 
227 
569 
512 
910 
455 
640 
583 
370 
242 
341 
668 
995 

Triassic  limestone  ... 
Jurassic  limestone  (marble) 

Oolitic  limestone  
Tuffa  stone 

Variegated  sandstone  

Carboniferous  sandstone  
limestone  .  .  . 
Slaty  sandstone 

Green  sandstone  
Cretaceous  sandstone  

Quartz  conglomerate  

Iii  Table  XLII  we  have  given,  in  addition  to  the  usual  compressive 
strength,  the  modulus  of  elasticity  in  compression,  the  shearing  strength,  the 
ratio  of  lateral  to  longitudinal  deformation  from  stress  (Poisson's  ratio,  see 
Art.  5,  p.  5),  and  the  coefficient  of  expansion.  This  last  property  of  stone 
the  author  has  not  found  elsewhere,  and  as  it  is  a  very  important  one,  the 
table  has  great  value  for  this  alone.  The  coefficient  of  expansion  of  iron  and 
steel  is  about  0.0000005  (varying  from  0.0000050  to  0.0000070),  while  that 
of  stone  and  cement,  as  shown  by  this  table,  varies  from  about  0.0000020  to 
O.OOOOOGO.  Iron  or  steel  embedded  in  stone  masonry,  therefore,  would  have 
a  very  small  relative  expansion  and  contraction  from  temperature.  It  will 
be  noticed  that  Poisson's  ratio  varies  from  ^  to  £,  so  that  the  value  J, 


644 


THE  MATERIALS  OF  CONSTRUCTION. 
/QOOO 

8000 


T/OMfTl  COM/VIW8/ON 


0 


FIG.  578. — Elastic  Properties  of  Various  Stones  under  Compressive  Stress.     ( Wat.  Ars. 

Rep.  1894.) 


.00; 


.002 


.003 


FIG.  579.— Elastic  Properties  of  Various  Stones  under  Compressive  Stress.     (Wat.  Ars. 

Rep.  1894.) 


RESULTS  OF  TESTS   ON  STONE  AND  BUICK. 


645 


which  is  commonly  assumed   for   metals,  would  also  serve  very  well   for 
stone. 


TABLE      XLII. — TESTS 


OF      AMERICAN     BUILDING-STONE 
WATEKTOWX    ARSEXAL. 

(Rep.  1894.) 


MADE      AT      THE 


Name  of  Stone. 

.Veight 
pet- 
Cubic 
Foot. 

Compression  Tests. 

Ratio  of 
Lateral 
Expan- 
sion to 
Longi- 
tudinal 
Compres- 
sion.* 

Shearing 
Strength. 

Coefficient  of 
Expansion 
in  Water. 

Strength 
in  Pounds 
per  Square 
Inch. 

Modulus  of 
Elasticity  foi 
Working 
Loads. 

Brandford  granite  (Conn.).  .  . 
Mil  ford  granite  (Mass.)  

Pounds 
162.0 
162.5 

15.707 
23,775 

8,333,300 
6,663,000 

0.250 
0.172 

Pounds. 
1,833 
2,554 

2,214 
1,825 
1,550 
1,369 
1,237 
1,411 
1,242 

.00000398 
.00000418 
.00000415 
.00000337 

Troy  granite  (N.  H.)  
Milford  pink  granite  (Mass.). 
Pigeon  Hill  granite  (Mass.).  . 
Creole  marble  (Georgia).    .  .  . 
Cherokee  marble  (Georgia). 
Eiowah  marble  (Georgia)... 
Kennesaw  marble  (Georgia).. 
Lee  marble  (Mass  )  

164.7 
161.9 
161.5 
170.0 
167.8 
169.8 
168.1 

26,174 

18,988 
19,670 
13,466 
12,618 
14,052 
9,562 

4,545,400 
5,128,000 
6,666,700 
6,896,500 
9,090,900 
7,843,100 
7,547,100 

0.196 

0.345 
0.270 

0.278 
0.256 

.00000441 

.00000454 
.00000194 
.00000441 
.00000464 
.00000437 

Marble  Hill  marble  (Georgia) 
Tuckahoe  marble  (N  Y  ) 

168.6 
178.0 
139.1 

11,505 
16,203 
7,647 

9,090,900 
13,563,200 
3,200,200 

0.294 
0.222 
0.250 

1,332 
1,490 
1,705 

Mt.  Vernon  limestone  (Ky.).  . 
Oolitic  limestone  (Ind  )  

North  River  bluestone(N.Y.) 
Mouson  slate  (Maine).  ........ 



22,947 

5,268,  800 

.00000519 
.00000177 

Cooper  sandstone  (Oregon)  .  . 
Sandstone,  Cromwell  (Conn.) 
Maynard  sandstone  (Mass.).  .. 
Kibble  sandstone  (Mass).  ... 
Worcester  sandstone  (Mass).  . 

15*9.8 

183.5 

1384 
136.6 

15,163 
10,780 
9,880 
10,363 
9,762 

2,816,900 

0.091 

1,831 

1,941,700 
1,834,900 
2,439,000 

0.333 
0.300 
0.227 

1,204 
1,150 
1,242 

.00000567 
.00000577 
.00000517 
.00000500 
.00000320 

.00000578 

Olympia  sandstone  (Oregon). 
Chuckanut  sandstone  (Wash.) 
Dyckerhoif  Portland  cement, 
neat 

.... 

12,665 
11,389 

1,352 

*  See  Art.  5,  p.  5. 

436.  Resistance  to  Abrasion. — When  a  stone  is  strong  and  tough  enough 
to  resist  the  chipping  action  of  the  iron  horseshoes  and  wagon-tires  upon  it 
when  used  as  a  paving  material,  and  Avhen  it  weathers  perfectly,  its  life  is 
measured  by  its  resistance  to  the  abrading  action  of  the  traffic.  Prof. 
Bauschinger  very  fully  investigated  this  subject,  and  his  results  are  recorded 
in  volume  xi  of  his  Communications  (1884).  We  here  find  some  900  tests  of 
paving  materials,  most  of  which  are  summarized  by  averages  in  Table  XLIII. 
His  apparatus  is  shown  in  Fig.  585,  which  is  modelled  after  a  similar  machine 
shown  at  the  world's  fair  held  in  Paris  in  1878.  The  cut  as  here  shown  is 
to  a  scale  of  one-half  inch  to  the  foot,  so  that  the  diameter  of  the  revolving 
table  was  about  five  feet.  Any  given  specimen  was  held  to  a  fixed  position 


646 


THE  MATERIALS  OF  CONSTRUCTION'. 


on  the  plate,  two  specimens  being  tested  at  one  time.  The  specimens  wer 
all  dressed  to  4  inches  (10  cm.)  square,  and  they  were  weighted  with  30  kilc 
grams,  or  about  4  Ibs.,  per  square  inch.  Tests  were  made  both  with  an< 


3S0 


300 


2S0 


£000 


FIG.  580.— Compression  Tests  ou  Four  Kinds  of  English  Dolomite.     (Inst.  Civ.  Engrs., 

vol.  cvn.) 


FIG.  681.— Compression  Tests  on  Three  Kinds  of  Oolitic  Limestone.     (Inst.  Civ.  Engrs., 

vol.  cvii.) 

without  the  use  of  water,  but  mostly  without,  as  shown  in  the  table      Fine 

ery  (No.  3)  was  fed  to  the  plate  by  hand  at  the  rate  of  20  grams  for  every 

^volutions,  the  old  emery  being  at  the  same  time  brushed  off.     Two 

attendants  constantly  kept  the  emery  in  the  path  of  the  specimen.     The 


RESULTS  OF  TESTS  ON  STONE  AND  BRTCK. 


647 


fffl 


P  f) 


7  T 


7 


.000^5 


.00/0 


FIG.  582. — Compression   Tests    on    Three   Kinds    of  English   Sandstone.     (List.   Civ. 

Engrs.,  vol.  cvn.) 


FIG.  583.— Elastic  Properties  of  Various  Stones  under  Compressive  Stress.     (Wat.  Ars- 

Rep.  1894.) 


648 


THE  MATERIALS  OF  CONSTRUCTION. 


speed  was  20  revolutions  per  minute,  and  200  revolutions  completed  a  test, 
so  that  the  test  lasted  but  10  min.  The  different  specimens  were  set  at 
different  distances  from  the  centre,  so  as  to  wear  the  cast-iron  table  evenly, 
and  the  results  were  all  reduced  to  a  standard  radius  (distance  from  the 
centre)  of  49  cm.  (19.5  in.).  Elaborate  preliminary  studies  were  made  to 


0 

0  .(M 

FIG.  584. — Elastic  Properties  of  Various  Stones  under  Compressive  Stress. 

Rep.  1894.) 


(Wat.  ATS. 


determine  the  best  rate  of  feeding  emery,  best  size  of  grain,  best  weighting 
of  specimen,  and  the  law  of  wear  as  the  distance  out  from  the  centre 
varied.  Some  of  the  results  of  these  preliminary  tests  are  shown  in 
Figs.  580  and  587.  The  average  results  as  recorded  in  Table  XLIII 
indicate: 

1.  That  the  wet  grinding  was  about  twice  as  effective  as  the  dry  grinding, 
the  exact  average  ratios  being  given  in  the  last  column  of  the  table  for  each 
species  of  stone.* 

2.  There  is  no  fixed  relation  between  crushing  strength  and  abrasive 
resistance. 

3.  The  limestones  wear  about  five  times  and  the  sandstones  about  four 
times  as  fast  as  the  granites,  porphyries,  and  basalts. 

*  These  ratios  have  been  taken  out  from  the  wet  and  dry  tests  on  identical  material, 
nnd  therefore  are  not  the  ratios  of  the  two  general  average  results  in  the  previous 
column. 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


649 


FIG.  585.— Bauschinger's  Apparatus  for  Determining  Resistance  to  4-brasion  of  Paving 

Material. 


200  300  400  5W  600 

FIG.  586.— Showing  the  Relation  between   the  Abrasion,  Pressure,  and  Energy  used. 

(Btuischinger.) 


650 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE   XLIIL— AVERAGE    RESULTS   OF   BAUSCIIINGER'S   ABRASION   TESTS   OJ? 

PAVIXG    MATERIAL. 
(Communications,  vol.  xi,  1884.) 

Four-inch  cubes  of  the  material  were  pressed  on  an  iron  plate  with  a  weight  of  four 
pounds  per  square  inch,  and  20  grams  of  emery  fed  every  10  revolutions.  Results 
obtained  for  200  revolutions  at  a  radius  of  19.5  inches. 


Kind  of  Material. 

Average 
Specific 
Gravity. 

A  verage 
Weight 
per  Cubic 
Foot  in 
Pounds. 

Average 
Com- 
pressive 
Strength 
n  Pounds 
per 
Square 
Inch. 

Num- 
ber of 
Results 
Aver- 
aged. 

How 
ground: 
Dry  or 
Wet. 

Average 
Loss  of 
Volume 
in  Cubic 
Inches. 

Ratio: 

Loss  wet 

Loss  dry* 

j-1.72 
•1.90 

1.90 

1  1.78 
U.31 

\2M 

1  1.60 
[2.25 
^•2.50 
|3.20 
Is.  68 

2 
2 

2 
2 

2 

3 

2 
2 

2 
2 
2 

63 

27 

87 
82 
57 

01 

61 
63 

72 
61 

87 

48 
98 
36 
33 

164 
142 

180 
176 
161 

188 

163 
165 

170 
163 

180 

loo 

187 
148 
146 

22,400 
18,780 

26,200 
21,900 
24,500 

34,200 

23,000 
17,500 

26,000 
22,600 
20,500 

17,600 

j    92 

j    18 
)      2 
2 
(    93 
8 
j    86 

4 
9 

j      8 

j           p 

10 
f  163 
}    32 
j    44 
'(    38 
f  105 
'1    34 
(    20 
I      4 

J 

(      ^ 

dry 
wet 
dry 
wet 
dry 
wet 
dry 
dry 
wet 
dry 
wet 
dry 
wet 
dry 
wet 
dry 
dry 
wet 
dry 
wet 
dry 
wet 
dry 
wet 
dry 
wet 

0.24 

0.46 
0.28 
0.82 
0.27 
0.68 
0.19 
0.20 
0.24 
0.19 
0.47 
0.21 
0.19 
0.16 
0.35 
0.20 
1.10 
1.41 
0.81 
0.64 
0.38 
0.75 
0.51 

o!ei 

1.62 

Basalt     

Gneiss  

Quartz         

Olay-slate              •     .         .  . 

Breccia                ......    .  .    . 

Sandstone..         

2 
2 
2 
2 

Brick  and  tile 

Artificial  stone  ma 
Portland  cemeii 

Asphalt  paving.  .  . 

de  with  ) 

) 

0.20 

\ 
J6 

./£ 

gj 

x^> 

^ 

^ 

pffi- 

^p 

|^ 

j 

eft 

(jk 

^ 

>^ 

s* 
(tf£ 

$>* 

^1 

> 

tj 

^M 

rnflf 

^ 

^> 

1^ 

A 

^ 

T!JP 

^ 

r^ 

w^ 

^ 

C!iL-< 

^ 

Ingt 

U^^' 

FJ§ 

1 

^ 

/n  f  i 

T& 

t~~~' 

^ 

t^- 

^> 

>  — 

^ 

14§ 

'£tf? 

tff£ 

^//r7/ 

'(/Si 

-on 

WA 

VSt 

^/ 

Wfi 

"j. 

/<?  20  30 

FIG.  587. — Showing  the  Relation  between  the  Abrasion,  the  Emery  used,  and  the 
Pressure  exerted.     (Bauschinger.) 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


651 


4.  The  clay-slate  shows  the  best  results  in  abrasion,  but  only  a  few  speci- 
mens were  tested. 

5.  The  brick  and  tile  wear  about  twice  as  fast  and  the  cement  composi- 
tions about  three  times  as  fast  as  the  primitive  rocks. 

G.  The  resistance  of  asphalt  paving  to  abrasion  falls  between  the  cement 
mixtures  and  sandstone. 


FIG.  588. 


FIG.  589. 


FIG.  588. — Elastic  Properties  of  Common  Brick  used  in  Pier  Tests.  The  average  crush- 
ing strength  of  these  three  grades  of  brick,  crushed  endwise,  was  14,000,  10,500, 
and  7500  Ibs.  per  square  inch  respectively.  ( Wat.  Ars.  Rep.  1885,  p.  1138.) 

FIG.  589.— Showing  Method  of  Failure  of  Brick  Piers.     (Wat.  Ars.  Rep.  1883.) 


BKICK. 

437.  The  Strength  and  Elastic  Properties  of  single  bricK  are  of  relatively 
small  importance  unless  the  mortar  bond  has  nearly  as  great  strength.  As 
this  is  never  the  case  except  a  rich  Portland-cement  mortar  be  used,  it 
follows  that  in  ordinary  brick  masonry  the  strength  and  rigidity  of  the  brick 
used  is  of  small  importance  provided  any  reasonably  firm  brick  be  employed. 
Thus  in  Fig.  588  we  have  three  stress-diagrams  of  compression  tests  of  single 
brick,  showing  moduli  of  elasticity  from  2,000,000  to  4,000,000,  and  an 


652 


THE  MATERIALS  OF  CONSTRUCTION. 


RESULTS  OF  TESTS   ON  STONE  AND  BRICK. 


653 


ultimate  crushing  strength  from  8,000  to  14,000  Ibs.  per  square  inch.  In 
Fig.  590  are  shown  the  stress-diagrams  of  tests  on  columns  from  G  to  10  feet 
high  built  from  the  strongest  of  the  brick  tested  in  Fig.  588,  but  with 


JL 


0  /-Off  2-00  3.00 

FIG.  591.— Strength  of  Columns  of  Single  Hard-burned  Eastern  Face-brick  laid  flatwise 
one  upon  another  with  Plaster-of-paris  Joints.  Each  result  the  mean  of  two  tests. 
(Rep.  Wat.  Ars.  1894,  p.  440.) 


T'E 


6  A 


ST 


ff 


/  i?  /V 


FIG.  592.— Strength  of  Brick  Piers  with  Roseudale-cement-mortar  Joints,  1  C.  :  2  S. 

(Wat.  Ars.  Rep.  1883.) 

various  kinds  of  mortar.  When  lime-mortar  (1  lime  to  3  sand)  was  used 
at  ages  from  18  months  to  2  years,  the  modulus  of  elasticity  for  the  column 
as  a  whole  varied  for  the  first  loads  from  250,000  to  750,000,  and  the  ulti- 
mate strength  from  750  to  1300  Ibs.  per  square  inch.  The  method  of  failure 


654 


THE  MATERIALS  OF  CONSTRUCTION. 


of  all  these  columns  is  fairly  indicated  in  Fig.  589.  They  always  split 
longitudinally  and  spread  apart,  thus  showing  that  the  tensile  strength  of 
the  brick  is  really  a  very  important  quality. 


c  2 


=2- 


V* 


V0 


—H 


K 


When  Eosendale  (natural)  cement  mortar  (1  C.  :  2  S.)  was  used  the 
modulus  of  elasticity  was  raised  to  about  2,000,000,  and  the  ultimate  strength 
to  2000  Ibs.  per  square  inch. 

"When  Portland-cement  mortar  (1  C.  :  2  S.)  was  used  the  modulus  of 
elasticity  of  the  column  was  raised  3,000,000,  and  the  strength  to  2500  Ibs. 
per  square  inch. 

The  effect  of  adding  one  part  of  Rosendale  or  of  Portland  cement  to  two 
parts  of  lime  and  three  parts  of  sand  is  shown  by  two  diagrams  on  Fig.  590. 


RESULTS  OF  TESTS  OF  STONE  AND  BRICK. 


655 


S   ^1 


10 


"  ffff  £Q / V 


^ 


\ 


656 


THE  MATERIALS  OF  CONSTRUCTION. 


,& 


& 


m 


% 


I' 


/'  ft  o  o  awr/ 


A/  A  r 


6    6 


/ 


595. — Strength  of  Coinmou-brick   Piers  with    Rosendale-cement-mortar    Joints, 
1  C.  :  2  S.     (Wat.  Ars.  Rep.  1883.) 


soo 


A 


4- 


s«fr- 


ff  0 


A 


TV 


7  /V 


0     .001   .002  .003     0     .00/   .002  .003    0     ,00/   .002  .003    0     .0#/   .002  .003  .004 .006 
FIG.   596.— Strength    of  Common-brick  Piers  with  Roseudale-cement-mortar   Joints, 
1  C.  :  2  S.     ( Wat.  Ars.  Rep.  1883.) 


RESULTS  OF  TESTS   OF  STONE  AND  BRICK. 


657 


^  :1 


<o 


f 


p£fl 


y  .002  .002   0  .00/ 

!FiG.   597.— Strength  of  Common-brick  Piers   with    Roseudale-cement-mortar    Joints, 
1  C. :  2  S.     (Wat.  Ars.  Rep.  1883.) 


FIG.  598.  —  Strength  of  Face-brick  Piers  with  Portland-cement-  and  Lime-mortar  Joints. 

(Wat.  Ars.  Rep.  1883.) 


658 


THE  MATERIALS  OF  CONSTRUCTION. 


The  ultimate  strength  is  raised  to  1650  Ibs.  with  the  Kosendale,  and  to  1450 
Ibs.  per  square  inch  when  using  the  Portland  cement,  while  the  modulus  of 
elasticity  is  also  greatly  increased,  especially  under  the  higher  loads. 


I I 


The  effect  of  height,  as  related  to  breadth,  on  the  crushing  strength  of 
brick  is  shown  in  Fig.  591,  where  results  are  given  for  bricks  crushed  flat- 
wise in  columns  of  one,  two,  three,  four,  and  five  bricks  high,  with  plaster- 
of-paris  beds.  This  curve  is  quite  similar  to  that  in  Fig.  17,  p.  32. 

The  remaining  diagrams,  given  in  Figs.  592  to  COO,  showing  the  strength 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


659 


of  brick  columns  are  thought  to  be  self-explanatory  and  therefore  need  no 
further  comment  here.  The  original  publications,  furthermore,  are  generally 
accessible  in  this  country. 


i 

*~. 
fi> 

cf5 


- 


\ 


V 


Table  XLIV  contains  a  record  of  tests  on  some  of  the  best  building 
brick,  as  made  by  the  hydraulic  dry-press  method,  the  tests  in  crushing 
having  been  made  upon  the  bricks  flatwise.  This  gives  results  about  25  per 
cent  greater  than  if  the  tests  were  made  on  cubical  forms,  and  40  per  cent 
greater  than  if  the  brick  had  been  crushed  edgewise,  as  was  the  case  with 
the  v>aviner-brick  tests  on  which  are  recorded  in  Table  XLV. 


paving- 


660 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE    XLIV. — COMPARISON   OF   TRANSVERSE   AND    CRUSHING   TESTS 

OF    BRICK. 
(From  Watertowu  Arsenal  Tests  for  1894.) 


Modulus  of 

Trans- 
verse 
Test 
No. 

Kind  of  Brick. 

Rupture  in 
Transverse 
Tests, 
Pounds  per 
Square  Inch. 
3  Wl 

Mean  Crushing 
Strength  Flat 
wise, 
Pounds  pet- 
Square  Inch. 

Ratio  : 
Crushing 

Transverse' 

212 
213 
214 

215 

i 

From 
Hydraulic  Pressed  Brick  Co.,  St.  Louis 

754 
833 

829 

868 

10,350 

17,698 

8,495 
10,483 

13.8 
21.2 
10.2 
12.1 

216 

604 

5,573 

9.2 

223 

From 

455 

5,596 

12.3 

224 

Hydraulic  Pressed  Brick  Co.,  Chicago 

308 

3,271 

10.6 

226 

From 
Hydraulic  Pressed  Brick  Co.,  Omaha 

1,244 

13,506 

10.9 

From 

225 

Northern  Hydraulic  Pressed  Brick  Co., 

455 

6,583 

14.4 

Minneapolis 

206 

936 

12,823 

13.7 

207 
208 
209 
210 

From 
Eastern  Hydraulic  Pressed  Brick  Co., 
Philadelphia 

1,232 

1,066 
756 
1,038 

13,052 
15,633 
12,196 
12,445 

10.6 
14.6 
16.1 
11.9 

211 

974 

12,866 

13.2 

217 

785 

8,848 

11.3 

218 

1,043 

11,867 

11.4 

219 
220 
221 

rom 
Philadelphia  and  Boston  Face-brick  Co., 
Boston 

741 
568 

858 

7,778 
3,093 
8,217 

10.5 
5.4 
9.6 

222 

358 

2,686 

7.5 

438.  Results  of  Tests  of  Paving-brick.— Table  XLV  contains  the  results 
of  tests  made  by  the  author  on  paving-brick  in  accordance  with  the  methods 
he  has  established  and  described  in  Chap.  XXII.  The  brick  intended  for 
the  cross-breaking  and  for  the  crushing  tests  are  ground  first  on  one  flat  side 
to  obtain  a  true  plane  of  reference,  and  then  on  the  opposite  edges  to  true 
parallel  planes.  This  grinding  is  done  for  him  at  a.  regular  stone  (marble) 
works,  and  there  seems  to  be  little  difficulty  in  obtaining  satisfactory 
results.  The  knife-edge  bearings  used  in  the  cross-breaking  tests  are  some- 
what rounded,  but  are  not  cushioned. 

The  ends  of  brick  which  have  been  broken  across  are  then  used  for  the 
crushing  test.  The  crushing  force  is  applied  edgewise,  using  ordinary  tar- 
board  as  a  cushioning  material.  Plain  steel  surfaces  are  better  if  they  are 
perfectly  true.  One  of  the  bearings  should  be  adjustable  or  have  a  ball-and- 
socket  support.  The  specimen  must  also  be  placed  exactly  in  the  axis  of  the 


RESULTS  OF  TESTS  ON  STONE  AND  BRICK. 


661 


TABLE    XLV. — TESTS   OF   PAVIXG-BRICK   MADE   BY   THE   AUTHOR. 
(Private  Records.) 


Modulus  of 

Impact  Test.    (See  Art.  337,  p.  457.) 

Mark. 

Number  of 
Tests 
Averaged. 

Rupture  in 
Cross-breaking 
Edgewise  in 
Pounds  per 
Square  Inch. 
.      Swl 
*  ~  2&/<3  ' 

Crushing 
Strength 
Edgewise  in 
Pounds  per 
Square  Inch. 

t 

Absorption 
Test. 
Percentage 
of  Water 
by  Weight. 

Loss  of 
Weight  of 
Brick, 
Per  Cent. 

Loss  of 
Weight  of 
Granite 
Blocks, 
Per  Cent. 

Ratio: 
Loss  of  brick 

Loss  of  granite 

A 

12 

1,369 

4,885 

9.84 

2.34 

4.2 

5.32 

B 

5 

1,495 

4,974 

13.82 

2.78 

4.97 

4.1 

C 

6 

2.808 

9,890 

12,15 

2.5 

4.85 

0.64 

D 

3 

3,032 

16,140 

16.42 

3.6 

4.56 

1.36 

E 

4 

2,620 

12,330 

13.98 

3.6 

3.88 

3.40 

F 

3 

2,734 

15,155 

14.34 

3.6 

3.98 

1.12 

G 

3 

2,335 

12,040 

26.54 

3.6 

7.37 

0.87 

H 

3 

2,335 

17,500 

19.17 

3.6 

5.32 

0.64 

I 

3 

2,825 

17,480 

11.04 

3.6 

3.07 

1.12 

J 

3 

2,100 

13,150 

18.38 

3.6 

5.11 

0.33 

K 

5 

2,570 

20,420 

26.67 

3.38 

7.89 

0.55 

L 

5 

2,152 

15,530 

13.0 

3.2 

4.06 

2.20 

M 

18 

2,401 

13,366 

15.7 

1.8 

8.7 

0.79 

N 

6 

2,635 

15,360 

163 

4.1 

4.0 

2.79 

O 

6 

2,208 

13,300 

15.3 

5.0 

3.1 

2.92 

P 

5 

2,674 

16,830 

8.65 

2.45 

3.55 

1.29 

Q 

6 

2,320 

14,420 

14.53 

3.41 

4.26 

0.67 

R 

4 

3,110 

20,802 

19.5 

2.5 

7.8 

0.5 

s 

4 

1,780 

11,037 

13.48 

3.03 

4.45 

6.61 

T 

5 

2,930 

13,260 

11.37 

3.89 

2.92 

3.03 

U 

3 

2,570 

10,400 

15.1 

2.21 

6.83 

2.2 

V 

5 

2,640 

7,830 

34.1 

2.21 

15.4 

1.1 

machine.  Failure  should  come  suddenly  with  a  loud  report,  with  little  or 
no  previous  spalling  of  the  specimen. 

The  impact  tests  were  made  in  a  tumbler,  or  rattler,  made  up  by  lining 
an  oil-barrel  with  steel  strips  and  mounting  it  on  trunnions.  Standard 
Missouri  granite  blocks,  rectangular  in  form,  and  weighing  about  the  same 
as  a  paving-brick  (6  Ibs.)  are  obtained  in  quantities,  specially  prepared  for 
these  tests.  There  were  always  five  of  these,  freshly  cut  (not  sawed),  put  in 
the  rattler  along  with  the  brick,  and  the  rattler  run  at  30  to  40  revolutions 
per  minute  for  15  to  30  minutes.  The  loss  in  weight  of  the  brick  is  then 
found  as  compared  with  the  loss  in  weight  of  the  granite  blocks.  It  has 
been  customary  to  add  from  5  to  10  cast-iron  bricks,  having  rounded  edges, 
specially  cast  for  the  purpose,  these  also  weighing  6  pounds  each.  Evidently 
such  a  test  is  i  n  no  sense  an  abrasion  test,  but  strictly  a  test  for  shock  resist- 
ance, or  for  resistance  to  impact. 

The  absorption  test  has  been  made  by  drying  24  hours  on  top  of  boilers 
and  then  soaking  24  hours.  While  these  intervals  are  not  long  enough  to 
give  absolute  results,  they  serve  very  well  for  commercial  purposes.  The 
bricks  which  have  been  through  the  rattler  are  used  for  this  test,  as  their 
glazed  surfaces  are  then  largely  removed. 


662 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE   XLYI. — TESTS   OF    BUILDING-BRICK    AT   THE 
WATERTOWN  ARSENAL. 

(Rep.  1894.) 


• 

Description  of  Brick. 

Compression 

Test. 

Cross- 
breaking 
Strength 
in  Pounds 
per 
Square 
Inch. 

3    Wl 
*~2'  bh* 

Shearing 
Strength 
in  Pounds 
per 
Square 
Inch. 

Percentage 
of  Absorption 

Direction 
of 
Loading. 

Crushing 
Strength 
in  Pounds 
per 
Square 
Inch. 

By 
Weight. 

3y 

Volume. 

HYDRAULIC  PRESS  BRICK  Co. 
—  ST.  Louis,  Mo. 

Medium  red                      ... 

Flatwise 

Edgewise 
Flatwise 

>  < 

« 
ti 

Flatwise 

VI 

Edgewise 
Flatwise 

Flatwise 

Flatwise 

Flatwise 

5,266 

10,284 
17,558 
5,992 
10,648 
17,023 
8,815 
8,620 

11,432 
8,907 

6,388 

8,144 
8,861 

3,779 
5,589 
5,192 

13,511 
12,907 
13,506 

7,509 
6,814 

20,616 
10,950 

18,574 

9,686 
12,372 
11,201 

'754 

'833 
829 

868 
604 

308 
455 

1244 
455 

ioii 

642 

1047 

'784 
'714 

18.0 

10.1 
10.1 

8.0 

9.6 
15.4 

14.6 
14.8 

11.4 

14.8 

7.6 
9.1 
6.0 

31.5 

20.0 
20.0 

16.1 

19.0 

28.1 

27.7 
27.9 

22.2 

27.4 

14.6 
17.6 
12.6 

Dark  red       

Paving  stock 

Paving  slock                   

No  6  stock   dark  red  

No.  10  stock,  dark  red   
No.  500  stock,  buff,  speckled  .  . 
No.  503  stock,  light  chocolate.  . 
No.  504  stock,  light  choco   \ 
late  with  dark  speckles      j  '  ' 
No.  509  stock,  dark  buff  ) 
with  darker  speckles       J 
No.  510  stock,  buff  with  ) 
dark  speckles                  j-  •  •  •  • 
No.  511  stock,  light  buff  
Brow  11 

CHICAGO     HYDRAULIC     PRESS 
BRICK  Co.  —  CHICAGO,  ILL. 

Brown     

Red  

Red  

OMAHA      HYDRAULIC      PRESS 
BRICK  Co.  —  OMAHA,  NEB. 

Shade  No.  5  

Shade  No.  7  

Shade  No.  6  

NORTHERN  HYDRAULIC  PRESS 
BRICK    Co.  —  MINNEAPOLIS, 
MINN. 

Dark  red  

Dark  red   

BROOKE    TERRACOTTA    Co.— 
LAZEARVILLE,  W.  VA. 

No.  4,  dark  buff  

No.  5,  medium  dnrk  buff  .  .  . 
No.  10,  light  buff  

FINDLAY    HYDRAULIC      PRESS 
BRICK  Co.—  FINDLAY,  OHIO. 

No.  12,  dark  red  

No.  18,  dark  red  

No.  14,  dark  red  

RESULTS  OF  TESTS  ON  STONE  AND  BRICK.  663 

TESTS    OF   BUILDING-BRICK   AT   THE   WATERTOWN   ARSENAL — Continued. 


Description  of  Brick. 

Compression 
Test. 

Cross- 
breaking 
Strength 
in  Pounds 
per 
Square 
Inch. 

3    Wl 
f~9'  6/i2 

Shearing 
Strength 
in  Pounds 
per 
Square 
Inch. 

Percentage 
of  Absorption 

Direction 
of 
Loading. 

Crushing 
Strength 
in  Pounds 
per 
Square 
Inch. 

By 

Weight. 

By 
Volume. 

EASTERN    HYDRAULIC     PRESS 
BRICK    Co.  —  PHILADELPHIA, 
PA. 

Shade  200  li^ht  buff  color. 

Flatwise 

Edgewise 
Flatwise 

Edgewise 
Flatwise 

Edgewise 
Flatwise 

Flatwise 

Edgewise 
Flatwise 

Edgewise 
Flatwise 

Edgewise 
Flatwise 

15,285 
13,292 

9,319 
15,374 
12,671 
9,273 
13,059 
15,081 
9,945 
12,866 

3,896 

8,487 
5,877 
10,942 
7,774 
17,023 
3,161 
8,946 
4,756 
3,070 

936 
1232 

1066 
756 

1038 
'974 

'785 

1043 
741 

568 
858 

358 

1767 
1097 

988 
536 

6.9 

5.5 
7.9 

7.1 
5.5 

19.0 
11.0 

10.0 
18.1 
15.2 

14.5 

11.6 
16.1 

14.5 
11.5 

32.6 
21.6 

20.1 
31.0 
27.1 

Shade  210,  slightly  darker  \ 
thau  shade  200                     f  " 
Shade  210     

Shade  220   buff  

Shade  300  buff  darker 

Shade  300      , 

Shade  390  gray  

Shade  410  light  chocolate  .... 

Shade  410  

Shade  400  

PHILADELPHIA    AND     BOSTON 
FACE-BRICK    Co.  —  BOSTON, 

MASS. 

Salmon  color  

Light  red 

Light  red             ... 

Dark  red  

Chocolate-brown 

Chocolate-brown        .... 

Creain  color      

Buff 

Buff    

Gray  

In  Table  XLVI  are  given  the  more  significant  results  of  a  very  careful 
series  of  tests  on  building  brick,  these  being  a  part  of  an  elaborate  series  of 
tests  on  building  materials  begun  in  1894,  and  still  in  progress.  These 
brick  are  supposed  to  represent  the  better  grades  of  building  brick  on  the 
market  in  different  parts  of  this  country.  The  compression  tests  were  made 
by  bedding  the  pressed  surfaces  in  plaster  of  Paris.  A  great  difference 
will  be  observed  between  the  crushing  strength  flatwise  and  edgewise. 
The  strength  of  these  brick,  when  tested  singly,  should  be  compared  with 
the  strength  of  brick  piers,  with  various  mortars,  as  shown  in  Figs.  590  to 
600. 


CHAPTER  XXXII. 
EXPERIMENTAL  VALUES  OF  THE  STRENGTH   OF  TIMBER. 

439.    The   Mechanical   Tests   of  the   U.   S.    Timber   Investigations.— 

Although  timber  is  the  oldest  and  still  the  most  universally  used  of  all  struc- 
tural material,  no  rational  determination  of  the  laws  controlling-  the  strength 
of  timber  has  been  attempted  until  within  a  few  years.  Bauschinger  made 
a  few  experiments  in  1882,  and  pointed  the  way  to  a  thorough  study  of  tim- 
ber which  since  1890  has  been  conducted  by  the  II.  S.  Government.*  These 
investigations  are  still  incomplete,  but  they  already  furnish  a  vast  amount  of 
valuable  information,  a  part  of  which  has  been  published  in  bulletins  and 
circulars  issued  by  the  Forestry  Division  (Dr.  B.  E.  Fernow,  Chief)  of  the 
U.  S.  Agricultural  Department  from  time  to  time.  The  following  direct 
quotations  in  this  chapter  are  taken  from  Forestry  Circular  No.  15,  1897: 

"  The  superiority  of  the  data  obtained  in  these  investigations  lies  in  (1) 
the  correct  identification  of  the  material,  it  being  collected  by  a  competent 
botanist  in  the  woods;  (2)  selection  of  representative  trees  with  record  of 
age,  development,  place,  and  soil  where  grown,  etc. ;  (3)  determination  of 
moisture  conditions,  specific  gravity,  and  record  of  position  in  the  tree  of 
the  test-pieces;  (4)  large  number  of  trees  and  of  test-pieces  from  each  tree 
(see  Table  XLVII) ;  (5)  employment  of  large-  and  small-sized  test  material 
from  the  same  trees;  (G)  uniformity  of  method  for  an  unusually  large  num- 
ber of  tests. 

"  The  entire  work  of  the  mechanical  test  series  carried  on  through  nearly 
six  years  intermittently,  as  funds  were  available,  comprises  so  far  32  species 
with  300  test  trees,  furnishing  over  COOO  test-sticks  and  about  40,000  tests 
in  all.  f 

11  In  addition  to  the  material  for  mechanical  tests,  about  20,000  pieces  of 
material  for  physical  examination  from  780  trees  (including  the  300  trees. 
used  in  mechanical  tests)  have  been  collected  to  determine  structure,  char- 
acter of  growth,  specific  gravity  of  green  and  dry  wood,  shrinkage,  moisture 
conditions,  and  other  properties  and  behavior. 


*  For  a  short  general  description  of  these  investigations  see  Art.  340,  p.  462. 
f  These  tests  have  all  been  conducted  under  the  direction  of  the  author  in  his  labora- 
tory at  St.  Louis,  Mo. 

604 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER. 


TABLE   XLVII. — AN   ACCOUNT   OF   THE    MATERIAL   OPERATED   UPON 

(1891-1896)    IN   THE    U.   S.   TIMBER   INVESTIGATIONS. 

(From  U.  S.  Forestry  Circular,  No.  15.) 


00 

O> 

.2 

>v 

! 

05 

£ 

'81 

CM 

-~ 

Name  of  Species. 

o 

0 

U 

®E  ?*> 

Localities,  and  Number  of  Trees  from  Each. 

1 

1 

2 

g 

E 

a3  Q.<_ 

£ 

fe 

1 

3°°' 

1 

Long-leaf  piiie 

* 
68 

6478 

.61 

Alabama—  coast   plain  (22)*,  uplands   (6), 

(Pinus  palustris) 

•hill   district   (6)  ;     Georgia—  undulating 
uplands    (6)  ;     South    Carolina  —  coast 

plain   (7);   Mississippi  —  low   coast  plain 

(2);  Louisiana  —  low  coast  plain,  gravelly 

soil   (7).  sandy   loam   (6)  ;    Texas—  low- 

coast  plain  (6) 

2 

Cuban  pine 
(Pinus  heteropJiylla] 

12 

2113 

.63 

Alabama  —  coast    plain    (6);    Georgia  —  up- 
lands (1);  South  Carolina—  coast  (5) 

3 

Short-leaf  pine 

22 

1831 

.51 

Alabama  —  uplands    (4);     Missouri  —  low 

(Pinus  ecJiinata] 

hilly  uplands   (6);   Arkansas  —  low  hilly 

4 

Loblolly-pine 

32 

3335 

.53 

uplands  (6);  Texas—  uplands  (6) 
Alabama  —  mountainous    plateau   (8),  low 

(Pinus  tceda) 

coast   plain   (6)  ;     Arkansas—  level  flood 

plain  (5);  Georgia—  level  coast  plain  (6); 

South  Carolina  —  low  coast  plain  (7) 

5 

White  pine 

17 

540 

.38 

Wisconsin  —  clay  uplands  (5),  sandy  soils 

(Pinus  strobus) 

(4),    sandy   loam    (5)  ;    Michigan—  level 

drift-lands  (3) 

C 

Red      pine      (Norway 

8 

412 

.50 

Wisconsin—  drift  (5);  Michigan—  (3) 

pine) 

• 

(Pinus  resi?iosa) 

7 

Spruce-pine 

4 

696 

.44 

Alabama  —  low  coast  plain 

(Pinus  glabra) 

8 

Bald  cypress 
(  Taxadium  disticJium) 

20 

3396 

.46 

South  Carolina—  pine-barren  (6),  river-bot- 
tom (4);   Louisiana  —  coast  plain,  border 

of  lake  (4);  Mississippi  —  Yazoo  bottom 

(3),  upland  (3) 

9 

White  cedar 

4 

354 

.37 

Mississippi  —  low  plain  (4) 

(  GhamfKcyparu  thyoides} 

10 

Douglas  spruce 

225 

.51 

(Oregon  fir) 

* 

(Pseudotsuga  taxifolia) 

(douglasii) 

11 

White  oak 

12 

1009 

.80 

Alabama  —  ridges  of  Tennessee  Valley  (5); 

(Quercus  alba) 

Mississippi—  low  plain  (7) 

12 

Overcup-oak 

10 

911 

.74 

Mississippi  —  low   plain   (7)  ;    Arkansas  — 

(  Quercus  lyrata) 

Mississippi  bottoms  (8) 

18 

Post-oak 

8 

256 

.80 

Alabama  —  Tennessee  Valley  (5);  Arkansas 

14 

(Quercus  minor] 
Cow-oak 

11 

935 

.74 

—  Mississippi  bottom  (3) 
Alabama  —  Tennessee  Valley  (4);  Arkansas 

(Quercus  michauxii] 

—  Mississippi  bottoms  (3);  Mississippi  — 

low  plain  (4) 

*  Sixteen  of  these  were  bled  trees,  to  study  the  effects  of  boxing, 
f  The  specific  gravity  here  presented  is,  for  all  but  8  of  the  conifers,  that  of  the  test- 
pieces  only,  and  is  not  an  average  for  the  material  on  the  whole. 


QQQ  THE  MATERIALS  OF  CONSTRUCTION. 

AN  ACCOUNT   OF   THE   U.  S.    TIMBER   INVESTIGATIONS — continued. 


1 

% 

t/3 

'>  -o 

EH 

i 

II 

1 

Name  of  Species. 

1 

o 

ife 

Localities,  and  Number  of  Trees  fron  Each. 

s 

3 

£ 

3 

g 

|^S 

15 

Red  oak 

5 

299 

.73 

Alabama  —  Tennessee  Valley  (5) 

16 

(Quercus  rubra) 
Texan  oak 

5 

479 

.73 

Arkansas—  Mississippi  bottom  (2);  Missis- 

(Southern red  oak) 

^ 

sippi  —  low  plain  (3) 

(Quercus  te.rana) 

17 

Yellow  oak  (black) 

5 

222 

.72 

Alabama  —  Tennessee  Valley  (5) 

(Quercus  velutina) 

18 

Water-oak  (aguatica) 

4 

132 

.73 

Mississippi  —  low  plain  (4) 

(Quercus  nigra) 

19 

Willow-oak 

12 

649 

.72 

Alabama5—  Tennessee  Valley  (5);  Arkansas 

(Quercus  phellos) 

—Mississippi  bottom  (3)  ;    Mississippi  — 

low  plain  (4) 

20 

Spanish  oak 

11 

1035 

.73 

Alabama—  Tennessee  Valley  (5);  Arkansas 

(Quercus  digitata) 

—  Mississippi   bottom    (3);    Mississippi  — 

low  plain  (3) 

21 

Shanbark     (shellbark) 

6 

794 

.81 

Mississippi—  alluvial  plain  (3),  limestone  (3) 

hickory 

(Ilicoria  ovata) 

22 

Vlockernut  hickory 

4 

300 

.85 

1 

(white)  (Hicorin  alba] 

23 

Water-hickory 

2 

197 

.73 

(Hicoi'ia  aquatica) 

24 

Bittern  ut  hickory 

4 

100 

.77 

(Hicoria  minima] 

-Mississippi  —  low  plain 

25 

Nutmeg-hickory 

3 

294 

,78 

(Hicoria  myristicae- 

formis) 

26 

Peca  n    (  Ilicoria  peca  n  ) 

2 

172 

.78 

27 

Pignut  hickory 

3 

84 

.80 

(Hicoria  glabra) 

28 

White  elm 

2 

91 

.54 

Mississippi  bottom 

(  Ulmus  americana) 

29 

Cedar  elm 

3 

201 

.74 

Arkansas  bottom 

(  Ulmus  crassifolia 

30 

White  ash 

3 

476 

.62 

Mississippi  bottom 

(Fraxinus  americana) 

31 

Green  ash  (mridis) 

1 

45 

.62 

Mississippi  bottom 

(Fraxinus  lanceolata 

32 

Sweet-gum 
(Liouidambar  slyra 

7 

508 

.59 

Arkansas  —  bottom    (3)  ;    Mississippi—  low 
plain  (4) 

ciflua 

*  The  specific  gravity  here  presented  is,  for  all  but  8  of  the  conifers,  that  of  the  test- 
pieces  only,  and  is  not  an  average  for  the  material  on  the  whole. 

440.  The  Investigations  still  in  Progress, — "  As  will  be  observed,  some 
species,  notably  the  Southern  pines,  have  been  more  fully  investigated,  and 
the  results  on  these  (which  have  been  published  in  more  detail  in  Circular 
No.  12)  may  be  taken  as  authoritative.  With  those  species  of  which  only  a, 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.     667 

small  number  of  trees  have  been  tested,  this  can  be  claimed  only  within 
limits  and  in  proportion  to  the  number  of  tests. 

"  The  great  variation  in  strength  which  is  noticeable  in  timber  of  the 
same  species  makes  it  necessary  to  accept  with  caution  the  result  of  a  limited 
number  of  tests  as  representing  the  average  for  the  species,  for  it  may  have 
happened  that  only  superior  or  only  inferior  material  has  come  to  test. 
Hence  we  would  not  be  entitled  to  conclude  that  pignut  hickory  is  14  per 
cent  stronger  than  shellbark,  as  it  would  appear  in  the  tables,  for  the  30 
test-sticks  of  the  former  may  easily  have  been  superior  material.  Only  a 
detail  examination  of  the  test-pieces  or  a  fuller  series  of  tests  would  enlighten 
us  as  to  the  comparative  value  of  the  results. 

"  The  following  data,  therefore,  are  not  to  be  considered  as  in  any  sense 
final  values  for  the  species  except  where  the  number  of  trees  and  tests  is  very 
large.  The  variation  in  strength,  as  will  be  seen  from  the  tables,  in  wood 
of  the  virgin  forest  is  in  some  species  so  great  that  by  proper  inspection  and 
selection  values  differing  by  25  to  50  per  cent  may  be  obtained  from  different 
parts  of  the  same  tree,  and  values  differing  100  to  200  per  cent  within  the 
same  species.  These  differences  have  all  their  definite  recognizable  causes, 
to  find  and  formulate  which  is  the  final  aim  of  these  investigations. 

"  The  tests  are  intentionally  not  made  on  selected  material  (except  to 
discard  absolutely  defective  pieces),  but  on  material  as  it  comes  from  the 
trees,  so  as  to  arrive  at  an  average  statement  for  the  species,  when  a  sufficient 
number  of  trees  has  been  tested.  How  urgent  is  the  need  for  data  of  inspec- 
tion as  above  indicated  will  appear  from  the  wide  range  of  results  recorded. 

"  To  enable  any  engineer  to  use  the  data  here  given  with  due  caution 
and  judgment,  not  only  the  ranges  of  values  and  the  average  of  all  values 
obtained,  but  also  the  proportion  of  tests  which  came  near  the  average  values 
has  been  stated,  as  well  as  the  average  result  of  the  highest  and  lowest  values 
of  10  per  cent  of  the  tests.  With  this  information  and  a  statement  of  the 
actual  number  of  tests  involved,  the  comparative  merit  of  the  stated  values 
can  be  judged.  With  a  large  n timber  of  tests,  to  be  sure,  it  is  more  likely 
that  an  average  value  of  the  species  has  been  found.  The  actual  test  results 
have  been  rounded  off  to  even  hundreds  in  the  tables." 

441.  The  Moisture  Factor  in  timber  was  described  in  Articles  192  and 
202.  It  has  been  determined  by  cutting  a  thin  disc  from  across  the  entire 
section  of  the  test-stick  near  the  place  of  failure  and  finding  its  weight  as 
first  taken  and  after  drying  at  220°  F.  In  the  following  tables  all  values 
have  been  reduced  to  a  standard  moisture  of  12  per  cent,*  which  may  be 
regarded  as  that  of  dry  timber  out  of  doors.  With  all  the  species  tested  the 
strength  at  12  per  cent  moisture  is  some  75  per  cent  stronger  than  the  same 

*  The  author  is  responsible  for  the  reduction  of  the  results  on  the  Southern  pines  from 
15  per  cent  to  12  per  cent  moisture  to  bring  them  into  harmony  with  the  other  test 
results.  The  former  was  used  as  the  standard  of  reference  at  first,  but  it  was  afterwards 
decided  this  was  too  high  for  well-seasoned  timber.  (See  Forestry  Circular  No.  12  for 
the  strength-moisture  curves  for  the  Southern  pines.) 


668 


THE  MATERIALS  OF  CONSTRUCTION. 


sticks  are  either  green  or  wlien  wet  through  after  seasoning.  In  fact,  it  has 
been  shown  that  water  reabsorbed  after  drying  (which  is  the  same  as 
seasoning)  has  the  same  weakening  effect  as  the  original  sap.  This  is 
manifest  from  Fig.  G01,  which  contains  the  results  of  a  series  of  tests  on 


40 


30 


20 


10 


I 


n\cff(/$> 


\ 


STRW&Th  IN  AW0& 


•fiWN. 


4,000        6flff0        $000        /0,000 

FIG.  601.— Showing  Variation  of  Strength  of  Short-leaf  Pine.  Sap-wood,  with  Varying 
Percentages  of  Moisture  both  for  Drying  and  for  lleabsorbing  Conditions.  Tests  by 
the  author.  Drying  conditions  marked  bv  a  0  :  reabsorbing  conditions  marked 
by  a  X. 

identical  material  tested  at  various  moisture  conditions  in  drying  out  to  a 
nearly  zero  moisture,  and  again  at  similar  moisture  conditions  when  moisture 
was  uniformly  reabsorbed. 

It  is  the  absence  of  any  determination  of  the  moisture  condition  of  the 
test  material  that  vitiates  practically  all  tests  of  the  strength  of  timber 
except  such  as  have  been  made  by  Bauschinger,  Tetmajer,  and  those  here 
under  consideration.  Since  large  timbers  require  many  years  to  season,  or 
dry,  in  the  open  air,  while  small  test  sticks  dry  out  very  quickly,  it  is  certain 
that  the  difference  in  the  moisture  conditions  will  fully  explain  the  marked 
differences  which  have  been  observed  in  the  strength  of  identical  material  in 
different  sizes.  It  is  to  be  hoped  that  in  future  all  tests  of  the  strength  of 
timber  will  be  so  made  as  to  fully  reveal  this  condition  as  a  definite  percent- 
age of  moisture  across  the  section  near  the  region  of  failure. 

In  all  the  tests  made  by  the  author,  practically  identical  strength  moduli 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.      669 


were  obtained  on  large  and  small  sizes  of  the  same  material  when  they  were 
all  reduced  to  the  same  moisture  condition  and  were  equally  free  from, 
defects.  Hence  tests  on  small  sizes  (3  to  4  inches  on  a  side)  will  give  reli- 
able factors  to  use  in  actual  practice. 

As  shown  in  Fig.  G02,  the  increase  of  strength  with  diminishing  moisture 


MM 


W 


tva 


400C 


A 


0  20          44  60  80  100 

FIG.  602.  —  Typical  Relation  between  Strength  and  Moisture  of  Timber.  This  diagram 
shows  the  relation  of  crushing  strength  parallel  to  the  grain  to  the  percentage  of 
moisture  for  one  species  of  oak.  (From  the  Author's  U.  S.  Timber-  Test  Records.) 

does  not  become  apparent  until  the  moisture  percentage  becomes  less  than 
about  40  per  cent  (and  if  it  were  quite  evenly  distributed  it  would  be  at 
about  33  per  cent).  For  a  greater  percentage  of  moisture  than  this  the  water 
fills  not  only  the  cell-walls  (see  Art.  194),  but  also  the  cell-cavities  or  lumina. 
Since  the  weakening  effect  comes  only  from  the  wetting  of  the  walls  them- 
selves, it  follows  that  after  they  are  fully  saturated  any  excess  of  water  which 
occupies  the  cell  lumina  would  be  inoperative.  Xo  increase  of  strength  is 
noticeable,  therefore,  until  the  cell-walls  themselves  (the  woody  fibre)  begin 
to  dry  out,  when  the  increase  of  strength  becomes  very  rapid.  If  this  drying 
action  could  occur  uniformly  across  the  entire  cross-section  of  the  specimen, 
the  locus  of  the  strength-moisture  relation  would  be  practically  two  straight 
lines,  one  quite  straight  and  parallel  to  the  moisture  axis,  and  the  second 
somewhat  convex  to  the  strength  axis,  and  intersecting  the  former  locus  at 
about  33  per  cent  moisture.  The  locus  becomes  a  continuous  curve  when 
the  outer  parts  dry  very  much  more  rapidly  than  the  inner  parts,  as  is  the 
case,  of  necessity,  in  all  processes  of  drying.  To  avoid  this  mixed  condition 
it  is  necessary  to  make  the  tests  on  material  absolutely  green  *  or  uniformly 


*  The  "  green  "  sticks  of  the  U.  S.  tests  were  placed,  after  sawing,  in  a  "wet  room," 
where  the  air  was  kept  at  the  point  of  saturation,  or  as  nearly  so  as  possible. 


670  THE  MATERIALS  OF  CONSTRUCTION. 

dry  (but  still  containing  from  10  to  15  per  cent  of  atmospheric  moisture). 
Timber  is  never  uniformly  half  dry. 

TABLE  XLVIII.— STRENGTH  OF  AMERICAN  TIMBER.  CONDENSED  RESULTS 
OF  THE  U.  S.  TIMBER  TESTS.  ALL  VALUES  REDUCED  TO  A  STAND- 
ARD MOISTURE  OF  12  PER  CENT  OF  THE  DRY  WEIGHT. 

'Compiled  from  the  tables  in  U.  S.  forestry  Circular,  No.  15.) 


Species. 

1 
1 

I 

68 
16 
°2 
32 
6 
3 
3 

14 
10 
5 
11 
6 
3 
5 
3 
12 
5 

6 
4 
2 
4 
3 
2 
3 

2 
3 

3 

1 

7 

1 

I 
> 

«j 

i      cc 
^ 

!       22 

"o 

i 

& 

Specific  Gravitj'. 

o 

Cross-bending  Tests. 

Crushing  Endwise. 

o 

1 

o 

p 

03 

3 

O 

a 

o 

1 
"3 

U) 

a 

1 
55 

1 

o 

S 
a 

5 

"Sc 

z 

.2 
1 

1 

'5 

1 

3 

o 
•» 

"3 

"3 

1.  Long-leaf  pine  
2.  Cuban          "    
3    Short-leaf    " 

1230 
410 
330 
660 
130 
100 
170 

655 

87 
41 

218 
216 
49 
256 
57 
117 
40 
31 
153 
251 

137 
75 
14 
25 
72 
37 
30 

18 
44 

87 
10 

118 

.61 
63 
.51 

'1 

.50 
.62 

.46 
.37 
.51 

.80 
.74 
.80 
.74 
.72 
.73 
72 
.73 
.72 
.73 

.81 
.85 
.73 

.77 
.78 
.78 
.89 

.54 
.74 

.62 
.62 

.59 

38 
39 
32 
33 
24 
31 
39 

29 
23 
32 

50 
46 
50 
46 
45 
46 
45 
46 
45 
46 

51 
53 
46 
48 
49 
49 
56 

34 
46 

39 
39 

37 

Ib.  sq.in. 

10,000 
11,100 
7,800 
9,200 
6,400 
7,700 
8,400 

6,600 
5,800 
6,400 

9,600 
7,500 
8,400 
7,600 
9,200 
9,400 
8,100 
8,800 
7,400 
8,600 

11,200 
11,700 
9,800 
11,100 
9,300 
11,600 
12,600 

7,300 

8,000 

7,900 
8,900 

7,800 

Ib.  sq.in. 

12,600 
13,600 
10,100 
11,300 
7,900 
9,100 
10,000 

7,900 
6,300 
7,900 

13,100 
11,300 
12,300 
11,500 
11,400 
13,100 
10,800 
12,400 
10,400 
12,000 

16,000 
15,200 
12,500 
15,000 
12,500 
15,300 
18,700 

10,300 
13,500 

10,800 
11,600 

9,500 

Ib.  sq.  in. 

2,070,000 
2,370,000 
1,680,000 
2,050,000 
1,390,000 
1,620,000 
1,640,000 

1,290,000 
910,000 
1,680,000 

2,090,000 
1,620,000 
2,030,000 
1,610,000 
,970,000 
1,860,000 
1,740,000 
2,000,000 
1,750,000 
1,930,000 

2,390,000 
2,320,000 
2,080,000 
2,280,000 
1,940,000 
2,530,000 
2,730,000 

1,540,000 
1,700,000 

1,640,000 
2,050,000 

1,700,000 

Ib.  sq.  in 

8,000 
8,700 
6,500 
7,400 
5,400 
6,700 
7,300 

6,000 
5,200 
5,700 

8,500 
7,300 
7,100 
7,400 
7,200 
8,100 
7,300 
7,800 
7,200 
7,700 

9,500 
10,100 
8,400 
9,600 
8,800 
9,100 
10,900 

6,500 
8,000 

7,200 
8,000 

7,100 

lb.sq.in. 

1,260 
1,200 
1,050 
1,150 
700 
1,000 
1,200 

800 
700 
800 

2,200 
1,900 
3,000 
1,900 
2,300 
2,000 
1,800 
2,000 
1,600 
1,800 

2,700 
3,100 
2,400 
2,200 
2,700 
2,800 
3,200 

1,200 
2,100 

1,900 
1,700 

1,400 

lb.sq.in. 

835 
770 
770 
800 
400 
500 
800 

500 
400 
500 

1,000 
1,000 
1,100 
900 
1,100 
900 
1,100 
1,100 
900 
900 

1,100 
1,100 
1.000 
1,000 
1,100 
1,200 
1,200 

800 
1,300 

1,100 
1,000 

800 

4.  Loblolly-     "  
-  5.  White         "  
6.  Red             "   
7    Spruce-       "      .  .  .  . 

8    Bald  cypress  .... 

9    White  cedar 

10.  Douglas  spruce  ... 
x*  11    White  oak 

12    Overcup-oa.k 

13    Post- 

14.  Cow- 

15.  lied                 
16    Texan            

*•—  17    Yellow 

18.  Water-           

19    Willow- 

20.  Spanish         

21.  Shagbark  hickory.  . 
22.  Mockernut 
23.  Water- 
24.  Bitternut 
25.  Nutmeg- 
26.  Pecan 
27.  Pignut 

28.  White  elm  

29    Cedar-    "      ... 

30.  White  ash  

31.  Green     " 

32.  Sweet-gum 

EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.     671 

TABLE    XLIX. — CRUSHING  STRENGTH   OF   TIMBER,   ENDWISE,  IN   POUNDS    PER 

SQUARE    INCH    REDUCED   TO   THE   STANDARD    PERCENTAGE    OF   MOISTURE. 

(From  U.  8.  Forestry  Circular,  No.  15.) 


Species. 

Per  cent  of  Moisture  to  which  Re- 
sults are  Reduced. 

Number  of  Tests  Averaged. 

Average  of  all  Tests. 

a 

a* 

c 
1 

I 
K 

o 

0> 

8,600 
9,500 

7,600 
8,700 
6,800 
8,100 
8,800 

8,500 
6,000 
8,100 

11,300 
8,600 
8,100 
9,800 
9,200 
9,800 
8,300 
9.000 
8,700 
9,500 

10,900 
11,600 
9,600 
11,200 
11,000 
10,400 
12,700 

8,800 
10,100 

8,700 
9,800 

8,500 

Average  of  Lowest  Ten  Per  cent. 

Highest  Single  Result. 

Lowest  Single  Result. 

Proportion  of  all  Tests  within  10* 
of  Average. 

Proportion  of  all  Tests  within  25* 
of  Average, 

1    Lonf-leaf  pine  

15 
15 
15 
15 
12 
12 
12 

12 
12 
12 

12 
12 
12 
12 
12 
12 
12 
12 
12 
12 

12 
12 
12 
12 
12 
12 
12 

12 

12 

12 
12 

12 

1,230 
410 
330 
660 
130 
100 
170 

655 

87 

4] 

218 
216 
49 
256 
57 
117 
40 
31 
153 
251 

137 

75 
14 
25 
72 
37 
30 

18 
44 

87 
10 

118 

(  6,900 
*]  7,900 
1  5,900 
L  6,500 
5,400 
6,700 
7,300 

6,000 
5.200 
5,700 

8,500 
7,300 
7,100 
7,400 
7,200 
8,100 
7,300 
7,800 
7,200 
7,700 

6,500 
10,100 
8,400 
9,600 
8,800 
9,100 
10,900 

6,500 
8,000 

7,200 
8,000 

7,100 

5,700 
6,500 
4,800 
5,400 
4,000 
4,900 
5,600 

4,200 
4,400 
4,200 

6,300 
6,000 
6,000 
5,600 
5,500 
6,900 
5,800 
6,300 
5,500 
5,100 

7,500 

8,000 
7.000 
7,800 
7,100 
7,300 
8,900 

5,000 
6,500 

5,700 
6,600 

5,600 

11,900 
10,600 
8,500 
11,200 
8,500 
8,200 
10,000 

9,900 
6.200 
8,900 

12,500 
9.100 
8,200 
11,500 
9,700 
11,300 
8,600; 
9,200 
11.000 
10,600 

13,700 
12,200 
10,000 
11,500 
12,300 
10,000 
13,000 

8,800 
10,600 

9,600 
9,800 

8,900 

3,400^ 
2,800  [ 
4,500  f 
3,900  I 
3,200 
4,300 
4,400 

2,900 
3,200 
4,  ICO 

5,100 
3,700 
5,900 
4,600 
5,400 
5,800 
5,500 
6,200 
4,200 
3,700 

5,800 
6,200 
*6,700 
7,300 
6,400 
5,800 
8,700 

4,900 
6,200 

5,000 
6,600 

4,600 

0.53 
.61 
.47 
.49 
.49 
.54 
.66 

.31 
.79 

.28 

.40 
.70 
.58 
.51 
.36 
.62 
.58 
.75 
.51 
.61 

.79 
.65 
.71 
.60 
.79 
.51 
.72 

.28 
.66 

.48 
.29 

.60 

0.90 
.93 
.90 
.84 
.93 
.9ft 
.95 

.74 
.99 

.65 

.81 
.95 
1.00 
.89- 
.94 
.98 
1.00 
1  00 

.sa 

.94 
.97 

LOO 
1.00 
.97 
.95 
1.00 

.88 
.95 

.9ft 
1.00 

.97 

2.  Cuban           "    

3    Short  -leaf    " 

4    Loblolly-      "     .. 

5.  White           "    

6    Red 

7.  Spruce-        "    .... 

8    Bald  cypress 

9    White  cedar 

10    Douglas  spruce  .... 

11    White  oak 

12.  Overcup  oak     .... 

13.  Post-oak  

14    Cow  oak 

15    Red  oak  

16    Texan  oak  

17    Yellow    " 

18    W:iter-    "    

19.  Willow-"    

20.  Spanish  "    

21.  Sha^bark  hickory  .  .  . 
22.  Mockernut 
23.   Water-              "       ... 
24.  Bitternut 
25.   Nutmeg-          " 
26.  Pecan 
27.  Pignut              " 

28.  White  elm  

29.  Cedar     "    

30.  White  ash  

31.  Green    " 

32.  Sweet-gum  

*  These  results  should  be  increased  from  12  to  15  per  cent  to  reduce  them  to  a 
tandard   moisture  of  12  per  ceiit.     See  table  on  p.  670  for  results  corrected  to  12  per 

ot'tit  moisture. 


672 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE   L.— STRENGTH   OF   GEEEN  TIMBEE   IN  COMPEESSION  ENDWISE. 

This  timber  contained  more  than  forty  per  cent  of  moisture. 
(From  U.  S.  Forestry  Circular,  No.  15.) 


Species. 


1.  Long-leaf  pine 86 

2.  Cuban           "    38 

3.  Short  ]caf     "    8 

4.  Loblolly-      "   69 

7.  Spruce-        "    71 

8.  Bald  cypress 280 

9.  White  cedar 34 

11.  White  oak 25 

12.  Overcup-oak 45 

14.  Cow-oak 58 

16.  Texan  oak 39 

19.  Willow-oak 49 

20.  Spanish  oak 52 

21.  Shaarbnrk  hickory 22 

22.  Mockernut       '      18 

23.  Water-               '       4 

25.  Nutmeg-           '       26 

26.  Pecan                '       4 

27.  Pignut               '       5 

32.  Sweet-gum 6 


Number  of 
Sticks  Tested. 


Average  Com- 

pressive 
Strength  in 
Pounds  per 
Square  Inch. 


4,300 
4,800 
3,300 
4,100 
3,900 

4,200 
2,900 

5,300 
3,800 
3,800 
5,200 
3,800 
3,900 

5,700 
6,100 
5,200 
4,500 
3,600 
5,400 

3,300 


Highest 

Single  Result, 

Pounds  per 

Square  Inch. 


7,300 
6,100 
4,000 
5,500 
4,700 

8,200 
3,400 

7,000 
4,900 
4,900 
6,000 
5,500 
5,100 

6,900 
7,200 
5,600 
5,500 
3,800 
6,200 

3,600 


Lowest 

Single  Result, 

Pounds  per 

Square  Inch. 


2,800 
3,500 
3,000 
2,600 
2,800 

1,800 
2,300 

3,200 
2,800 
2,300 
3,100 
2.300 
2,500 

3,500 
4,500 
4,700 
3,700 
3,300 
4,700 

3,000 


442.  Other  Special  Investigations. — In  addition  to  regular  tests  the 
results  of  which  are  summarized  in  Tables  XLVIII  to  LIU,  the  following 
special  investigations  have  been  in  progress,  the  mechanical  tests  connected 
therewith  being  under  the  author's  supervision.  Some  of  the  conclusions 
stated  below  must  be  accepted  as  provisional,  pending  further  experiments 
along  these  lines. 

1.  The  Effect  of  "  Bleeding  "  (boxing,  or  tapping,  for  turpentine)  long- 
leaf  pine-trees  on  the  qualities  of  the  lumber  subsequently  cut  from  the  same. 
This  investigation  included  1300  mechanical  tests  on  bled  timber  taken  from 
two  sites,  one  where  the  trees  had  been  bled  and  abandoned  for  five  years, 
and  the  other  freshly  bled  and  abandoned.     These  results  were  compared 
with  the  regular  tests  on  unbled  timber.     In  addition  300  chemical  analyses 
were  made  on  bled  and  unbled  timber.     These  investigations  proved  beyond 
a  doubt  that  the  "  bleeding"  of  long-leaf  pine  timber  has  absolutely  no  effect 
on  Us  strength,  and  probably  none  on  its  value  or  life  when  exposed  to  the 
weather.     See  Forestry  Bulletin  No.  8.     (This  conclusion  is  final.) 

2.  Influence  of  Size  on  the  Strength  of  Beams. — This  investigation  included 
433  tests  in  all.     Large  beams  were  first  tested  to  rupture,  and  then  small 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.      673 

TABLE  LI. — STRENGTH  OF  TIMBER  IN  CROSS-BREAKING.  THE  MODULUS  OF 
RUPTURE  REDUCED  TO  THE  STANDARD  PERCENTAGES  OF  MOISTURE. 
POUNDS  PER  SQUARE  INCH. 

(From  U.  S.  Forestry  Circular,  No.  15.) 


Species. 

1 

.c 

_u 
2 

5 

2 

23 

ij 
ll 

«_  5° 
o  5 

4J  CO 

£"s 
^$ 

£* 

15 
15 
15 
15 
12 
12 
12 

12 
12 
12 

12 
12 
12 
12 
12 
12 
12 
12 
12 
12 

12 
12 
12 
12 
12 
12 
12 

12 
12 

12 
12 

12 

Number  of  Tests  Averaged. 

| 

"o, 

3 
« 

O 
«) 

a 

I 
•5 

Average  of  Highest  Ten  per  Cent. 

Average  of  Lowest  Ten  Per  Cent. 

*s 

"3 

1 
t 

£ 

35 
B 

Lowest  Single  Result. 

Proportion  of  Results  within  W%  of 
Average. 

•s 

B 

a 

5 
'i 
Jg 

I 

•8 

|| 

ll 
g<« 

1   Long-leaf  pine  

1,160 
390 
330 
650 
120 
95 
170 

655 

87 
41 

218 
216 
49 
256 
57 
117 
40 
31 
153 
257 

187 
75 
14 
25 
72 
37 
30 

18 
44 

87 
10 

118 

f  10,900 
j  11,900 
*]    9,200 
1  10,  100 
7,900 
9,100 
10,000 

7,900 
6,300 
7,900 

13,100 
11,300 
12  300 
11,500 
11,400 
13,100 
10,800 
12,400 
10,400 
12,000 

16,000 
15,200 
12.500 
15,000 
12,500 
15,300 
18,700 

10,300 
13,500 

10,800 
11,600 

9,500 

14,200 
14,600 
12,400 
13,100 
10,100 
12.300 
13,600 

11,700 
8,400 
12,000 

18,500 
14,900 
15,300 
12,500 
15,400 
16,900 
14,600 
15,700 
13800 
15,600 

20,300 
19,700 
17,300 
19,300 
15,600 
18,100 
24,300 

13,600 
17,300 

14,200 
16,000 

12,700 

8,800 
8,800 
7,000 
8,100 
5,000 
4.900 
5,800 

5,000 
4,000 
4,100 

7,600 
6,300 
7.400 
6,500 
9,100 
10,000 
5,700 
7,200 
5,400 
6,900 

9,400 
7,900 
5,400 
8,700 
8,100 
10,300 
11,500 

7,300 
8,500 

6,300 
5,100 

6,000 

17,800 
17,000 
15,300 
14,800 
11,100 
12,900 
16,300 

14,800 
9,100 
13,000 

20,300 
19,600 
16,400 
23,000 
16,500 
19,500 
15,000 
16,000 
16,000 
17,300i 

23,300 
20,700; 
18,000 
19,500 
16,600 
18,300 
25,000 

14,000 
19,200 

15,000 
16,000 

14,400 

3,300] 
2,900  ! 
5,000  f 
3,9001 
4,600 
3,100 
3,100 

2,300 
3,500 
3,800 

5,700 
4,900 
5,100 
3.300 
5,700 
8,200 
5,100 
5.800 
3.300 
5,000 

*5,700 
5,300 
5,300 
7,000 
6,700 
5,600 
11,100 

7,300 
6,600 

5,000 
5,100 

5,100 

0.41 
.46 
.40 
.44 
.43 
.28 
.43 

.25 
.32 
.22 

.39 
.4" 

.47 
.32 
.46 
.64 
.28 
.40 
.33 
.40 

.46 
.45 
.21 

2S 
]40 
.38 
.43 

.44 
.50 

.37 

.20 

.39 

0.84 
.83 
.70 

.84 
.81 
.60 
.81 

.69 

'.78- 
.58 

.75 

.81 
.92 
.68 
.84 
.86 
.65 
.76 
.70 
.72 

.84 
.78 
.64 
.60 

.88 
.95 

.77 

.72 

.86 

.77 
.60 

.79 

2.  Cuban               

3   Short-leaf 

4.  Loblolly-          

5.  White                

6.  Red                   

7.  Spruce- 

8.  Bald  cypress  

9.  White  cedar 

10.  Douglas  sp~uce  .... 

11.  White  oak  .    . 

12.  Overcup-oak  .  .  . 

13.  Post-           '   

14.  Cow-           '   . 

15.  Red 

16.  Texan         '   

I?  Yellow       '  

18.  Water- 

19.  Willow-      ' 

20.  Spanish      •   .  

21.  Shagbark  hickory.  .  .  . 
22.  Mockernut 
23.  Water- 
24.  Bittern  ut                 ..... 
25.  Nutmeg- 
26,  Pecan 
27.  Pignut 

28.  White  elm         

29.  Cedar-    "    

30.  White  ash.  .  . 
31.  Green     " 

32.  Sweet-gum 

*  These  results  should  be  increased  from  12  to  15  percent  to  reduce  them  to  a  standard 
moisture  of  12  per  cent.     See  table  on  p.  670  for  results  corrected  to  12  per  cent  moisture. 


674 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE    LIT. — ELASTIC  LIMIT  STRENGTH    OF  TIMBER   IN   CROSS-BENDING  AND 
THE   MODULUS   OF     ELASTICITY    IN     POUNDS    PER   SQUARE   INCH,   BOTH 
REDUCED   TO   STANDARD    PERCENTAGES   OF   MOISTURE. 
(From  U.  S.  Forestry  Circular,  No.  15.) 


I 

1 

jj 

a 

05 

3 

I 

S 

5 

3 

§ 

c 

* 

! 

1 

% 

1 

1 

1 

PH 

0 

M 
o 

1 

li 

95 

CQ 

5 

E 

1 

1 

— 

1 

g 

1 

1 

Species. 

5  3 

<j 

o 

r/3 

o 

CO 

1 

"w 

"o 

S 

1 

"3 

"z  i3 

03 

3 

3 

to 

1 

« 

tf 

J 

^  « 

I 

1 

"S+- 

H 

a 

"So 

"to 

o 

«H 

O 

"o  5 

I 

05 

Q;  fcjQ 

"8 

o 
0) 

S 

n 

la 

.2  to 

|| 

1 

S 

tog 

1 

to 

0) 

"cc 
O> 

1 

II 

a"  o3 
> 

Z* 

3 

* 

^ 

^ 

K 

o 

^ 

^ 

1.  Long-leaf   pine  .  . 
2.  Cuban           "     
3.  Short-leaf     "     
4.  Loblolly-       "     .... 
5.  White            "     .... 

15 
15 
15 
15 
12 

r  1,160 

I     390 
*  1     330 
1     650 
130 

1.800.000 
2,300,000 
1.600,000 
1,950.000 
1,^90,000 

8,500 
9,500 
7,200 
8,200 
6,400 

11-300 

r,50o 

10,'800 
8,200 

5,400 
5,600 
4,800 
5,400 
4,500 

13.500 
12,900 
11,900 
12,700 
10,000 

2,400  } 
2,200 
2,900  f 
3.100J 
4,100 

0.43 
.42 

.48 
.46 
.58 

0.81 
.83 
.81 
.85 
.85 

6.  Red                "     .... 

12 

95 

1.620.000 

7.700 

10,300 

4.500 

11,300 

3,100 

.38 

.73 

7.  Spruce- 

12 

170 

1,640,000 

8,400 

11,700 

5,000 

13,700 

3,000 

.51 

.82 

8    Bald  cypress  .  . 

12 

655 

1,290.000 

6.600 

9,900 

4,200 

12,000 

2  200 

.25 

.66 

9.  White  cedar  

12 

87 

910,000 

5800 

7,300 

4,000 

8,200 

3,400 

.44 

.86 

10.  Douglas  spruce.  .. 

12 

41 

1,680,000 

6,400 

9,600 

3,400 

13,700 

2,800 

.32 

.56 

11.  White  oak  

12 

218 

2,090.000 

9,600 

14,100 

6,100 

15,700 

4,400 

.37 

.73 

12.  Overcup-oak  

12 

216 

1,620,000 

7,500 

9,500 

5,400 

11  600 

4,000 

.47 

.91 

13.  Post-                

12 

49 

2,030,000 

8,400 

9,600 

6,000 

10,600 

5,100 

.34 

14.  Cow-                

12 

256 

1,610,000 

7,600 

11,600 

5,000 

14,200 

3,400 

.50 

!95 

15.  Red                 

12 

57 

1,970.000 

9,200 

13,600 

5  600 

14,500 

5,100 

.15 

.49 

16.  Texan             

12 

117 

1,860,000 

9,400 

11,400 

7,800 

12,000 

5,950 

.94 

17.  Yellow           

12 

40 

1,740,000 

8.100 

11,100 

5,100 

1  1  ,800 

4,900 

!35 

.75 

18.  Water-            

12 

31 

2,000,000 

8,803 

11,400 

5,500 

11,800 

4,500 

.40 

.84 

19.  Willow-          
20.  Spanish          

12 
12 

153 
257 

1,750,000 
1,930,000 

7,400 
8,600 

10,000 
11,600 

4,300 
6,600 

13,100 
13,500 

2,700 
5,100 

.42 
.41 

.81 
.80 

21.  Shagbark  hickory. 

12 

187 

2,390,000 

11.200 

14,200 

7,700 

16.100 

5,400 

.50 

.89 

22.  Mockernut 

12 

75 

2,320,000 

11,700 

14,600 

7,800 

15,400 

4,300 

.39 

.83 

23.  Water- 

12 

14 

2,080.000 

9.800 

11.800 

4  800 

11,900 

4,109 

.21 

.86 

24.  Bitternut 

12 

25 

2,280,000 

HJOO 

14,000 

7,600 

14,300 

7,500 

.44 

.84 

25.  Nutmeg- 

12 

72 

1,940,000 

9,300 

11,300 

6,400 

12,200 

4.200 

.46 

.93 

26.  Pecan                 ' 

12 

37 

2,530.000 

11.600 

14,400 

7,900 

15,000 

5,800 

.65 

.89 

27.  Pignut                ' 

12 

30 

2,730,000 

12,600 

16,400 

8,300 

17,000 

7,400 

.40 

.83 

28.  White  elm.  .  . 

12 

18 

1,540,000 

7,300 

9,600  ; 

5,400 

9.700 

5,300 

.33 

.71 

29.  Cedar-   "   

12 

44 

1,700,000 

8,000 

10,100 

5,800 

10,700 

4,700 

.57 

.91 

30.  White  ash... 
31.  Green    "    

2 

12 

87 
10 

1,640.000 
2,050,000 

7,900 

8,900 

10,400 
13,200 

5,200 
3,200 

11.500 
13,200 

3,600 
3,200 

.'40 

.83 
.70 

32.  Sweet-gum    . 

12 

118 

1,700,000 

7,800 

10  100 

QO 

1 

'° 

.  O* 

*  These  results  should  be  increased  from  12  to  15  per  cent  to  reduce  them  to  a  standard  moisture 
of  12  per  cent.    See  results  corrected  to  12  per  cent  moisture  in  table  on  p.  670. 

t  This  is  the  Apparent  Elastic  Limit  Strength  found  as  described  iu  Art.  13,  p.  18. 

(4-in.)  sticks  were  cut  from  the  uninjured  ends,  from  the  top  side  at  one 
end  and  from  the  bottom  side  at  the  other  end.  These  results  prove  the 
truth  of  the  proposition  announced  in  (3)  on  page  4G2.  (This  conclusion  is 
also  probably  final.) 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.      675 


TABLE  LIII. — STRENGTH  OF  TIMBER  IN  CRUSHING  ACROSS  THE  GRAIN  RE- 
DUCED TO  STANDARD  PERCENTAGES  OF  MOISTURE,  IN  SHEARING  WITH 
THE  GRAIN,  IN  POUNDS  PER  SQUARE  INCH,  THE  SPECIFIC  GRAVITY, 
AND  THE  WEIGHT  PER  CUBIC  FOOT,  THESE  NOT  BEING  REDUCED  TO 
STANDARD  MOISTURE. 

(From  U.  S.  Forestry  Circular,  No.  15.) 


Species. 

Number  of 
Tests 
Averaged. 

Crushing- 
strength 
Across  the 
Grain. 

Shearing- 
strength 
with  the 
Grain. 

Average 
Specific 
Gravity. 

Average 
Weight 

Cubic 
Foot. 

1    Long-leaf  pine  

1,210 

f  1,0001 

700 

0.61 

38 

2    Cuban          ' 

400 

J  1  000  1 

700 

.63 

39 

3    Short  leaf    '                            

330 

*  1      900  [ 

700 

.51 

32 

4    Loblolly-     '    

•      690 

I  i.oooj 

700 

.53 

33 

5.  White           '     

130 

700 

400 

.38 

24 

6    Red              '     

100 

1.000 

500 

.50 

31 

7.  Spruce-       '     

175 

1,200 

800 

.62 

39 

8    Bald  cypress  

650 

800 

500 

.46 

29 

9    White  cedar.  .  .  .-  

87 

700 

400 

.37 

23 

10.  Douglas  spruce  

41 

800 

500 

.51 

32 

11.  White     oak  ,  

218 

2,200 

1,000 

.80 

50 

12    Overcup-    '  .  .               .    . 

216 

1  900 

1  000 

74 

46 

13    Post-           *  

49 

3  000 

1  100 

80 

*    50 

14    Cow-              

256 

1,900 

900 

.74 

46 

15    Red 

57 

2  300 

1  100 

.72 

45 

16    Texan            .  .                      

117 

2,000 

900 

73 

46 

17    Yellow          

40 

1,800 

1,100 

.72 

45 

18    Water-           

30 

2,000 

1,100 

.73 

46 

19    Willow-                ....           

153 

1,600 

900 

.72 

45 

20    Spanish         

255 

1,800 

900 

.73 

46 

21    Shagbark  hickory    ...        

135 

2,700 

1  100 

.81 

51 

75 

3,100 

1,100 

.85 

53 

23    Water-                     

14 

2,400 

1,000 

.73 

46 

24    Bittern  ut                           .          .  .  .  . 

25 

2,200 

1,000 

.77 

48 

25    Nutnie0"-                    

72 

2,700 

1,100 

.78 

49 

26    Pecan                      ,  -  

37 

2,800 

1,200 

.78 

49 

27    Pignut              '                  

30 

3,200 

1,200 

.89 

56 

28    White  elm  

18 

1,200 

800 

.54 

34 

29    Cedar-    "                   

44 

2,100 

1,300 

.74 

46 

30    While  ash    

87 

1,900 

1,100 

.62 

39 

10 

1,700 

1,000 

.62 

39 

32    S  weet-fum  

118 

1,400 

800 

.59 

37 

*  These  results  should  be  increased  from  12  to  15  per  cent  to  reduce  them  to  12  per 
cent  moisture.     See  results  corrected  to  12  per  cent  moisture  in  table  on  p.  670. 

3.  The  Strength  of  Large  Columns  as  compared  with  the  Crushing 
Strength  of  Short  Blocks. — This  investigation  has  not  yet  progressed  far 
enough  to  enable  a  definite  law  to  be  announced,  but  they  seem  to  justify  the 
column  formulae  given  in  Art.  44G,  p.  G82. 


676  TEE  MATERIALS  OF  CONSTRUCTION. 

4.  Variation  of  Strength  ivitli  Position  across  the  section  of  a  log,  and 
also  vertically  in  the  trunk  of  the  tree.    These  investigations  are  still  incom- 
plete. 

5.  Relation  of  Strength  to  Moisture  Condition. — This  was  made  the  sub- 
ject of  a  special  investigation  involving  18G6  tests  on  small  sticks  two  inches 
square.     The  laws  derived  from  the  larger  tests  were  fully  borne  out.     (Con- 
clusion final.) 

6.  The    Uniformity  of  the  Distribution  of  Moisture  in  green  and  dry 
wood.     The  results  showed  that  in  sticks  in  which  the  moisture  was  evenly 
distributed  when  green  it  remained  evenly  distributed  longitudinally  while 
drying,  the  moisture  percentages  having  been  determined  by  taking  full 
cross-sections  J-inch  thick  entirely   across  the  section.     A  difference  was 
observed  in  the  moisture  determinations  as  between  disks  -J  and  f  inch 
thick,  which  the  author  attributes  to  the  drying  effect  of  the  currents  of  air 
carried  by  the  saw  in  cutting  off  the  disks,  this  being  relatively  greater  with 
the  thinner  sections.     For  this  reason  borings  are  better,  but  they  cannot 
represent  equally  all  parts  of  the  cross-section  as  does  the  disk  specimen. 
Disks  cut  with  a  rapidly  moving  circular  cutting-off  saw  exhibited  the  effects 
of  this  drying  action  more  than  those  cut  with  a  hand-saw.     There  is  always 
very  much  more  moisture  in  green  sap-wood  than  in  green  heart-wood. 

7.  *TJie   Weakening  Effect  of  Reabsor~bed  Moisture  is  the  same  as  that 
originally  in  the  green  timber.     To  determine  this  224  tests  of  strength 
in  compression  endwise  were  made  on  sticks  2  inches  square,  one  half  of 
which  were  on  the  sap-wood  and  the  remainder  on  the  heart-wood  of  a  single 
slab  of  short-leaf  pine  4  inches  thick  cut  especially  for  these  tests  and  brought 
at  once  to  the  laboratory.     Identical  material  (alternate  sections)  of  sticks 
cut  from  this  plank  were  used  for  the  diminishing-moisture  and  for  the 
increasing-moisture  series,  the  reduction  in  moisture  being  carried  to  as  near 
zero  as  was  possible  for  testing  in  the  open  air,  as  the  specimens  reabsorb 
moisture  very  rapidly  when  removed  from  the  dryer.     Unfortunately  the 
conditions  of  moisture  were  not  as  well  distributed  as  was  planned,  but  the 
results,  as  plotted  in  Fig.  601  for  the  sap-wood,  are  sufficient  to  show  that 
the  weakening  effect  of  a  given  percentage  of  moisture  is  the  same  whether 
this  moisture  be  the  original  sap  in  the  tree  or  whether  it  be  reabsorbed  water 
after  the  timber  has  been  thoroughly  seasoned  or  dried.     (Conclusion  prob- 
ably final.) 

It  also  incidentally  developed  that  the  maximum  strength  corresponds  to 
about  3  or  4  per  cent  of  moisture.  Since  it  is  impossible  to  have  wood,  in 
any  kind  of  service,  at  so  low  a  moisture  percentage  (8  or  10  per  cent. being 
about  a  normal  indoor  minimum),  this  moisture  condition  of  maximum 
strength  has  no  economic  significance. 

8.  The  Effect  of  Hot-air  Drying  on  Strength. — Two  hundred  tests  were 
made  to  determine  this,  with  the  result  that  for  any  temperature  commonly 
used  in  drying  lumber  no  detrimental  effect  on  strength  would  be  produced^ 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.     677 

aside  from  the  checking  action  which  might  result  from  a  too-rapid  drying  of 
the  exterior  portions  of  the  sticks.     (Conclusion  probably  final.) 

9.  The  Effect  of  Very  High  Temperatures  and  Pressures  used  in  Drying 
(as  in  the  "  vulcanizing  "  process) . — In  this  investigation  210  mechanical 
tests  were  made  on  exactly  similar  material  (long-leaf  pine  4  inches  square), 
a  part  of  which  had  been  submitted  to  the  vulcanizing  process  in  New  York 
City,  while  the  corresponding  specimens  had  been  dried  by  an  air-blast  at 
about   100°  F. ;  many  chemical    analyses  were  also  made  to  find    if   any 
chemical  changes  had  occurred.      The  results  showed  a  slightly  less  strength 
for  the  "vulcanized"  specimens,  for  like  percentages  of  moisture,  with  no 
appreciable  chemical  change.     (Conclusion  provisional.) 

10.  The  Effect  of  Long  Immersion  in  Water  on  Strength. — In  this  inves- 
tigation 65  tests  of  strength  have  been  made  on  material  soaked  in  water  for 
many  months  and  the  results  compared  with  those  on  similar  material  (alter- 
nate sections  of  the  same  sticks),  which  passed  through  the  regular  tests. 
So  far  as  these  tests  go  they  indicate  no  loss  of  strength  for  six  months'1  soak- 
ing in  water.     (Conclusion  provisional.) 

Many  other  special  investigations  have  been  planned,  but  not  yet  execute'd 
for  want  of  funds.* 

443.  Relations  of  Weight  and  Strength,  f— "  That  within  the  same 
species  the  strength  of  wood  varied  with  the  dry  weight  (specific  gravity), 
i.e.,  that  the  heavier  stick  is  the  stronger,  has  been  known  for  some  time. 
That  this  law  of  variation  held  good  not  only  for  a  given  species,  but  from 
species  to  species,  in  the  pines  of  our  Southern  States,  was  indicated  in  Cir- 
cular No.  12  of  this  Division.  This  fact  becomes  the  more  important  in 
practical  application,  as  the  wood  of  these  species  of  pines  cannot  as  yet  be 
disinguished  at  all  by  its  anatomical  structure,  and  only  with  difficulty  and 
uncertainty  by  other  appearances,  while  in  the  lumber  market  substitution 
is  not  infrequent.  (See  Art.  447.)  It  will,  therefore,  be  best  with  these 
pines,  when  strength  alone  is  desired,  to  inspect  the  material  by  finding  the 
specific  gravity  (or  weight  per  cubic  foot),  neglecting  the  species  determina- 
tion altogether. 

"  While  this  result  of  the  exhaustive  series  of  tests  has  been  demonstrated 
for  these  pines  and  may  be  considered  of  great  practical  valne,  we  can  now 
extend  the  application  of  the  law  of  relation  between  weight  and  strength  a 
step  farther,  and  state  as  an  indication  of  our  tests  that  probably  in  woods 
of  uniform  structure  strength  increases  with  specific  weight,  independently  of 
species  and  genus  distinction;  i.e.,  ceteris  paribus,  the  heavier  wood  is  the 
stronger. 

*A11  experimental  work  stopped  in  March,  1896.  It  had  been  interrupted  several 
times  previously  for  lack  of  means.  No  special  appropriation  has  ever  been  made  for 
this  work.  It  has  all  been  done  with  small  allotments  made  from  the  annual  appropria- 
tions for  the  Forestry  Division. 

f  Dr.  Fernow,  in  Circular  15. 


678 


THE  MATERIALS  OF  CONSTRUCTION. 


11  We  are  at  present  inclined  to  state  this  important  result  with  caution 
only  as  a  probability  or  indication  until  either  the  test  material  and  tests  can 
be  more  closely  scanned,  or  other  more  carefully  planned  and  minutely 
executed  series  of  detail  tests  can  be  carried  on  to  confirm  the  truthtof  what 
the  wholesale  tests  seem  to  have  developed. 

"  In  Figs.  G03  and  604  the  average  strength  of  the  different  species  m 


12,000 


11.000 


lOpOO 


6,000 


WCfDAR 


• 


rL ASS  W RUCE 


CUBIC 


m 


UM 


FOOT  I* 


'S 


POV/VUS 


40          45          50          55         60 
FIG.  603.— Showing  the  Relation  between  Weight  and  Crushing-endwise  Strength  of 
Various  Timbers  at  the  standard  (12$)  moisture,  except  the  Southern  pines,  Nos.  1,  2, 
3,  and  4,  which  are  plotted  to  15  per  cent  moisture.     ( U.  S.  Forestry  Circular,  No.  15.) 
compression  endwise  and  in  cross-bending,  as  found  in  Tables  XLIX  and; 
LI,  has  been  plotted  with  reference  to  the  dry  weight  as  given  in  Table 
XLVIIL* 

"  Considering  that  these  tests  and  weight  determinations  (especially  the 
latter)  were  not  carried  on  with  that  exactness  which  would  be  required  for 
a  scientific  demonstration  of  a  natural  law,  that  other  influences,  as  cross- 
grain,  unknown  defects,  and  moisture  conditions,  may  cloud  the  results,  and 
that  in  the  averaging  of  results  undue  consideration  may  have  been  given  to 
weaker  or  stronger,  heavier  or  lighter  material,  the  relation  is  exhibited  in 
spite  of  these  wholesale  methods  with  a  remarkable  degree  of  uniformity, 
bordering  on  demonstration. 

"  An  exception  is  apparent  in  the  oaks  in  that  they  do  not  exhibit  the 
same  relation  of  strength  to  weight  shown  to  exist  in  the  other  species,  anc  j 
also  there  is  a  less  definite  law  among  the  various  species  of  oak  when  takei 


*  The  results  on  the  Southern  pines,  when  reduced  to  12  per  cent  moisture,  as  in  th 
table  on  p.  670,  fall  from  600  to  1100  pounds  higher  in  Fig.  603  and  from  900  to  170 
pounds  higher  in  Fig.  604.— J.  B.  J. 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.     679 


by  themselves.  The  structure  of  oak  wood  being  exceedingly  complicated 
and  essentially  different  from  that  of  the  wood  of  all  other  species  under  con- 
sideration (see  Figs.  88  and  123),  it  may  reasonably  be  expected  that  this 
species  will  not  range  itself  with  the  others.  In  addition,  the  difficulty  of 


17000 


14,000 


/3.000 


^ 


X 


fDAP 

WE/&H 


Pffi 


Cl/B/C 


&A 


&MUCE 


/A 


\R  ELM 


25 


35  45         SO         55        60 

FIG.  604.  —  Showing  the  Relation  between  Weight  and  Cross-breaking  Strength  of 
Various  Timbers  at  the  Standard  (12$)  moisture,  except  the  Southern  pines,  Nos.  1, 
2,  3,  and  4,  which  are  plotted  to  15  per  cent  moisture.  (  U.  S.  Forestry  Circular, 
No.  15,  1897.) 

seasoning  oak  without  defects,  or  of  even  securing  perfect  material,  may  have 
influenced  the  results  of  tests  so  as  to  cloud  the  -»*elationshix)  within  the  genus. 


680  THE  MATERIALS  OF  CONSTRUCTION. 

"  If  further  close  study,  supplemented  by  additional  series  of  tests  care- 
fully devised  to  investigate  this  relationship,  should  uphold  the  truth  of  it, 
this  result  may  be  set  down  as  the  most  important  practical  one  that  could 
be  reached  by  these  tests,  for  it  would  at  once  give  into  the  hands  of  the 
wood-consumer  a  means  of  determining  the  relative  value  of  his  material  as 
to  strength  and  all  allied  properties  by  a  simple  process  of  weighing  the  dry 
material;  of  course  with  due  regard  to  the  other  disturbing  factors  like 
cross-grain,  defects,  coarseness  of  grain,  etc. 

For  instance,  we  would  then  have,  from  the  results  plotted  in  Figs. 
603  and  604,  approximately: 

Crushing  strength  endwise   of  all  timbers  except  the  oaks,  in  pounds  per 
square  inch  =  192  times  dry  weight  in  pounds  per  cubic  foot.     .     (I) 

Cross-breaking  strength  of  all  timbers  except  the  oaks,  in  pounds  per  square 
inch  =  300  times  dry  weight  in  pounds  per  cubic  foot.      .     .     .     (2) 

It  thus  appears  that  if  the  above  law  should  be  established  it  will  only 
be  necessary  to  determine  the  weight  per  cubic  foot  of  any  timber  (perhaps 
not  including  the  oaks),  in  order  to  be  able  to  predict  its  strength,  at  least 
when  used  for  beams  and  columns 

444.  The  Factor  of  Safety  to  be  used  in  timber-structure  designing  is 
now  almost  wholly  a  factor  of  ignorance,  a  large  part  of  which  ignorance  it 
is  the  object  of  the  U.  S.  Timber  Tests  to  dispel,  as  is  well  stated  by  Dr. 
Fernow  in  Circular  Xo.  15,  as  follows: 

"As  to  factors  of  safety  it  may  be  proper  to  state  that  the  final  aims  of  the 
present  investigations  may  be  summed  up  into  one  proposition,  namely,  to  establish 
rational  factors  of  safety.  It  will  be  admitted  by  all  engineers  that  the  factors  of 
safety  as  used  at  present  can  hardly  be  claimed  to  be  more  than  guesswork.  There 
is  not  an  engineer  who  could  give  account  as  to  the  basis  upon  which  numerically 
the  factors  of  safety  for  wood  have  been  established  as  '  8  for  steady  stress,  10  for 
varying  stress,  15  for  shocks'  (see  Merriman's  Text-book  011  the  Mechanics  of  Ma- 
terials) ;  or  as  4  to  5  for  'dead'  load,  and  5  to  10  for  'live'  load  (see  Rankine's 
Handbook  of  Civil  Engineering}. 

"  The  directions  for  using  these  indeterminate  factors  of  safety,  as  given  in  the 
text-books,  would  imply  that  the  student  or  engineer  is,  after  all,  relying  on  his 
judgment  as  to  the  modification  he  should  make  of  such  factors  ;  that  is,  he  is  to  add 
to  this  general  guess  his  own  particular  guess.  The  factor  of  safety  is,  in  the  main, 
an  expression  of  ignorance  or  lack  of  confidence  in  the  reliability  of  values  of 
strength  upon  which  the  designing  proceeds,  together  with  an  absence  of  data  upon 
which  to  inspect  the  material,  and  a  provision  for  decay.  With  a  larger  number  of 
well-conducted  tests  coupled  with  a  knowledge  of  the  quantitative  as  well  as  quali- 
tative influences  ot  various  factors  upon  strength,  and  with  definite  data  of  inspec- 
tion which  allow  ready  sorting  of  material,  the  factor  of  safety,  as  far  as  it  denotes 
the  residuum  of  ignorance  which  may  be  assumed  to  remain,  as  to  the  character 
and  behavior  of  the  material,  may  be  reduced  to  a  minimum,  restricting  itself 
mainly  to  the  consideration  of  the  indeterminable  variations  in  the  actual  and  legiti- 
mate application  of  load,  and  to  a  provision  for  wear  and  decay. 

"  While  the  values  given  in  these  tables  may  claim  to  contain  more  elements  of 
reliability  than  most  of  those  published  hitherto,  much  more  work  will  have  to  be 
done  before  the  above-stated  aim  will  be  satisfied." 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.     681 


445.  Safe  Loads  for  Rectangular  Long-leaf  Yellow-pine  Beams. — Both 
Prof.  Lanza's  tests  on  wooden  beams  and  those  conducted  by  the  author 
show  that  beams  having  a  shorter  length  than  twenty  times  the  depth  under 
a  uniformly  distributed  load,  or  less  than  ten  times  the  depth  under  concen- 
trated loads,  should  be  dimensioned  for  shearing  lengthwise.  As  the  total 
load  which  will  cause  the  beam  to  shear  is  independent  of  the  length,  when 
shearing  occurs  before  rupture  in  cross-breaking,  the  following  table  gives  a 
constant  load  for  all  lengths  shorter  than  the  least  length  for  rupture  in 
cross-breaking.  The  table  is  based  on  a  modulus  of  rupture  of  1250  Ibs.  per 
square  inch,  or  two  thirds  more  than  allowed  for  white-pine  beams  in 
Carnegie's  Handbook.  This  is  in  accordance  with  the  instructions  there 
given.  It  gives  a  factor  of  safety  of  5  on  green  beams  and  of  8  on  dry 
beams,  when  known  to  be  either  long-leaf  or  Cuban  yellow  ("Georgia") 
pine.  For  white  pine,  cypress,  and  Oregon  fir  take  65  per  cent  of  these 

TABLE     LIV.  —  SAFE     UNIFORMLY      DISTRIBUTED      LOADS      ON     LONG-LEAF 

YELLOW-PINE    BEAMS.       BEAM    ONE    INCH   THICK. 
For  other  thicknesses,  multiply  the  tabular  values  by  the  thickness  of  the  beam. 


Span 

Kind 
of 

Depth  of  Beam  in  Inches. 

Kind 
of 

feet. 

Stress. 

Stress. 

6 

7' 

8 

9 

10 

ii 

13 

18 

14 

15 

16 

5 

o 

500 

580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

6 

o  fco 

500 

580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

7 

*-'  Q 

500 

580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

8 

^  o 

500 

580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

9 

"IS 

500 

580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

. 

PH 

ii 

10 

500 

580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

o 

11 

450 

1580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

. 

12 

420 

570 

|670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

1 

13 

'i 

380 

520 

|670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

EH 

14 

j 

350 

480 

630 

830 

920 

1000 

1080 

1170 

1250 

1330 

. 

15 

1 

330 

450 

600 

830 

920 

1000 

1080 

1170 

1250 

1330 

.2 

16 

^ 

320 

425 

550 

1830 

920 

1000 

1080 

1170 

1250 

1330 

r^ 

17 

300 

400 

520 

670 

"8201920 

1000 

1080 

1170 

1250 

1330 

QQ 

18 

a5 

280 

375 

480 

630 

770  [I  980 

1000 

1080 

1170 

1250 

1330 

3 

19 

^ 

270 

350 

470 

600 

730  880 

1000 

1080 

1170 

1250 

1330 

§ 

20 

1 

cc 

250 

330 

450 

570 

690 

850 

1000 

1080 

1170 

1250 

1330 

1 

21 

1 

240 

320 

425 

540 

650 

810 

950 

1080 

1170 

1250 

1330 

3 

23 

0 

230 

310 

400 

520 

620 

770 

910 

1070 

1170 

1250 

1330 

P5 

23 

0 

220 

300 

380 

490 

600 

730 

970 

1020 

1170 

1250 

1330 

24 

8 

210 

280 

370 

470 

575 

700 

830 

975 

1140 

1250 

1330 

a 

25 

S3 

200 

270 

350 

450 

550 

675 

800 

930 

1100 

1250 

1330 

26 

"w 

190 

260 

340 

430 

530 

650 

770 

900 

1060 

1200 

1330 

27 

PS 

180 

250 

330 

420 

520 

620 

740 

870 

1020 

1150 

1320 

^^^^™* 

28 

175 

240 

320 

400 

500 

600 

710 

840 

975 

1110 

1270 

29 

175 

230 

300 

380 

480 

580 

680 

820 

930 

1070 

1230 

682 


TEE  MATERIALS  OF  CONSTRUCTION. 


loads.     For  short-leaf  yellow  pine,  Norway  pine,  spruce,  oak,  elm,  and  ash, 
take  80  per  cent  of  these  loads. 

446.  Strength  of  Wooden  Columns. — A  sufficient  number  of  tests  of 
columns  has  not  as  yet  been  made  by  the  U.  S.  Forestry  Divisionon  which 
to  base  a  general  column  formula.  There  was  published,  however,  in  the 
Report  of  Tests  made  at  the  Watertown  Arsenal  for  1882  a  very  complete 
series  of  tests  of  full-size  columns,  the  average  results  of  which  are  recorded 
in  Tables  LVI  and  LVII  and  plotted  in  Fig.  G05.  There  were  nearly  200 
columns  tested,  part  being  white  and  part  "  yellow  "  pine.  What  particular 
species  of  yellow  pine  was  used  was  not  determined.  Neither  was  the  moist- 
ture  condition  of  the  timber  examined.  Judging  from  the  results  the 
timber  must  have  been  comparatively  green.  In  a  number  of  instances  two 
or  three  sticks  were  bolted  and  keyed  together,  but  in  no  instance  did  they 

TABLE    LV. — SAFE    CONCENTRATED    LOADS    ON    LONG-LEAF    YELLOW-PINE 

BEAMS.       BEAM    ONE    INCH   THICK. 
For  other  thicknesses,  multiply  the  tabular  values  by  the  thickness  of  the  beam. 


Span 
in 

Kind 
of 

Depth  of  Beam  in  Inches. 

Kind 
of 

Feet. 

Stress. 

Stress. 

6 

r 

8 

9 

10 

11 

is 

18 

14 

15 

16 

5 

"500" 

|580 

670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

6 

430 

570 

|670 

750 

830 

920 

1000 

1080 

1170 

1250 

1330 

fcb 

a 

7 

370 

480 

630 

|750 

830 

920 

1000 

1080 

1170 

1250 

1330 

'§ 

8 

320 

425 

560 

700 

|830 

920 

1000 

1080 

1170 

1250 

1330 

j=ii 

9 

, 

280 

380 

490 

675 

~ 

|920 

1000 

1080 

1170 

1250 

1330 

W  0 

10 

1 

250 

340 

440 

560 

690 

840 

1000 

1080 

1170 

1250 

1330 

Jl 

11 

^ 

225 

310 

410 

510 

630 

770 

910  ||1080 

1170 

1250 

1330 

12 

* 

0 

210 

280 

370 

470 

575 

700 

830   980 

1170 

1250 

1330 

QQ 

"JR 

13 

190 

260 

340 

430 

530 

650 

775   900 

1050 

11250 

1330 

O 

PH 

14 

tJb 

175 

240 

315 

400 

490 

600 

720 

840 

970 

1110 

1330 

a 

~^_— 

15 

a 

165 

225 

300 

375 

470 

560 

670 

780 

910 

1040 

1180 

16 

M 

160 

210 

275 

355 

430 

525 

625 

730 

850 

980 

1110 

17 

150 

200 

260 

335 

410 

495 

590 

690 

800 

920 

1050 

fcb 

18 

o 

140 

190 

240 

315 

385 

470 

560 

650 

760 

870 

990 

^3 

19 

0 

135 

175 

235 

300 

365 

445 

530 

620 

720 

820 

940 

p 

20 

o 

<D 

125 

165 

225 

285 

345 

425 

500 

590 

680 

780 

890 

|| 

21 

0 

120 

160 

210 

270 

325 

405 

475 

560 

650 

740 

850 

'"*  h-3 

22 

* 

115 

155 

200 

260 

310 

385 

455 

535 

620 

710 

810 

O  ""oS 

23 

CO 
*55 

110 

150 

190 

245 

300 

365 

435 

510 

590 

670 

770 

24 

9 

« 

105 

140 

185 

235 

290 

350 

415 

485 

570 

650 

740 

a 

25 

100 

135 

175 

225 

275 

340 

400 

465 

550 

620 

720 

.3 

26 

95 

130 

170 

215 

265 

325 

385 

450 

520 

600 

680 

05 

27 

90 

125 

165 

210 

260  310 

370 

435 

510 

575 

660 

PH 

28 

90 

120 

160 

200 

250 

300 

355 

420 

485 

555 

635 

29 

90 

115 

150 

190 

240 

290 

340 

410 

465 

535 

615 

. 

1 

*  See  Lanza's  Applied  Mechanics, 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.      683 

act  as  one  solid  stick  would  have  done,  but  always  as  two  or  three  single 
sticks  would  have  acted  if  placed  freely  in  the  machine  side  by  side,  thus 
proving  that  in  all  cases  of  composite  wooden  posts  they  must  be  treated  as 
separate  members,  each  taking  its  portion  of  the  total  load,  and  deflecting  as 
though  it  stood  alone.  A  great  deal  of  bad  and  even  dangerous  designing 
has  resulted  from  violating  this  principle,  and  doubtless  many  fatal  accidents 
have  resulted  from  such  a  practice.  It  will  be  observed  the  composite  mem- 
bers do  not  lie  appreciably  higher  in  Fig.  605  than  the  single  sticks.  Thus 


0  to  20  3ff  40  so          ~~  60 

FIG.  605.  —  Tests  of  Full-size  Comparatively  Green  Pine  Columns  made  at  the  U.  S. 
Watertown  Arsenal.  (See  Report  for  1882.)  Each  point  plotted  represents  the 
average  of  three  tests. 

three  sticks  of  yellow  pine,  5.5  in.  by  11.9  in.  and  15  feet  long,  carried 
singly  an  average  of  3470  Ibs.  per  square  inch.  When  exactly  similar  sticks 
were  joined  in  pairs  with  packing-blocks  and  bolts,  they  carried  in  one  test 
3870  Ibs.  per  square  inch,  and  in  another  test  3530  Ibs.  per  square  inch; 
whereas  if  they  had  acted  as  one  solid  post  they  should  have  carried  4300 
Ibs.  per  square  inch.  When  three  sticks  4.8  in.  by  11.5  in.  by  15  feet  long 
were  packed  and  bolted  side  by  side,  they  still  deflected  sideways,  though 
1C.  4  in.  across  now  in  this  direction  as  against  11.5  in.  in  the  other  plane, 
and  they  carried  3110  Ibs.  per  square  inch  in  the  one  case  and  3130  Ibs.  per 
square  inch  in  the  other.  If  they  had  acted  as  a  single  stick,  they  would 
have  deflected  in  the  other  plane  and  at  a  load  of  4300  Ibs.  per  square  inch. 
Similar  results  were  obtained  on  white  pine  as  shown  in  Table  LVII  and  in 
Fig.  G05. 

These  results  also  indicate  that  the  author's  parabolic  column  formula  fit 
the  experiments  as  well  as  any  curve  could,  and  hence  he  has  drawn  such 
curves  in  Fig.  605,  and  there  given  their  equations,  these  being,  for  relatively 
green  timber: 

Ultimate  strength  for  green  yellow-pine  columns, 


=  4500  -  1.0 


(1) 


684  TEE  MATERIALS  OF  CONSTRUCTION. 

Ultimate  strength  for  green  ivhih-pine  columns, 

p  =  2500  —  0.5  f^y  ........     (2) 

For  dry  timber  these  would  become  . 

Ultimate  strength  for  dry  Ung  -leaf  pine  columns, 


p  =  8000-  2.0         .....   "...     (3) 
Ultimate  strength  for  dry  wliite-pine  columns, 

p  =  5000  —  1.0  (j)  ........     (4) 

If  the  same  factors  of  safety  be  used  here  as  were  used  in  the  tables  of 
working  loads  on  wooden  beams,  namely,  8  for  dry  and  5  for  green  timber, 
we  would  have  : 

Working  load  per  square  inch  for  long-leaf  pine  columns, 


Working  load  per  square  inch  for  white-pine  columns, 


In  all  the  above  equations  I  —  length  of  column  having  square  ends,  and 
h  =  least  lateral  dimension  of  the  one  or  more  single  sticks  of  which  the 
column  is  composed,  both  dimensions  taken  in  the  same  unit  of  measure. 

447.  How  to  Distinguish  Long-leaf  from  Short-leaf  Pine  Lumber.  —  The 
characteristic  indications  of  these  two  species  of  pine  become  so  merged  that 
it  is  impossible  to  distinguish  them  when  mixed  in  a  consignment.  If  the 
short-leaf  comes  up  to  the  long-leaf  in  specific  gravity,  in  accordance  with 
the  law  laid  down  in  Art.  443,  it  would  not  be  necessary  to  distinguish  them, 
as  they  would  then  be  of  equal  strength  and  value.  As  shown  by  Table 
XLVIII,  the  average  weight  per  cubic  foot  of  dry  long-leaf  pine  is  38  Ibs., 
while  that  of  short-leaf  pine  is  only  32  Ibs.'  But  as  the  lighter  specimens  of 
long-leaf  may  be  no  heavier  than  the  heavier  specimens  of  short-leaf,  this  is 
not  an  absolute  guide. 

The  most  nearly  absolute  criterion  is  the  place  of  its  growth.  The  long- 
leaf  and  short-leaf  pines  do  not  grow  together  to  any  great  extent,  as  shown 
by  Plates  V  and  VI.  These  plates  are  reproduced  from  Forestry  Bulletin 
No.  13  for  the  purpose  of  furnishing  this  particular  criterion. 


PLATE  V. 


T*f~ 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.      685 


TABLE    LVI. — COMPRESSIVE    STRENGTH    OF    UNSEASONED    YELLOW-PINE 

COLUMNS. 

(From  Hep.  Wat.  Ars.  Tests,  1882.) 


!         C 

§ 

£                  °w 

'7. 

•^       ~ 

a 

x 

SOS 

to 

5           i          i 

—         3 

*3 

~  55 

S-d 

"o               .S             .- 

OJ       *""* 

Q     d 

="^  - 

2  M" 

0)                    3) 

CC^  C3 

Sj| 

^  '""'  3 

Remarks. 

i! 

*•§ 

11  ill 

lit 

O  e8  >i 

Pi 

11 
£ 

c.9 

p= 

!3a 

0 

|.sl 

I" 

z 

d 

h 

p 

I 

i 

d 

4 

60 

5.48 

5.51 

4868 

38 

11 

3 

90 

5.46 

5.58 

4,537 

57 

16 

3 

120 

5.48 

5.50 

4,738 

76 

22 

3 

150 

5.50 

5.51 

5,077 

95 

27 

3 

180 

5.48 

5.50 

3,962 

114 

33 

3 

210 

5.48 

5.48 

3,242 

133 

38 

2 

240 

5.42 

5.46 

2.868 

154 

44 

3 

270 

5.55 

5.57 

2,064 

169 

49 

3 

300 

5.46 

5.58 

1,856 

190 

55 

3 

330 

5.30 

5.31 

1,709 

216 

62 

3 

80 

7.76 

9.78 

4,085 

36 

10 

3 

120 

7.76 

974 

4,603 

54 

16 

3 

160 

7.73 

9.74 

3,935 

72 

21 

3 

200 

7.56 

9.65 

4,384 

92 

27 

3 

240 

7.59 

9.68 

3,494 

108 

31 

3 

280 

7.69 

9.75 

3,300 

126 

36 

3 

320 

7.44 

9.28 

2,873 

149 

43 

3 

180 

5.63 

15.6 

3,658 

111 

32 

4 

180 

6.70 

15.6 

3.594 

93 

27 

3 

180 

8.24 

16.2 

3,445 

76 

22 

3 

180 

4.31 

11.5 

2,663 

145 

42 

Sticks  like  those  "joined  together 

3 

180 

5.52 

11.9 

3,472 

113 

33 

«                      11                   «                       X                                «« 

3 

180 

5.62 

11.7 

3,869 

111 

32 

2  sticks  with  3  packing-blocks 

3 

180 

5.60 

11.7 

3,530 

111 

oo      j  2  sticks  with  packing-blocks  at  the  & 

i  \      points 

3 
3 

180 
180 

5.62 

4.80 

11.6 
11.5 

3,365 
3,110 

111 
130 

32     2  sticks,  keyed,  with  uneven  bearings 
37      3  sticks  with  3  packing-blocks 

3 

180 

4.86 

11.5 

3,130 

128       37      Same,  but  swelled  f  in.  at  centre 

By  demanding  the  way  bills  on  all  consignments  coming  directly  from 
the  mills  to  fill  any  particular  order  (which  is  now  the  almost  universal  cus- 
tom), one  may  learn  the  exact  locality  of  the  timber's  growth,  and  by  refer- 
ence to  Plates  V  and  VI  a  very  high  degree  of  probability  can  be  established 
as  to  the  species.  As  a  rule  the  long-leaf  pine  is  of  much  slower  growth 
than  the  short-leaf,  and  hence  its  annual  rings  are  much  narrower.  It  also- 
contains  more  rosin.  Very  fair  characteristic  views  of  the  standing  timber 
of  these  two  species  may  be  had  from  Figs.  GOG  and  G07.  The  needles  of 


THE  MATERIALS  OF  CONSTRUCTION. 


fc     I 


FIG.  606.— Specimens  of  Long-leaf  Pine-trees  growing  in  Open  Woods 


EXPERIMENTAL    VALUES   OF  THE  STRENGTH  OF  TIMBER.      687 


FIG.  607.— Specimen  of  a  Short-leaf  Pine-tree  growing  in  the  Open.    (Taken  from  V.  S. 

Forestry  Bulletin  No.  13.) 


688 


THE  MATERIALS  OF  CONSTRUCTION. 


TABLE   LVII. — COMPRESSIVE    STRENGTH   OF   UNSEASONED   WHITE-PINE 

COLUMNS. 
(From  Rep.  Wat.  Ars.  Tests,  1882.) 


| 

1 

—      A 

03 

to 

S 

3 

3 

a 

OJ 

§      = 

5 

si 

£  . 
?1 

is 

|1 

ll 

'—  O 
U  — 

S«3 

111 

§       » 

•"^  ~ 

.2  5  §< 
^  ?'J* 

III 

III 

Remarks. 

11 

fa 

"w  tf  ^ 

^  HH  •« 

Ha 

.5  _  S 

f    0«M 

c8~G 

a 

3 

J 

o 

P 

PH 

M 

I 

I 

i 

ti 

h 

P 

V 

1 

2 

15 
60 

5.50 

5.48 

5.50 

5.48 

3,570 
3,400 

9.4 
37.9 

3 
11 

)  These  sticks  were  probably  dryer  than 
J      the  longer  columns 

3 

90 

5.50 

5.50 

2,357 

56.7 

16 

3 

120 

5.46 

5.46 

2,299 

76.1 

22 

3 

150 

5.50 

5.48 

2,643 

94.8 

27 

3 

180 

5.43 

5.43 

2,744 

115 

33 

3 

210 

5.36 

5.36 

1,841 

136 

39 

3 

240 

5.27 

5.28 

1,455 

158 

46 

3 

270 

5.18 

5.19 

1,501 

181 

52 

3 

300 

5.25 

5.25 

952 

198 

57 

3 

330 

5.34 

5.35 

1,080 

214 

62 

3 

80 

7.73 

9.66 

2,527 

35.9 

10 

3 

120 

7.73 

9.70 

2,334 

53.8 

16 

3 

160 

7.66 

9.58 

2,307 

72.4 

21 

3 

200 

7.75 

9.65 

2,225 

89.4 

26 

3 

240 

7.45 

9.40 

2,445 

113 

32 

3 

280 

7.70 

9.62 

2,072 

126 

36 

3 

320 

7.47 

9.36 

2,113 

148 

43 

3 

180 

5.60 

15.6 

1,874 

111 

32 

3 

i80 

6.60 

15.6 

2,204 

95 

27 

3 

180 

8.48 

16.5 

2  222 

74 

21 

3 

180 

4.45 

11.6 

1,672 

139 

40 

Sticks  like  those  joined  together 

3 

180 

5.55 

11.6 

2,432 

112 

32 

"         "       "         '  *            '  * 

3 

180 

4.50 

11.6 

1,792 

139 

40 

2  sticks  with  bolts  and  packing-blocks 

3 

180 

5.60 

11.6 

1,880 

111 

32 

2     "         "         "       "         "            " 

3 

180 

5.60 

11.7 

1,991 

111 

32 

3  sticks  swelled  £  in.  at  centre 

3 

180 

5.60 

11  6 

1,947 

111 

32 

3  sticks  and  3  keys,  bolted 

3 

180 

5.60 

11.7 

1,974 

111 

32 

3  sticks  keyed  at  the  -&  points 

3 

180 

5.60 

11.7 

2,102 

111 

32 

j  2  slicks  keyed  at  ends,  packed  at  cen- 
(      Ire,  but  with  uneven  bearings 

3 

180 

4.98 

11.7 

1,746 

125 

3  sticks  with  3  packing  blocks 

3 

180 

4.86 

11.6 

1,913 

128 

•• 

Same,  but  swelled  f  in.  at  centre 

3 

180 

4.68 

11.7 

1,950 

133 

:  sticks  with  3  packing-blocks 

3 

180 

4.88 

11.6 

1,998 

128 

Same,  but  swelled  f  in.  at  centre 

the  long-leaf  pine  are  some  1~  inches  long,  while  those  of  the  short-leaf  pine 
are  only  about  2  inches  long. 

448.   The  Strength  of  Bamboo  is  very  great  for  its  weight,  as  shown  by 
Table   LVIII.     Thus,  taking  17,300  Ibs.  per  square  inch  as  the  apparent 


EXPERIMENTAL    VALUES  OF  THE  STRENGTH  OF  TIMBER.      689 


TABLE    LVIII.  —  STRENGTH    OF    BAMBOO    IN    CROSS-BENDING. 
(Tests  made  by  the  author.) 


c 
o 

9 

I 

45 

o 

1 

J-s 

.S  -' 
~  "3 

a 

!•=" 

o 

43 

?  sg 

•gt 

i 

*; 

e 

^*-H 

£ 

-—  •  .— 

~  t> 

1 

1 

|3 

a 

4)     . 

3-2 

§   09 

£~ 

H 

lo 

o  ^ 

0,0 

aa 

j£ 

II 
|1 

'£ 

I~ 

c' 

c  5 

o  a 
"-5  a 

3 

|5 

if 

ll 
WCQ 

SM 

II 

II 

|| 

^  S 

il 

sS^ 

=  U  4) 

00, 

O'H 

Cl_i  ~° 

o 

e6-^ 

«  s  a 

C^ 
IH'3 

•sgl 

III 

-1 
tic'f 

umber 
between 

°    .2 

111 

ll 

odulus 
Cross-  be 

odulus  o 
Apparei 

Itirnate 
Specime 

eflection 
Elastic  I 

0)  A.S 
«^S 

0  E  Oi 

S  3«2 

JE.O 

o 

*—  * 

^ 

* 

S 

rt 

S 

^ 

ft 

W 

1.25 

0.91 

24 

3 

0.539 

2,230,000 

19,600 

13,000 

1.1 

0.54 

156 

1.25 

.93 

28 

3 

.578  2,200,000  23,200 

15,800 

3.0 

0.89 

249 

1  16 

.86 

28 

3 

.516!  2,510,000  25,000 

16  400 

2  0 

0  79 

196 

1.04 

0.87 

.78 
.63 

24 
22.5 

3 
3 

.375!  2,500,000  25,800 

.266  2,500.000  25,800 

15,900 
17,200 

2  2 
2.0 

0.65 
0.73 

182 
205 

0.71 

.51 

25 

3 

.203  3,020,000 

27,600 

17,200 

2.3 

0.90 

162 

0.40 

.24 

...... 

7.5 

1 

.053!  2,100,000 

41,10(1' 

23,300 

1.1 

0.28 

337 

0.54 

.38 



8.0 

1 

.029 

1,960,000 

30,900 

19,700 

0.65 

0.21 

245 

Mean  Values 

2,380,000 

27,400 

17,300 

216 

elastic  limit  strength  per  square  inch  of  bamboo  in  cross-breaking  (using  the 
formula  M  =  — ,  and  computing  /for  the  actual  annular  section),  we  find, 

u  1 

by  comparing  with  the  results  in  Table  XLVIII,  that  the  strongest  timber 
there  listed,  namely,  pignut  hickory,  is  far  below  it  in  strength,  having  a 
modulus  at  this  limit  of  only  12, GOO  Ibs.  If  we  compare  the  bamboo  weight 
for  weight  with  this,  the  strongest  timber  found  in  the  Forestry  Division 
tests,  to  give  a  certain  cross-breaking  strength  on  a  given  span,  as  for  instance 
28  inches,  and  taking  the  timber  in  the  form  of  a  solid  rectangular  cross- 
section,  we  find  that  to  carry  a  load  of  440  Ibs.  at  the  centre,  which  was 
carried  by  the  second  specimen  in  Table  LVIII,  it  would  require  a  stick  1.14 
in.  square  in  cross-section.  This  would  weigh  1.4  Ibs.,  whereas  the  bamboo 
specimen  weighed  only  0.58  Ibs.  That  is  to  say,  bamboo  is  just  twice  as 
strong  as  the  strongest  wood  in  cross-bending,  weight  for  weight,  ivlien  the 
wood  is  taken  in  specimens  with  a  square  and  solid  cross-section.  The  same 
holds  true  also  for  crushing  endwise. 

449.  The  Holding  Force  of  Nails. — One  of  the  most  valuable  properties 
of  wood  is  the  facility  with  which  boards  may  be  attached  by  means  of  nails, 
and  the  strength  of  such  attachments.  The  holding  force  of  nails  and  spikes 
in  different  woods  is  therefore  of  considerable  importance.  In  Fig.  608  the 
starting  resistances  against  the  drawing  out  from  dry  oak  wood,  of  nails  hav- 
ing different  styles  of  points,  are  shown  graphically.  The  cut  nails  exhibit 
a  much  greater  holding  force  than  do  the  wire  nails,  and  a  slightly  sharpened 


690 


THE  MATERIALS  OF  CONSTRUCTION. 


point  gives  the  highest  resistance  for  each  species.     This  figure  exhibits  the 
holding  force  of  different  nails,  per  square  inch  of  embedded  surface,  when 


J800 


800 


400 


: 


1 

Or 


Fia.  608.— Relative  Adhesive  Strength  of  Wire  and  Cut  Nails  (in  Oak  Wood)  as  affected 
by  the  shapes  of  their  points.     (Engr.  News,  vol.  xxxi.  p.  24.) 

driven  laterally  into  dry  oak  wood.  Evidently  for  the  softer  woods  the 
resistance  to  drawirg  is  very  muck  less,  and  so  is  the  resistance  when  driven 
endwise  into  the  stick. 


CHAPTER  XXXIII. 


STRENGTH  OF  IRON  AND   STEEL  WIRE,   AND  WIRE  ROPE. 

450.  The  Strength  of  Wire  increases  with  repeated  drawings,  as  indicated 
in  Fig.  609.     As  the  strength  increases  the  ductility  decreases.     By  anneal- 


FIG.  609.— Showing  Increase  in  Strength  in  Drawing  Steel  Wire  three  times  from  0.216 
in.  to  0.10  in.  diameter.     (Rep.  Wat.Ars.,  1890.) 

ing,  the  ductility  is  restored  and  the  strength  again  reduced  preparatory  to 
further  drawing.  The  final  product  is  given  such  a  temper  as  its  particular 
use  demands. 

The  increase  in  the  strength  of  wrought  iron  with  rolling  to  small  rods 
and  then  drawing  through  dies  is  shown  in  Fig.  610,  where  the  diameters 
vary  from  0.8  inch  in  rolled  rods  to  0.001  inch  in  fine  wires,  the  tensile 
strength  increasing  from  50,000  Ibs.  to  110,000  Ibs.  per  square  inch. 

Fig.  249,  p.  309,  contains  stress-diagrams  of  steel  piano-wires  having  a 
tensile  strength  of  about  350,000  Ibs.  per  square  inch.  In  the  same  series 
of  tests  other  wires,  about  0.03  inch  in  diameter,  showed  a  tensile  strength 
as  high  as  447,000  Ibs.  per  square  inch.*  These  wires  were  of  high-carbon 
steel,  practically  free  from  sulphur  and  phosphorus,  the  chemical  composi- 

*  Rep.  Wat.  Ars.  Tests,  1894,  p.  347 


692 


THE  MATERIALS  OF  CONSTRUCTION. 


iion  of  the  strongest  wires  being:  combined  carbon,  0.80;  manganese,  0.17; 
silica,  0.41;  sulphur,  0.015;  phosphorus,  0.020. 


0/0 


WMFWmLLED. 


MO 


FIG.  610. 


The  modulus  of  elasticity  of  these  wires  was  28,400,000,  showing  that 
throughout  the  entire  range  of  tensile  strength  of  steel  from  50,000  to 


/v  < 

S 


l/M. 


M-Ctf 


\ 


TIG.  611.— Average  of  Nine  Tests  in  Tension  on  Steel  Wires,  showing  Relation  of 
Elastic  Limits.     ( Wat.  ATS.  Rep.,  1890.) 

450,000  Ibs.  per  square  inch  the  ratio  of  stress  to  elastic  deformation  is  prac- 
tically constant. 

This  material  has  no  "yield-point,"  such  as  is  always  found  with  the 
low-carbon  steels,  as  appears  f  Jom  the  diagrams  in  Fig.  611.     This  diagram 


STRENGTH  OF  IRON  AND  STEEL    WIRE,  AND    WIRE  HOPE.     693 

exhibits  the  advantage  of  adopting  an  arbitrary  "  apparent  elastic  limit,"  as 
described  in  Art.  13,  p.  18.  As  here  shown  (Fig.  Gil)  this  apparent  elastic 
limit  is  well  above  the  true  elastic  limit,  but  well  below  the  so-called  "  elastic 
limit  "  as  given  in  the  original  published  report  of  this  test.  It  corresponds 
to  a  permanent  set  of  less  than  0.0004  of  the  length  of  the  specimen,  which 
would  be  quite  imperceptible  and  hence  of  no  significance.  The  total 
stretch  of  the  specimen  at  rupture  is  only  2.8  per  cent,  or  about  two  per  cent 
if  measured  after  rupture.  This  is  the  quality  of  wire  commonly  employed 
in  the  manufacture  of  high-grade  wire  rope  for  power  transmission,  cable 
railways,  and  the  like.  Three  per  cent  elongation,  measured  after  rupture, 
is  very  large  for  this  quality  of  material. 

Mr.  J.  Bucknall  Smith  gives  the  following  average  values  of  the  strength 
of  iron  and  steel  wires  * : 

Lbs.  per  Sq.  .In. 

Bright  hard-drawn  iron  wire 80,000 

Bessemer  steel  wire 90,000 

Mild  open-hearth  steel  wire 130,000 

High-carbon  open-hearth  steel  wire 180,000 

Crucible  cast  steel  wire  (patent  tempering) 220,000 

Crucible  cast  steel  (plough  *  quality) 240,000 

"  Bright  wire  "  is  that  which  remains  untreated  after  the  last  drawing. 
If  it  is  annealed  or  tempered  in  any  way  after  the  last  drawing,  it  is  left 
black. 

451.  The  Strength  of  Steel- wire  Rope  is  difficult  to  obtain  from  short 
samples  because  of  the  small  stretch  of  the  wires,  and  the  fact  that  some  of 
them  are  more  rigidly  held  than  others.  In  order  to  grip  and  hold  these  ends 
with  equal  effectiveness  various  devices  have  been  tried,  two  of  the  most 
successful  of  which  are  here  described. 

The  first  method  is  to  grip  the  rope  as  a  whole,  without  uncoiling  the 
ends,  by  means  of  grooved  wedges  moving  in  a  steel-plate  holder  as  shown 
in  Fig.  G12.  This  has  worked  successfully  and  requires  no  preparation  of 
the  specimen. 

The  author  has  used  cast-iron  and  steel  holders  having  conical  openings 
for  receiving  the  prepared  ends  of  the  cable  as  shown  in  Fig.  613.  Before 
cutting  off  the  sample  it  should  first  be  bound  tightly  with  soft  wire,  some 
six  inches  from  the  ends,  and  then  cut  off.  The  intervening  length  of 
specimen  should  be  wrapped  tightly  with  tarred  cord  to  hold  the  strands  to 
their  true  position.  The  ends  are  then  inserted  in  the  sockets,  the  strands 
opened  up,  and  each  individual  wire  turned  back  upon  itself  as  shown  at  the 

*  In  Mining  Journal,  June  6 — July  11,  1896. 

t  So  called  because  it  was  first  used  for  drawing  machine-ploughs  in  England  ;  hence 
it  is  now  known  as  "  plough-steel." 


694 


THE  MATERIALS  OF  CONSTRUCTION. 


right  of  the  figure.     The   ends  are  then  boiled  in  caustic   soda  to  remove 
all  grease,  thoroughly  washed  in  hot  water,  and  then  dipped  in  chloride  of 


<S 


C£   O. 


§   *! 

•H 


o 

o 


zinc  and  afterwards  in  molten  solder,  thus  tinning  over  each  bent  wire. 
The  ends  are  then  drawn  into  the  conical  dies  and  an  alloy  of  lead,  tin,  and 
antimony  cast  around  it.*  The  specimens  are  now  ready  to  go  to  the  test- 
ing machine,  where  the  pulling  force  is  applied  to  the  conical  sockets  in 
some  suitable  manner.  Split  steel  sockets,  bolted  together,  may  be  used  if 
preferred.  By  this  means  about  95  per  cent  of  the  combined  strength  of 

*  Tetmajer  uses  8  parts  tin,  1  part  copper,  and  1  part  antimony  for  iron  and  mild- 
steel  wires,  while  for  hard-steel  wires  of  great  strength  he  uses  9  parts  lead,  2  parts  anti- 
mony, and  1  part  bismuth. 


STRENGTH  OF  IRON  AND  STEEL    WIRE,  AND  WIRE  ROPE.      695 


the  individual  wires  can  be  developed  in  the  rope.*  If  the  wedge  grips  can 
be  made  to  give  satisfaction,  however,  they  are  much  to  be  preferred. 

In  long  wire  ropes  on  a  straight  pull  the  strength  of  the  rope  may  be 
taken  as  about  equal  to  the  average  strength  of  the  individual  wires  if  these 
are  all  of  about  the  same  ductility  and  ultimate  strength.  If  the  wires  differ 
greatly  in  ductility,  the  ultimate  strength  of  the  rope  is  the  average  resistance 
of  the  wires  at  that  percentage  of  elongation  which  corresponds  to  the  total 
elongation  of  the  least  ductile  samples.  It  is  common  to  assume  the  rope  to 
have  85  per  cent  of  the  total  strength  of  the  wires  when  tested  individually. 

Wire-rope  pulleys,  sheaves,  and  barrels  should  have  a  diameter  not  less 
than  thirty  times  the  circumference  (or  say  one  hundred  times  the  diameter) 
of  the  ropes  running  upon  them,  to  prevent  excessive  bending  strains  in  the 
ropes. 

In  Table  LIX  are  given  a  summary  of  several  hundred  tests  of  high-grade 
steel  wire  and  of  the  ropes  it  was  made  up  into.  As  these  tests  were  con- 
ducted by  Prof.  Tetmajer  with  great  care,  they  can  be  relied  on  as  giving 
the  facts  for  this  class  of  rope.  The  material  found  in  these  specimens, 
which  were  all  taken  from  ropes  actually  in  service  in  Switzerland,  is  superior 
to  that  usually  found  serving  similar  purposes  in  America.  They  may  be 

TABLE    LIX. — RESUME    OF    TESTS    ON    CRUCIBLE    CAST-STEEL    WIRE    AND 

WIRE    ROPE    USED    ON    CABLE    RAILWAYS    IN    SWITZERLAND. 

(From  Tetmajer' s  Communications,  vol.  iv.  p.  272.) 


Test  of  Entire  Cable.      (Each 
the  Mean  of  Two  Tests.) 

Test  of  Individual  Wires. 
(Each  the  Mean  of  Eleven  Tests.) 

Tension  Test. 

Torsion. 

Bending. 

a  ££ 

o 

Ratio  of 

85 

cc 

«J  «3          I      c  ** 

tw 

54-1       • 

Strength 

Num- 

. 

be 

0 

°.S           - 

of  Cable 

ber  of 

o> 

n 

£-     ^j 

1       -+-£ 

^  a5 

02  NOD 

to  Aver- 

Cable. 

o 

O  0 

PH  3 

~x  ® 

§ 

age 

a 

c 

III 

02 

o 

c  P 

§§  - 

•sa-s 

Is 

^j 

Strength 
of  Wires. 

5 

«w®          Q^s 

•goo 

^    M 

OJ 

a;  a     -2 

043 

p1 

§-3          ooa 

«'H, 

8    ia 

1 

fill 

-    3 

II 

fell 

^1-1,0 

3  to' 

III 

p 

^ 

£ 

72 

PH                       £ 

* 

^ 

1 

1.65 

220,000 

3.12 

265,000 

3.4 

6,400 

27.5 

11.4 

83 

2 

1.67 

117,000 

7.45 

122,000 

9.4 

9,500 

61.5 

11.8 

96 

3 

1.18 

205,000 

2.61 

213,000 

3.0 

4,600 

35.1 

17.8 

96 

4 

1.43 

191,000 

3.30 

207,000 

3.4 

5,000 

44.5 

18.0 

93 

5 

1.00 

184,000 

3.92 

191,000 

3.85 

5.300 

. 

15.1 

96 

6 

1.00 

184,000 

3.28 

190,000 

4.0 

5.700 

52.6 

14.8 

97 

7 

1.38 

180,000 

2.37 

222,000 

3.0 

4,.600 

33.7 

11.0 

77 

8 

1.30 

226,000 

3.00 

247,000 

3.3 

5,700       21.7 

9.6 

92 

9 

1.26 

210,000 

3.15 

238,000 

3.3 

5,400 

31.] 

9.4 

89 

10 

1.00 

190,000 

2.40 

190,000 

2  7 

3,400       48.1 

18.8 

100 

Averages(omit- 
ting  No.  2). 

199,000 

2.98 

217,000 

3.29  i     5,100 

36.8 

14.0 

92 

*  See  article  in  Engineering,  Sept.  11,  1896. 


696 


TEE  MATERIALS  OF  CONSTRUCTION. 


regarded,  therefore,  as  setting  a  pattern  for  American  manufacturers  to 
strive  to  attain  to.* 

It  is  the  opinion  of  the  author  of  this  work,  who  has  had  considerable 
experience  in  testing  high-grade  steel  wire,  that  the  tension  test,  taken  so  as 

to  furnish  a  complete  stress-diagram  (as  Tet- 
majer  took  his),  furnishes  about  all  the 
information  required.  The  percentage  of 
elongation  is  the  best  indication  of  ductility, 
or  pliability,  and  the  area  of  the  stress-dia- 
gram, reduced  to  foot-pounds  of  work  done 
per  cubic  inchxrf  metal  as  in  Table  LIX, 
gives  the  best  indication  of  the  value  of  the 
wire  where  a  very  high  tensile  strength  must 
be  combined  with  as  great  a  toughness  as 
possible.  Next  to  this  comes  the  cold-bend- 
ing test.  The  torsion  test  is,  in  the  opinion 
of  the  author,  of  doubtful  value,  except  that 
it  may  serve  to  indicate  the  uniformity  of 
the  material  by  testing  many  samples.  The 
most  significant  result,  as  indicating  wearing 
quality  or  long  life,  is  the  percentage  of 
elongation  in  the  tension  test.  That  an 
average  strength  of  individual  wires  of 
217,000  Ibs.  per  square  inch  should  be 
coupled  with  an  average  elongation  of  3.29 

per  cent  would  mark  an  unusually  happy  combination  of  strength  and 
toughness,  were  it  not  for  the  fact  that  this  elongation  was  automatically 
recorded,  and  that  it  was  at  rupture  and  not  after  rupture.  The  elastic 
stretch  at  217,000  Ibs.  per  square  inch  would  be  about  0.8  of  one  per  cent, 
so  that  if  this  be  subtracted  we  have  only  2.5  per  cent  elongation  if  meas- 
ured after  rupture.  This  is,  however,  a  high  average  elongation  for  such 
great  strength. 

Fig.  614  shows  an  autographic  stress-diagram  of  a  high-grade  steel  wire 
taken  by  the  author  on  an  English  wire  0.15  in.  diameter,  on  the  machine 
shown  in  Fig.  615.  The  diagram  gives  the  following  results: 

Ultimate  strength  in  pounds  per  square  inch  ..........  =  200,000 


FIG.  614. 


2.5 

4,000 

21 


Percentage  of  elongation  in  48  inches 

Work  of  deformation  in  inch-pounds  per  cubic  inch  ____  = 

Number  of  twists  in  8  in.  (torsion  test)  ...............  = 

Number  of  bends  of  180°  each  on  £  in.  radius  (bending 

test)  .....  .  .....................................  =  3 

*  All  the  instruments  used,  the  methods  employed,  and  the  results  obtained  are  giver 
in  great  detail  in  the  original  volume.  This  volume  (iv)  can  now  be  had  only  in  I 
French  translation. 


STRENGTH  OF  IRON  AND  STEEL    WIRE,  AND    WIRE  ROPE.     697 


By  comparison  with  Table  LIX  \t  is  seen  that  this  wire  is  very  inferior 
to  those  there  recorded. 

The  tension  test  was  made  on  the  machine  shown  in  Fig.  615,  while  the 
bending  test  was  made  on  the  machine  shown  in  Fig.  617. 


c — JSJL L. 


FIG.  615. 
452.  Shop  Tests  of  Wire. — The  most  significant  shop  tests  on  wire  are: 

1.  Tension  tests  with  autographic  stress-diagrams. 

2.  Cold-bending  tests,  through  180°,  back  and  forth  about  jaws  having 
a  radius  of  -J  inch,  or  equal  to  the  diameter  of  the  wire. 

3.  Torsion  tests  on  a  length  of  8  inches  with  self-recording  attachment, 
giving  number  of  revolutions. 

The  instruments  shown  in  Fig.  615  or  GIG  are  very  satisfactory  for  mak- 
ing the  tension  tests.  Both  give  the  record  complete  after  the  specimen  is 
placed  and  the  machine  started,  without  any  personal  attention  whatever. 
In  Fig.  615  the  poise  is  operated  electrically,  while  in  Fig.  616  the  load  is 
indicated  by  the  deformation  of  the  heavy  spring  at  the  top.  This  gives  also- 
the  downward  dip  of  the  diagram  at  rupture  without  any  special  appliances, 
while  in  Fig.  616  this  is  also  done  by  stopping  the  test  and  crossing  a  band 
so  as  to  move  the  poise  backward.* 

The  cold-bending  machine  shown  in  Fig.  617  is  a  very  satisfactory  one. 
By  having  a  number  of  pairs  of  jaws  with  different  radii  these  may  always 
be  made  about  equal  to  the  diameter  of  the  wire.  A  schedule  may  then  be 
prepared  for  the  workman,  instructing  him  to  use  certain  numbers  of  jaws 
with  given  numbers  of  wires. 

The  torsion  tests  are  made  on  a  machine  like  that  shown  in  Fig.  319, 
p.  392.  This,  however,  has  no  revolution-counter  attachment  shown 

*  Some  improvements  have  now  been  introduced  in  this  machine  by  the  maker. 


698  THE  MATERIALS  OF  CONSTRUCTION. 

Other  tests  are  sometimes  resorted  to  to  determine  wearing  quality. 
Thus  Mr.  J   B.  Stone,  C.E.,*  has  arranged  a  series  of  small  pulleys  (about 


FIG.  616. — The  Anisler-Laffon  &  Son  Wire-testing  Machine,  used  by  Prof.  Tetmajer. 
(See  his  Communications,  vol.  iv.  p.  239.) 

G  or  8  inches  in  diameter),  in  such  relative  positions  that  a  wire  drawn  over 
them  is  bent  alternately  in  opposite  directions.  A  given  tension  is  then  put 
on  a  loop  of  wire,  and  it  is  run  over  this  series,  which  is  provided  with  a 

*  Of  the  Washburn  Moen  Works,  at  Worcester,  Mass. 


STRENGTH  OF  IRON  AND  STEEL    WIRE,  AND    WIRE  ROPE. 


revolution-counter,  until  it  breaks.  The  counter  then  gives  the  running 
record  of  the  wire.  Mr.  Stone  then  takes  the  product  of  the  number  of 
revolutions  into  the  tensile  strength  and  calls  this  the  "  hoisting  value"  of 


FIG.  617.— Wire  Setting  for  Cold-bending  Test. 


FIG.  618. — Lang-lay  Wire  Ropfi,  new. 


FIG.  619. — Lang-lay  Wire  Rope,  well  worn. 


FIG.  620.— Ordinary  Lay,  new. 


FIG.  621. — Ordinary  Lay,  well  worn. 

the  wire.  For  comparing  wires  of  the  same  diameter  he  finds  by  experience 
that  this  is  a  good  measure  of  their  true  worth  in  service  when  made  into 
ropes,  and  his  experience  with  this  test  dates  back  to  1882,  when  he  first 


700 


MATERIALS  OF  CONSTRUCTION. 


TABLE    LX. — BREAKING-LOADS    AND     EQUIVALENT    SIZES     AND    WEIGHTS   OP 

WIRE    ROPES. 

(From  J.  Bucknall  Smith's  Articles  011  Wire  Rope  in  Mining  Journal, 
June  6  to  July  11,  1896.) 


Sizes  of  Ropes,  and  Approxi- 
mate Weights  per  Fathom. 

Calcu- 
lated 

Circumference  of  Rope  in  Inches. 

"c 

CO 

<D 

||| 

If1 

Breaking 
Load  of 
Ropes. 

S| 

1 

a 

o> 

|l 

ll 

rcumference 
Rope  in  Inch 

n_i  '«  fe 

O  fl  b 

"a 

W  iT 
«M^3  O 

o.-o  . 

II  ll 

;st  Selected 
tra  Plough  " 
Wire. 

?st  Selected 
"Plough  "-s 
Wire. 

||| 

itent  Crucib 
steel  Wire. 

;st  Selected 
semer-steel  ' 

IS 

18 

Breaking 
Strength 
about 

0 

pE 

t^ 

P3 

PQ 

M 

£ 

M 

M 

Pounds, 

about 

\et  Tons. 

COMPO 

UND    STR 

ANDS 

COMP  OUND  STR 

ANDS 

in 

48" 
44 

42' 

38 

168 
150 
143 

J* 

1 

6% 

::: 

6k 

40 

35 

132 

5^1 

6  4 

6^1j 

.. 

... 

5% 

37 
34 

29 

123 
1  1° 

5 

sfl 

6  4 

5J^ 

30 

26 

J  L~ 

104 

4-M 

5k 

5% 

eii 

5k 

27 

24 

98 

5 

6J4 

5 

25  Via 

23 

95 

4J4 

5}^3 

, 

4% 

24 

22 

90 

4^4 

r>k 

6k 

4^ 

22 

20 

84 

4}4 

5 

6 

6% 

4  4 

\ly2 

16  'J 

78 
73 

4 

4k 

4% 

sft 

6k 

3% 

isk 

i5M 

67 
65 
62 

3£J 

4" 

i 

5" 

6 

5% 

i 

m 

17 

13U 

58 
56 

3^ 

3J6 

4" 

4% 

5J4 

6k 

3^ 

13V»> 

1  1^? 

54 

^l/ 

osx 

.  .  . 

5k 

3% 

12'~ 

i  oi/ 

50 

^3/ 

^5/ 

4Vs> 

5 

6" 

3k 

9 

46 

3k 

glj 

3% 

4k 

4% 

5% 

314 

10  4 

8J4 

43 

3% 

8% 

5V4 

3 

9J/6 

8  " 

40 

3k 

3% 

4 

4/4 

5J4 

2% 

8J4 

7J4 

38 

3" 

"™^"~" 

2% 

8  - 

7 

37 

3/^j 

3^ 

4k 

5 

2^ 

7 

6k 

36 

»  •  • 

3% 

3% 

4% 

2V^ 

6 

35 

2% 

.  .  . 

«  .  • 

296 

51^ 

•5  4  /  1  o 

34 

3" 

3k 

3% 

2J4 

4V  ,o 

82 

2% 

4 

4^ 

2^8 

43/io 

4  4 

30 

2% 

Q1Z 

35^ 

.  .  • 

.  .  • 

2 

4Va 

38/1° 

28 

2% 

3 

3}^ 

3% 

4k 

1% 

4 

26 

2/^ 

2% 

2^ 

3% 

3% 

4 

194 

33/5 

3  i/10 

25 

2% 

3k 

3% 

19o 

2^^ 

24 

296 

1J4 

2J4 

22 

294 

31^ 

jjl^j 

196 

21 

2k 

2^4 

2% 

3 

3% 

ik 

20 

2% 

3% 

3f| 

;*i 

Jk 

19 

2" 

2% 

3k 

3% 

i 

18 

2k 

2^<2 

% 

a/ 

17 

i% 

2V6 

2% 

2% 

31^ 

3V^ 

16 

2 

2k 

2% 

3 

8% 

Sheaves  and  barrels  should  be 

15 
13 

1% 

1% 

2 

2^ 

2M 

3  4 

about  30  times  the  circumfer- 

12                 15^ 

i-M 

JT/ 

296 

2% 

2% 

ence  of  the  ropes  used. 

11 

1*6 

1% 

o 

2% 

NOTE.—  For  shaft-winding  art 
a  high  speed,  one  tenth  of  the 
breaking-strength  of  a  rope  is 
sometimes  taken  as  fair  work- 

10 
9  2 

8  ~ 

196 

!£ 

1 

« 

81 

2*1 

1 

ing-load.     For  inclines,  the  pro- 

ivi 

1% 

1% 

1% 

2k 

portion     of     load  to    breaking 
strength    varies    according    to 
gradient  conditions,  and  friction 
sheuld  be  allowed  for. 

(i 

5  S 

4J4 

* 

i 

iii 

•^ 

1 

1 

4 

... 

1V6 

ik 

196 

iH 

3  2 

i*6 

ik 

_ 

2 
1V*> 

... 

... 

1*6 

1^ 

STRENGTH  OF  IRON  AND  STEEL   WIRE,  AND    WIRE  ROPE.     701 

began  using  it  in  St.  Louis.  This  test  also  indicates  the  uniformity  of  the 
wire.  If,  after  rapture,  it  be  hooked  up  again  and  then  runs  a  considerable 
time  before  breaking,  it  argues  a  weak  spot  in  the  wire  which  caused  the  first 
break.  If,  on  the  contrary,  the  first  rupture  is  quickly  followed  by  others 
on  further  continuance  of  the  test,  it  indicates  that  the  wire  is  uniformly 
worn  out  or  fatigued,  and  that  it  was  very  uniform  in  quality. 

From  examinations  the  author  has  made  on  worn-out  street-railway 
cables,  he  has  reached  the  conclusion  that  the  surfaces  of  contact  with  the 
car-grips  become  highly  heated  immediately  on  the  rubbing-surface,  and  the 
resulting  local  expansion  and  contraction  soon  wears  out  or  fatigues  the 
metal  just  under  these  wearing-surfaces,  thus  causing  the  wires  to  become 
very  brittle  when  bent  with  these  surfaces  on  the  extended  side.  Certainly 
this  extreme  brittleness  exists  at  these  points,  causing  the  outer  wires  to 
become  all  broken  up  into  short  pieces,  as  shown  in  Fig.  621,  before  the  rope 
finally  fails.  A  shop-test  could  probably  be  devised  Avhich  would  determine 
approximately  the  relative  resistance  of  wires  to  this  kind  of  action.  Running 
ropes  of  pulleys  of  too  small  a  radius,  thus  stressing  the  outer  wires  to  or 
beyond  their  elastic  limits  at  every  passage,  would  probably  produce  similar 
results. 

453.  The  Albert-lay  Rope  (commonly  called  Lang-lay*). — By  laying 
up  the  strands  in  the  same  direction  as  the  wires  are  laid  in  the  strand,  the 
rope  presents  the  appearance  shown  in  Fig.  018.,  Any  given  outer  wire 
remains  now  on  the  surface  through  a  much  greater  distance,  and  the  wires 
wear  so  as  to  make  a  rope  almost  as  smooth  as  a  solid  rod,  as  shown  in  Fig. 
619.  Such  a  rope  is  best  suited  to  running  on  or  near  the  ground,  or  where 
there  is  a  large  amount  of  grinding  surface-wear,  as  is  the  case  with  tail-ropes 
in  mines,  with  inclines,  and  with  tramways.  Such  a  lay  makes  a  more 
flexible  rope  also,  and  larger  wires  may  be  used  for  running  over  a  given  size 
of  pulley. 

*  First  used  by  Prof.  Albert,  of  Clausthal,  in  1834.  It  was  patentee!,  however,  by 
Lang  in  1879  and  now  commonly  bears  his  name.  J.  Bucknall  Smith  in  Mining  Journal 
articles,  June  and  July,  1898. 


CHAPTER   XXXIV. 

THE  MAGNETIC  TESTING  OF  IRON  AND  STEEL. 

•» 
By  W.  A.  LAYMAN,  M.S. 

MAGNETIC    PROPERTIES   DEFINED. 

454.  Introductory. — Hardly  less  in  industrial  importance  than  the  accu- 
rate determination  of  the  mechanical  properties  of  iron  and  steel  is  the  care- 
ful   testing   of   their   magnetic   properties.     This   arises   from  the   double 
consideration  of  the  vital  part  played  by  these  properties  and  the  immense 
consumption  of  iron  and  steel  in  what  may  broadly  be  termed  the  electrical 
manufactures.      In  the  construction  of   electric    dynamos,  motors,    trans- 
formers, and  other  forms  of  electrical  machinery,  there  have  gradually  been 
evolved  as  clearly  defined  and  as  rigidly  limiting  requirements  for  iron  and 
steel  along  the  lines  of  magnetic  permeability  and  magnetic  reluctance  or 
hysteresis  as  are  specified  by  the  mechanical  engineer  in  the  directions  of 
elastic  limit,  ultimate  strength,  etc.     These  requirements  are  the  outcome 
of  constant  endeavor  to  lessen  the  cost  of  manufacture  and  increase  the 
operating  efficiency  of  electrical  apparatus.    The  use  for  dynamo-magnets  of 
iron  or  steel  possessing  high  permeability  accomplishes  the  several  good  ends 
of  lessening  size,  weight,  and  magnetizing  energy  required.     The  use  of  iron 
in  transformer  construction  with  low  hysteresis  losses  means  the  same  econ- 
omy in  this  form  of  apparatus.     Accordingly,  iron  manufacturers  as  well  as 
electrical  engineers  are  giving  much  attention  not  only  to  the  testing  of  iron 
and  steel  that  the  magnetic  properties  of  any  given  material  may  be  known 
but  also  to  the  study  of  the  physical  and  chemical  conditions  which  have 
bearing  on  these  properties,  in  order  that  a  scientific  manufacture  of  iron 
and  steel  for  electrical  work  may  be  developed.     Furthermore,  the  necessity 
for  testing  arises  from  another  direction.     The  design  of  electrical  machiner; 
presupposes  definite  magnetic  properties,  in  every  given  case,  of  the  iron  and 
steel  employed.     But  it  does  not  follow  that  the  materials  received  for  us( 
can  be  depended  upon  to  possess  these  qualities.     On  the  contrary,  they  ma} 
vary  between  wide  limits  in  a  given  quantity  which  is  commercially  of  uni 
form  quality.     A  single  casting  of  steel  or  iron  may  vary  greatly  in  differen 
parts.     The  same  is  true  of  wrought  iron,  whether  rolled  in  bars  or  sheets 

702 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL.  703 

Consequently  it  is  vitally  necessary  to  the  successful  fulfilment  of  a  designer's 
predictions  that  his  iron  and  steel  be  thoroughly  and  intelligently  tested. 
Otherwise  his  machine  may  fall  far  short  not  alone  in  operating  efficiency, 
but  in  ability  to  carry  its  rated  load. 

455.  The  Magnetic  Properties  to  be  determined  in  testing,  in  the  case 
of  any  given  specimen  of  iron  or  steel,  are  the  permeability  and  the  hysteresis. 
Permeability  is  expressed  as  a  ratio,  and  is  the  magnetization  per  unit  of 
area,  produced,  divided  by  the  magnetizing  force  producing  it,.  For  mag- 
netizing force  the  conventional  symbol  of  H  is  used,  and  for  magnetization 
the  symbol  B.  Both  are  magnitudes  with  reference  to  unit  area.  In  the 
C.G.S.  system  this  unit  is  the  square  centimeter,  and  in  the  English  system 

•n 

the  square  inch.     Accordingly,  permeability  in  magnitude  is  =.,  and  this 

H 

magnitude  is  symbolized  by  the  Greek  letter  //. 

Imagine  a  soft  iron  bar  closely  wound  from  end  to  end  with  a  magnetiz- 
ing coil  of  insulated  wire,  the  turns  of  which  are  uniformly  distributed  along 
the  bar.  When  an  electric  current  is  sent  through  the  coil  a  condition  of 
magnetization  is  set  up  in  the  bar.  This  condition  is  numerically  expressed 
by  the  number  of  magnetic  lines  of  force  per  unit  area  of  a  section  of  the  bar 
near  its  centre  of  length,  or  as  B.  The  magnetizing  force  is  numerically 
expressed  by  the  number  of  magnetic  lines  of  force  per  unit  of  area  of  the 
enclosed  column  of  air  which  would  take  the  place  of  the  bar  if  it  were 
removed,  or  as  H.  In  other  words,  H  is  the  magnetization  produced  in  air, 
or  B  for  air  is  equal  to  H,  and  JJL  for  air  is  unity.  H  is  determined  by  cal- 
culation from  the  formula 

OATtCN 
H-      -— 


where  A"  is  the  number  of  turns  in  the  magnetizing  coil,  G  the  current  in 
amperes  passing  through  the  coil,  and  L  the  length  of  the  coii  in  inches  if 
H  is  expressed  per  square  inch,  or  in  centimeters  if  H  is  expressed  per  square 
centimeter.  B  is  determined  experimentally.  Permeability  is  not  a  constant 
in  magnitude,  as  will  be  seen  from  a  typical  magnetization  curve  shown  in  (a) 
of  Fig.  622.  For  example,  when  H  is  4,  B  is  8000,  or  ^  is  2000;  but,  when 
H  is  16,  B  is  only  13,000,  or  /<  812.5.  This  means  that  the  magnetization 
can  be  intensified  beyond  a  certain  point  only  at  the  cost  of  a  rapidly  multi- 
plying magnetizing  energy. 

456.  Hysteresis  is  that  property  of  all  forms  of  iron  and  steel  manifesting 
itself  as  a  reluctance  of  the  magnetization  to  follow  changes  in  the  magnetiz- 
ing force.  The  iron  bar  above  may  be  used  to  illustrate.  If  the  bar,  in  its 
original  state,  possessed  no  appreciable  magnetization,  a  constantly  increas- 
ing magnetizing  force  would  produce  a  magnetization  following  the  dotted 
curve  in  Fig.  623  (b).  If  at  the  point  a  the  magnetizing  force  begin  to 
decrease,  pass  through  zero,  and  increase  in  the  negative  direction  to  the 


704 


TEE  MATERIALS  OF  CONSTRUCTION. 


value  of  a  positive,  the  curve  instead  of  returning  on  itself  would  follow  a 
new  path  acd  in  (b)  of  Fig.  622.  If  a  cyclic  operation  be  performed,  the  curve 
of  magnetization  would  become  a  closed  loop  as  in  Fig.  022,  (c).  A  study  of 
this  curve  as  compared  with  the  same  specimen's  magnetization  curve  would 
reveal  a  constant  dragging  of  the  magnetization  behind  the  magnetizing 
force.  This  dragging  when  magnetization  is  periodic  involves  an  expend- 
iture of  energy,  the  enclosed  area  of  the  B-H  loop  as  in  (c)  of  Fig.  622  multi- 
plied by  -  -  numerically  expressing  this  work  in  ergs  per  cubic  centimeter  of 

the  metal  per  cycle.  The  true  cyclic  state  is  not  set  up  at  once,  but  requires 
several  repetitions  of  the  cyclic  operation,  it  having  been  found  that  the 
original  magnetic  intensity  of  #,  Fig.  022,  (c),  is  not  at  first  entirely  re- 


(ft) 


(*) 


'-6  8  ty 


if! 


JL  .A 

&PT 


-a 


CURVE  OF  MAGNETIZATION. 


CURVES  OF  HYSTERESIS. 


FIG,    622.  —  Curves    illustrating    Magnetic    Qualities    of    Iron.      (List.    Civ.   Engrs., 

vol.  cxxvi.) 

stored  at  the  end  of  the  cycle.  It  is  evident  now  that  the  area  of  this 
hysteresis  loop  depends  on  the  intensity  of  magnetization  produced.  In 
other  words,  for  every  maximum  such  as  a  there  will  be  a  definite  B-H 
loop.  It  has  been  experimentally  proved  that  the  locus  of  a  through- 
out the  range  of  magnetization  is  the  magnetization  curve.  This  last 
fact  will  explain  the  practice  hereafter  brought  out  of  obtaining  the 
magnetization  carve  by  subjecting  the  iron  to  reversals  of  magnetizing" 
force  and  taking  half  the  change  of  magnetization  as  equivalent  to  the 
magnetization  which  the  same  force  would  produce  in  a  previously  un- 
magnetized  piece.  Hysteresis  losses  waste  themselves  in  the  production  of 
heat  within  the  material. 

All  kinds  of  iron  and  steel  exhibit  this  property  in  greater  or  less  degree. 
The  softer  the  specimen  of  any  given  material  the  less  in  general  its  hystere- 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL.  705 

sis.  For  transformer  and  armature  work,  accordingly,  it  is  of  prime  impor- 
tance to  carefully  anneal  the  plates  used.  It  may  here  be  asked  why,  in 
work  of  this  class,  thin  plates  are  used.  The  reason  is  that  a  cyclic  current 
not  only  sets  up  a  cyclic  magnetization  in  the  iron,  but  also  an  induced  or 
"  eddy  "  current  in  a  path  parallel  to  that  in  which  the  magnetizing  current 
flows.  The  iron  is  therefore  split  up  in  thin  plates  in  a  transverse  direction 
to  this  flow,  and  the  surface  oxide  of  these  plates,  together  with  the  air-gap 
thus  introduced,  depended  on  to  so  greatly  increase  the  resistance  to  flow  of 
these  "eddy"  currents  that  they  become  of  small  importance,  practically 
confining  themselves  in  length  of  path  to  the  thickness  of  the  plate  alone. 
Plates  for  this  class  of  work  are  rolled  in  thicknesses  varying  between  .014 
and  .035  inch. 

The  effort  has  been  made  to  establish  a  general  law  by  which,  the 
hysteresis  losses  in  any  given  material  at  any  given  magnetic  induction  or 
magnetization  being  known,  the  losses  at  any  other  induction  could  be  cal- 
culated rather  than  determined  experimentally.  Exhaustive  experimental 
results  by  Mr.  C.  P.  Steinmetz  established  the  conclusion  on  his  part  that, 
within  the  limits  of  magnetization  employed  in  general  practical  work,  the 
•energy  loss  by  hysteresis  increases  very  closely  with  the  1.6  power  of  the 
magnetization.  By  means  of  this  fact,  commonly  known  as  Steinmetz's 
Law,  and  the  further  fact  that  the  hysteresis  losses  per  unit  of  time 
increase  in  direct  proportion  with  the  increase  of  rapidity  of  the  cyclic  opera- 
tion, a  reasonably  accurate  calculation  of  the  hysteresis  losses  under  any  set 
of  conditions  may  be  made,  providing  there  is  an  experimental  starting-point 
from  which  to  work. 

METHODS   OF   TESTING. 

457.  Measurement  of  Permeability. — There  are  in  general  four  classes 
of  experimental  methods  of  measuring  permeability: 

(1)  Magnetometric. 

(2)  Balance. 

(3)  Inductive. 

(4)  Traction. 

Of  these  (1)  and  (2)  are  essentially  laboratory  methods.  In  (1)  the 
specimen  is  made  up  as  a  bar,  surrounded  by  a  magnetizing  coil.  B  is 
determined  from  observations  of  the  deflections  produced  by  the  bar  in  a 
magnetometer.  In  ('2)  the  operation  is  in  general  the  same  with  the  excep- 
tion that  a  balancing  magnet  is  used  to  neutralize  the  effect  of  the  specimen 
under  test  on  the  magnetometer.  The  inductive  and  traction  methods  are, 
however,  of  such  character  as  to  permit  of  more  general  application.  These 
may  be  considered  somewhat  in  detail. 

458.  Inductive  Methods. — These  are  based  upon  the  general  principle 
that  an  electric  current  will  be  induced  in  a  given  closed  path  if  that  path 
or  any  part  of  it  is  made  to  sweep  across  a  magnetic  field.     In  addition  to 


706 


THE  MATERIALS  OF  CONSTRUCTION. 


the  magnetizing  coil,  there  is  wound  npon  the  specimen  of  iron  or  steel  a 
small  "  exploring  "  coil.  The  object  sought  in  all  the  forms  is  the  sudden 
removal  of  this  exploring  coil  from  the  magnetic  lines  of  force  embraced  by 
it,  or,  vice  versa,  the  removal  of  the  magnetic  lines  from  the  coil.  This  form 
of  test  is  made  upon  a  specimen  ring  or  long  bar  of  the  iron  or  steel  to  be 
examined.  The  variations  employed  are  all  attempts  to  simplify  the  straight- 
forward and  accurate  form  in  which  the  ring  is  used. 

The  Ring  Method. — In  this  method  the  sample  ring  is  wound  with  a 
primary  or  magnetizing  coil  and  a  secondary  or  exploring  coil,  each  of  a 
known  number  of  turns.  The  general  arrangement  of  apparatus  for  such  a 


FIG.    623. — Arrangement  of  Apparatus  for  Permeability  Testing  by  Ring  Method. 
(Inst.  Civ.  Engrs.,  vol.  cxxvi.) 


test  is  shown  in  Fig.  623.  Here  A  is  the  sample  ring  under  test.  It  may* 
be  either  of  cast  iron,  wrought  iron,  or  steel  as  desired,  of  a  single  piece  in 
thickness  or  of  a  number  of  pieces  according  to  the  requirements.  Prof. 
J.  A.  Ewing,  who  is  general  authority  on  this  subject,  suggests  that  the- 
width  of  the  section  of  the  ring  measured  radially  be  small  as  compared  with* 
the  mean  radius.  He  recommends  an  external  diameter  of  3  or  4  inches, 
with  a  radial  thickness  of  about  J  inch.  B  is  a  storage  cell  for  supplying 
magnetizing  current;  C  a  two-way  switch,  in  one  position  of  which  the  cur-f 
rent  flowing  will  pass  into  the  magnetizing  coil  of  A,  and  in  the  other  into 
the  primary  coil  of  E\  E  is  an  induction-coil,  wound  on  a  non-magnetic 
core,  the  secondary  coil  of  which  corresponds  to  the  secondary  or  exploring 
coil  of  A  and  consists  of  but  a  few  turns  located  near  the  centre  of  the 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL.  707 

primary  winding;  F  is  a  short-circuiting  switch  for  the  D'Arsonval  *  ballistic 
galvanometer,  being  employed  merely  to  bring  the  needle  of  the  galvanom- 
eter to  rest  after  an  observation  has  been  made;  G  is  a  current-meter;  JTa 
reversing  switch  by  means  of  which  the  direction  of  flow  of  current  in  the 
primary  winding  of  A  or  E  may  be  reversed  at  will,  and  also  by  means  of 
which  in  one  position  the  auxiliary  resistance  7?2  may  be  cut  into  circuit  in 
case  the  short-circuiting  switch  S  across  it  is  open. 

This  arrangement  can  be  used  for  determining  either  the  magnetization 
curve  or  the  hysteresis  loop.  The  method  of  procedure  in  the  former  case  is 
as  follows:  A  definite  current,  as  shown  on  (7,  is  passed  from  the  battery 
through  the  primary  coil  of  A,  S  and  F  being  closed.  When  a  general  con- 
dition of  rest  is  established  for  both  G  and  6ra,  by  means  of  K  the  current  is 
several  times  reversed.  On  the  final  reversal  F  is  opened  and  the  swing  of 
6ra  noted.  Half  of  this  swing  is  taken  as  representing  the  magnetization 
produced  by  the  current  read.  The  object  sought  in  the  above  operation  is 
the  complete  removal  of  the  magnetic  lines  of  force  from  the  specimen. 
Were  the  current  not  reversed  in  direction  such  would  not  be  the  case  owing 
to  hysteresis,  and  the  galvanometer  would  only  indicate  the  removal  of  the 
difference  in  magnetic  lines  between  that  produced  by  the  given  current  and 
that  of  the  residual  charge  remaining  after  the  magnetizing  force  has  been 
entirely  removed.  By  reversing  the  current  instead  of  cutting  it  off  the 
whole  magnetic  charge  is  removed  and  at  once  reinserted,  or  the  effect  on 
the  exploring  coil  has  been  equivalent  to  that  of  the  removal  of  twice  the 
maximum  number  of  lines  of  force. 

The  value  of  B  so  determined  is  translated  from  the  scale  of  the  galvan- 
ometer by  standardizing  the  instrument  with  E.  A  given  current  is  sent 
through  the  primary  of  E  and  then  suddenly  cut  off.  The  deflection  on  the 
galvanometer  thereby  resulting,  due  to  a  current  being  generated  in  the 
exploring  coil  of  E,  is  noted.  The  magnetizing  force  H  has  by  this  opera- 
tion been  made  to  record  itself  on  6ra.  H  is  at  once  calculated  by  the  formula 

OAnCN 
above  given  of  H  = =• — ,  N  being  the  number  of  primary  turns  of  E, 

.LJ 

L  the  length  of  E,  and  C  the  current  observed  in  amperes.  From  this  value 
of  H  a  constant  for  the  galvanometer  scale  is  determined.  This  constant  f 

*  This  form  of  galvanometer  consists  of  a  coil  swinging  between  the  poles  of  a  strong 
horseshoe  magnet.  The  swinging  coil  carries  a  mirror,  and  scale  deflections  are  read 
with  a  telescope  in  the  usual  manner.  In  damping,  the  swinging  coil  is  short-circuited 
by  8,  and  the  current  then  generated  in  the  coil  by  the  swing  quickly  brings  it  to  rest, 
f  The  deflection  produced  when  any  test  is  made  whether  on  E  or  A  is  proportional 
to  the  product  of  the  induction  per  unit  of  area  multiplied  by  the  area  multiplied  by 
the  turns  of  the  exploring  coil  multiplied  by  a  constant.  In  the  case  of  two  tests,  one 
on  A  and  one  on  E, 

d     _  H«Y  constant  G 

d"  ~~  Jia"t"  constant  C 

~2 


708  THE  MATERIALS  OF  CONSTRUCTION. 

K,  which  is  the  induction  B  in  the  specimen  ring  for  a  deflection  of  one 
division  on  the  galvanometer  scale  when  a  test  on  A  is  made,  i«  K=  ,,,,,:,„ 

£d    t    CL 

where  //  is  the  induction  per  unit  of  section  of  the  core  of  E,  a!  the  area  of 
the  core  of  E,  t'  the  number  of  turns  in  the  exploring  coil  of  E,  a"  the  sec- 
tional area  of  the  specimen  ring  J,  t"  the  number  of  turns  in  the  exploring 
coil  of  J,  and  d'  the  divisions  deflection  on  6r2  when  the  primary  circuit  of 
E  was  broken. 

The  calibration  of  G9  determined,  the  induction  B  in  a  given  test  on  A 
would  be  the  constant  K  multiplied  by  the  divisions  deflection  shown  on 
the  galvanometer  scale.  H  for  the  magnetizing  coil  of  A  with  any  current 
is  calculated  from  the  formula  for  H  as  given.  The  plotting  of  the  entire 
magnetization  curve  then  but  requires  a  series  of  tests  on  A  alone,  the 
current  being  varied. 

The  Divided-bar  Method. — This  method,  due  to  Dr.  Hopkinson,*  is  an 
attempt  to  secure  the  same  results  as  in  the  ring  method  with  a  much 
cheaper  and  more  easily  made  specimen.  (See  Fig.  624.)  Here  a  heavy  block 
of  annealed  wrought  iron  Fhas  its  central  portion  cut  out  to  receive  a  mag- 
netizing coil  C.  The  test  sample  of  iron  or  steel  SP  is  made  in  two  parts, 
carefully  turned.  These  parts  slide  closely  through  holes  bored  in  the  ends 
of  the  block,  and  the  trued  ends  meet  at  the  exploring  coil  E.  B  is  a  battery 
for  supplying  current,  A  an  ampere-meter,  S  a  reversing  switch,  R  an  adjust- 
able resistance,  and  BG&  ballistic  galvanometer.  In  operation  the  specimen 
rods  are  pushed  tightly  together  and  magnetized  to  any  point  on  the  sought- 
for  magnetization  curve.  Simultaneously  the  circuit  is  now  broken  and 
the  rods  pulled  apart.  The  rods  separated,  a  spring  at  the  same  instant 
pulls  the  exploring  coil  J57  entirely  out  of  the  magnetic  circuit,  The  effect 
is  that  of  the  entire  removal  of  the  lines  of  force  from  the  exploring  coil,  and 
the  whole  deflection  of  BG  is  accordingly  a  measure  cf  the  induction  B  when 
B G  has  been-  properly  calibrated.  Dr.  Hopkinson's  idea  was  to  make  the 
magnetic  resistance  of  the  soft  iron  block  so  small,  as  compared  with  the  rods, 
that  the  condition  of  the  iron  circuit  would  be  very  nearly  the  same  as  if  the 
outside  ends  of  the  rods  were  together.  His  object  in  making  the  specimen 
in  two  pieces  was  to  afford  a  chance  of  getting  the  exploring  coil  out,  other- 
wise the  magnetic  sluggishness  of  the  yoke  would  have  vitiated  the  re- 

"SLa't'd" 

or 


--,-,  =  B  per  scale  division  of  deflection  in  test  on  A  = 

Ha'*' 


In  this  discussion  d'  and  d"  are  deflections  respectively  on  E  and  A,  and  the  factors 
ILa't  refer  to  the  test  on  E,  while  a"t'"B  refer  to  A,  as  above.  The  factor  2  enters  in  by 
reason  of  the  deflection  d"  being  made  as  above  explained. 

*  Phil.  Trans,  p.  456,  1885. 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL. 


709 


suits  of  the  tests.  The  disadvantage  involved  is  the  introduction  of  a  very 
thin  air-gap  where  the  rods  meet  and  also  where  they  pass  through  the  yoke. 
This  introduces  an  error  in  the  calculation  of  the  true  H,  for  it  is  evident 
that  the  magnetizing  current  must  consist  of  four  factors:  (1)  that  required 
to  overcome  the  resistance  of  the  yoke  with  the  given  induction  B  in  the 


ACTION 


FIG.  624. — Hopkinson's  Divided-bar  Method.     (Thompson.) 

rod;  (2)  that  required  to  overcome  the  resistance  of  the  air-gap  between  rods 
and  yoke;  (3)  that  required  to  overcome  the  break  in  the  rods;  and  (4)  that 
required  to  overcome  the  resistance  of  the  rods  themselves.  (1)  may  be 
negligible,  but  (2)  and  (3)  are  not. 

The  Double-bar  'Method. — To  overcome  the  objection  to  Dr.  Hopkinson's 
arrangement,  Prof.  Ewing  has  devised  a  double-bar  double-yoke  method  in 
which  the  errors  involved  in  the  divided-bar  method  can  be  experimentally 
determined  and  allowance  then  made  for  them.  This  is  roughly  illustrated 
in  Fig.  625.  The  specimen  to  be  tested  now  consists  of  two  bars,  magnetized 
in  opposite  directions  and  by  equal  magnetizing  forces,  and  united  by  short 
two-part  yokes  at  each  end.  The  two-part  yokes,  by  means  of  the  clamp- 
screws,  tightly  clamp  the  specimen  bars.  The  test  is  made  in  two  parts. 
First  the  full  length  of  the  bars  is  used,  as  shown  in  part  (a)  of  Fig.  625. 
The  value  of  B  is  determined  ballistically,  and  the  magnetizing  force  H', 
error  included,  calculated.  The  second  test  is  made  with  the  clear  length 
of  the  bars  between  the  yokes  reduced  to  one  half,  and  shorter  coils  used  as 
shown  in  part  (b)  of  the  figure.  Now  the  value  of  the  magnetizing  force 
H"  is  determined  for  the  same  value  of  B  as  found  in  the  first  part  of  the 
test.  The  error  in  the  second  test  is  just  twice  that  involved  in  the  first, 
and  the  correction  it  is  necessary  to  subtract  from  //'  to  give  the  true  mag- 
netizing force  for  the  value  of  B  determined  in  the  first  trial  is  //"  —  //'.* 
*  In  the  first  trial  H Li  —  QAxCiNi  =  HZ,  +  E,  where  H  is  the  true  magnetizing 


710 


THE  MATERIALS  OF  CONSTRUCTION. 


The  Magnetic  Bridge  Method. — With  the  object  in  view  of  still  further 
facilitating  and  simplifying  permeability  testing  to  meet  workshop  require- 
ments, Prof.  Ewing  has  devised  another  very  neat  method  which  he  calls  the 
' ' magnetic  bridge. ' '  The  principle  involved  in  this  method  is  the  production 


a 


FIG.  625. — Ewing's  Double-bar  Permeability  Method.     (Inst.  Civ.  Engrs.,  vol.  cxxvi.) 

of  a  magnetic  balance,  so  to  speak,  between  a  test  specimen  and  a  standard 
specimen,  the  exact  permeability  curve  of  the  latter  having  been  previously 
determined  by  the  two-yoke  ballistic  method  above.  The  process  is  analogous 
to  resistance  measurements  with  the  Wheatstone  bridge,  hence  Prof.  Ewing's 
suggested  name  of  the  magnetic  bridge.  The  arrangement  is  illustrated  in 
Fig.  626.  The  two  bars,  one  the  test  specimen  and  the  other  the  standard, 
are  #,  a.  Connecting  these  bars  at  their  ends  are  heavy  yokes  of  soft  iron 
W ,  made  in  the  form  of  rings  and  held  in  place  by  three  longitudinal  brass 
rod&fff.  A  cross  yoke  of  soft  iron  gg,  with  a  central  break  in  it  at  7^,  is 
carried  up  above  the  end  yokes.  In  the  gap  h  a  detector-needle  is  inserted, 
this  being  directed  by  an  adjustable  magnet  k  on  a  brass  rod  below  it.  The 


force,  Ci  the  current  read,  Ni  the  turns,  L,  the  clear  length  of  the  specimen  bars,  and 
Eilie  error  introduced  by  the  joint  with  the  yokes  and  the  yoke  resistance. 

In  the  second  trial  //  'L2  =  0.4^(7,^  =  H£2  -f  E,  where  Z2,  <72,  and  N*  have 
corresponding  values.  Since  B  i^  the  same  in  both  trials,  H  is  also  the  same.  For  this 
reason  E  is  the  same  in  both  cases. 


From  the  above 


and 


..  i    •    i       mi 

from  which  H" 


n/,_ 
**    — 


JL 
Z7 

E_ 
L, 


0.47TCWV3 


E 


TT,  _   E       H_  _  2E 

"~    T  ~T~  ~~    T  / 

X/a         -L*i        -*ji         -"i 


Accordingly,  H  =  IT  -    -  =  II'  -  (H"  -  H'). 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL. 


711 


bars  aa  are  enclosed  by  magnetizing  coils  wound  on  brass  spools.  These 
coils  are  so  arranged  with  switching  devices  that  fractional  parts  of  them 
may  be  cut  in  or  out  of  circuit  at  will.  The  test  consists  in  sending  a  given 
current  into  these  coils  connected  in  series.  If  the  magnetizations  produced 
in  the  bars  are  equal,  there  will  be  no  difference  in  magnetic  potential 
between  the  yokes  lib'.  But  if  the  magnetizations  are  unequal,  there  will  be 


s 


I, 


1  J 


> 


FIG.  626. — Ewing's  Magnetic  Bridge.     (Inst.  Civ.  Engrs.,  vol.  cxxvi.) 

a  difference  in  magnetic  potential  between  b  and  #',  and  this  will  manifest 
itself  by  endeavoring  to  relieve  itself  across  the  soft  bar  g,  thereby  producing 
a  deflection  of  the  detector-needle.  The  magnetizing  turns  over  the  two 
bars  aa  are  now  so  adjusted  with  reference  to  each  other  that,  on  reversal  of 
the  current,  no  permanent  displacement  of  the  detector-needle  is  observed. 
The  ratio  of  the  two  magnetizing  forces  is  then  the  ratio  of  the  number  of 
effective  turns  employed.  B  for  the  standard  bar  is  taken  from  a  table 
accompanying  it,  the  ampere-turns  of  magnetization  being  known.  The 
permeability  for  either  bar  is  easily  calculated.  It  is  here  assumed  that  the 
measured  magnetizing  forces  are  in  the  same  ratio  as  the  real  forces,  an 
assumption  which  involves  no  appreciable  error. 

The  idea  of  comparing  permeabilities  in  the  two  arms  of  a  magnetic  cir- 
cuit is  not  new,*  but  Prof.  Ewing  is  'the  first  to  employ  this  adaptation.  The 
only  trouble  that  seems  to  have  been  experienced  in  using  this  device  is  a 
"  kick  "  on  the  part  of  the  detector-needle  arising  from  different  periods  of 
time  required  for  the  magnetizations  in  the  standard  and  specimen  bars  to 
establish  themselves. 

The  Voltmeter  Method.— This  method,  as  illustrated  in  Fig.  627,  has 
been  used  by  Prof.  W.  E.  Ayrton.  The  specimen  to  be  tested  is  made  up 
as  a  bar  and  slipped  into  the  heavy  pole-pieces,  a  magnetizing  coil  wound  on 
a  bobbin  sliding  over  it  between  the  poles.  A  small  armature  revolves 

*  Trans.  Amer.  Inst.  Elec.  Eng.t  vol.  LX.  p,  3. 


712 


THE  MATERIALS  OF  CONSTRUCTION. 


between  the  poles  at  a  constant  speed,  this  armature  being  driven  by  a 
small  motor.  When  the  specimen  is  magnetized,  the  armature  generates  an 
electric  current  which  flows  through  the  voltmeter.  This  current  is  directl} 
proportional  to  the  induction  in  the  bar.  From  the  ammeter-reading  the 
magnetizing  force  H  is  known,  and  from  the  voltmeter- reading  the  indue* 


FIG.  627.— Ayrton's  Voltmeter  Method.     (Inst.  Cm.  Engrs.,  vol.  cxxvi.) 
tion  B  is  determined  by  comparisons  made  with  a  standard  bar  employed 
under  exactly  the  same  conditions  as  to  magnetizing  force  and  speed.     The 
(magnetic  curve  of  this  standard  bar  has  been  previouslv  determined  by  a 
ballistic  method. 

459.  Traction  Methods. — These  methods  are  based  on  the  fact  that  when 
magnetic  induction  crosses,  through  surface-faces  in  close  contact,  from  one 
magnetized  body  to  another,  these  bodies  resist  being 
pulled  apart.  The  amount  of  this  resistance  or  "  trac- 
tive force  "  is  dependent  on  the  intensity  of  the  induc- 
tion. The  traction  methods  are  all  directed  to  the 
simplifying  of  induction  measurements.  Of  them  all, 
perhaps  the  best  known  and  most  generally  used  is  Prof. 
S.  P.  Thompson's  "Permeameter"  method.  This  is 
illustrated  in  Fig.  628.  In  general  the  apparatus  closely 
resembles  Dr.  Hopkinson's  divided-bar  arrangement. 
There  is  the  same  heavy  yoke  and  a  single  magnetizing 
coil.  The  change  is  largely  in  the  test-specimen,  which 
is  now  made  as  a  single  rod,  carefully  faced  on  the 
lower  end  where  it  makes  close  contact  against  the  yoke. 
When  a  current  is  sent  through  the  magnetizing  coil, 
the  rod  sticks  tightly  to  the  yoke  at  its  lower  end.  This 
tractive  force  is  measured  upon  the  spring-balance  in 
pounds  pull  required  to  separate  the  rod  from  the  yoke. 
B  is  deduced  from  the  formula  B  =  1317  V~P  ~  A  -f  H, 
where  A  is  the  area  of  contact  of  the  rod  upon  the  yoke, 
and  P  the  pull  in  pounds.  H  is  here  added  for  the 
FIG.  628.  —  Thomp-  reason  that  the  magnetizing  coil  is  not  moved  with  the 
rod,  as  a  consequence  of  which  the  pull  is  that  due  to 


son's  Permeameter. 
(Thompson.) 


B  —  H  lines. 


The  Magnetic  Balance. — -This  device,  due  to  Dr.   II.  du  Bois,  is  illus- 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL.  713 

trated  in  Fig.  629.-  The  yoke,  as  will  be  seen,  is  divided,  the  tipper  portion 
being  supported  on  knife-edges  in  such  a  way  that  an  air-gap  of  definite 
width  is  introduced  between  portions  of  the  yoke.  The  test-bar  is  inserted 
between  the  lower  detached  ends  of  the  yoke.  The  test  is  made  by  moving 
the  sliding  weights  until  the  rocking  part  of  the  yoke  is  pulled  away  from 


SO      70        .BO" 


FIG.  629. — Du  Bois  Magnetic  Balance.     (Inst.  Civ.  Engrs.,  vol.  cxxvi.) 


the  small  stop  which  determines  the  air-gap.  A  curve  is  furnished  by  the 
maker  of  the  apparatus  for  correcting  H  to  compensate  for  the  errors  intro- 
duced by  the  air-gap. 

460.  Measurement  of  Hysteresis. — In  the  measurement  of  hysteresis 
losses  a  great  variety  of  methods  have  been  used.  In  general  these  have 
aimed  at  simplicity  and  facility  of  testing  rather  than  accuracy.  As  a  result 
they  have  been  more  nearly  relative  than  absolute  methods.  Some  have  been 
based  on  the  fact  that  the  hysteresis  losses  waste  themselves  in  the  produc- 
tion of  heat  within  the  iron.  In  such  devices  there  is  always  liable  to  be  a 
great  inaccuracy  arising  from  the  complication  of  heat  being  also  produced 
by  the  eddy  currents  which  a  cyclic  magnetizing  current  will  set  up  If  the 
test-specimen  is  made  of  very  thin  plates,  and  if  the  reversals  of  magnetizing 
currents  are  not  too  rapid,  this  error  may  be  largely  eliminated. 

Another  series  of  methods  involves  the  use  of  an  electric  wattmeter. 
Here  the  specimen  usually  takes  the  form  of  a  closed  magnetic  circuit,  wound 
with  a  strong  magnetizing  coil  into  which  an  alternating  current  is  sent. 
By  means  of  the  wattmeter  the  total  energy  consumed  in  producing  the 
magnetization  is  observed.  Here,  again,  however,  the  complication  of  eddy 
currents  enters,  as  also  a  loss  of  energy  due  to  the  resistance  of  the  wire. 
This  method  is  nevertheless  a  very  common  one  in  workshops  where  a  sys- 
tematic and  strictly  scientific  study  of  materials  has  not  been  entered  into. 
By  means  of  an  exploring  coil  to  which  a  voltmeter  is  attached  the  induction 
B  is  known.  In  the  hands  of  a  man  who  understands  thoroughly  the  use  of 
electrical  instruments,  and  who  also  has  a  knowledge  of  the  relations  existing 
between  power,  pressure,  and  current  in  a  circuit  carrying  an  alternating 
current,  a  wattmeter  method  will  afford  no  small  degree  of  satisfactory  ser- 
vice. But  in  the  hands  of  a  less  able  man  it  is  of  little  value. 

The  Ring  Method. — All  other  methods  failing,  there  remains  the  straight- 
forward ballistic  or  ring  method  shovvn  in  Fig.  623  and  by  which  perme- 


714  THE  MATERIALS  OF  CONSTRUCTION. 

ability  testing  was  illustrated.  For  the  plotting  of  tli3  accurate  hysteresis 
curve  the  general  method  of  procedure  is  but  slightly  changed.  The  first 
step  is  to  determine  accurately  the  maximum  point  a  of  the  loop,  Fig.  622 
(c).  This  is  done  exactly  as  the  corresponding  point  on  the  magnetization 
curve  in  Fig.  622  (a)  would  be  found.  After  a  has  been  determined,  the 
switch  A" being  on  the  proper  side  to  permit  it,  the  magnetizing  current  for 
a  is  suddenly  reduced  by  any  desired  amount  by  simply  opening  the  switch 
8  and  thereby  cutting  in  72a.  The  magnetization  drops  in  magnitude  as 
does  the  current,  but  not  so  far.  The  full  swing  of  the  galvanometer  meas- 
ures its  change.  This  would  determine  a  single  point  between  a  and  c,  Fig. 
622  (c),  dependent  on  R^  for  its  position.  Then  A"  is  switched  over  to  the 
other  side,  giving  again  the  full  current  of  «,  but  reversed  in  sign  and  now  the 
negative  current  of  d.  Next  7?2  is  changed  in  value,  and  then,  with  S  still 
open,  A"  is  switched  again.  The  current  becomes  positive  in  direction,  but 
decreased  from  the  magnitude  of  d  by  an  amount  depending  on  R^.  The 
swing  of  the  galvanometer  this  time  determines  a  point  somewhere  between 
a  and  d.  Closing  S,  the  magnetization  runs  back  again  to  «,  and  everything 
is  in  readiness  for  another  cycle.  Thus,  with  each  cycle,  two  points  on  the 
loop  are  found,  one  between  a  and  c,  and  the  other  between  e  and  a.  As  the 
curve  is  symmetrical,  ac  is  also  de,  and  ea  also  dc.  Thus  the  full  curve  is 
established. 

Ewincfs  Hysteresis-tester. — Prof.  J.  A.  Ewing  has  recently  brought 
forward  an  extremely  simple  machine  for  direct  measurement  of  hysteresis 
which  he  calls  a  "  hysteresis-tester."  This  is  illustrated  in  Fig.  630.  The 
sample  of  iron  which  is  to  be  tested  by  comparison  with  a  standard  sample 
is  prepared  by  piling  about  half  a  dozen  3  X  g-inch  stampings  or  strips  of 
the  iron  sheet  into  a  bundle,  and  clamping  the  same  between  vulcanite 
washers  by  the  clamps  bb  on  the  carrier  a. 

This  carrier  is  made  to  revolve  by  means  of  d  between  the  poles  of  a 
strong  permanent  magnet  e,  which  magnet  is  hang  on  knife-edges  in  line 
with  the  axis  of  the  carrier  so  that  it  may  swing  in  a  concentric  arc  with  the 
carrier  a.  .  The  magnet  is  given  some  stability  by  a  small  weight  g.  Below 
e  is  a  small  cup  in  which  a  suspended  vane  swings  in  oil,  thus  providing  a 
dash-pot. 

The  principle  involved  is  that  the  hysteresis  gives  rise  to  a  mechanical 
couple  between  the  sample  and  the  magnet,  this  couple  tending  to  pull  the 
magnet  around  in  a  circle  after  the  revolving  specimen.  A  deflection  from 
a  vertical  plane  results,  which  deflection  is  indicated  on  a  scale  at  the  top  of  • 
the  supporting  post  of  e.  This  deflection  is  a  measure  of  the  hysteresis. 
With  reference  to  the  operation  of  the  instrument  Prof.  Ewing  says:  "  The 
deflection  is  independent  of  the  speed  (so  long  as  that  is  not  so  high  as  to 
cause  supplementary  deflection  by  air-currents),  and  hence  no  particular 
care  has  to  be  taken  to  turn  the  handle  at  a  uniform  rate.  The  operator 
has  merely  to  turn  the  handle  just  fast  enough  to  make  the  impulses  which 
are  given  at  each  half-revolution  blend  into  a  steady  deflection.  The  deflec- 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL 


715 


tion  is  observed  first  to  one  side  and  then  to  the  other  by  reversing  the 
direction  of  rotation."  A  considerable  air-space  is  left  between  the  ends  of 
the  sample  and  the  magnet-poles  for  the  purpose  of  putting  practically  all 
of  the  resistance  of  the  magnetic  circuit  in  these  gaps,  and  consequently 
eliminating  the  permeability  of  the  specimen  as  a  factor.  The  induction 
used  in  testing  is  about  four  thousand  lines  per  square  centimeter.  Prof. 


FIG.  630.— Swing's  Hysteresis  Tester.      (Inst.  Civ.  E/tgrs.,  vol.  cxxvi.) 

Ewing  has  found  that  no  exact  adjustment  of  the  section  of  the  sample  is 
necessary,  it  being  sufficient  to  take  that  number  of  strips  which  come  nearest 
in  weight  to  the  standard  sample  which  is  furnished  with  the  instrument. 
"  A  small  error  is  involved,  probably  due  to  the  fact  that  there  is  some 
hysteresis  in  the  magnet  itself  when  the  sample  is  revolving." 

The  objection  to  the  instrument  is  that  tests  can  only  be  made  at  a  single 
induction.  To  this  objection  Prof.  Ewing  has  replied  that  Steinmetz's  Law, 
within  the  range  of  inductions  usually  obtaining,  affords  easy  translation  to 
any  induction  desired.  All  in  all  the  instrument  is  certainly  a  valuable 
addition  to  the  magnetic  testing  apparatus  now  at  command. 


716 


THE  MATERIALS  OF  CONSTRUCTION. 


RESULTS   OF   TESTS 

461.  Development  Due  to  Testing. — Magnetic  tests  have  established 
relationships  between  the  various  forms  of  iron  and  steel  manufactured,  which 
are  depicted  in  the  typical  curves  of  magnetization  and  hysteresis  presented 
in  Figs.  631  to  635  inclusive.  These  curves  are  worthy  of  close  study,  as 
from  them  may  be  read  not  only  the  characteristic  magnetic  differences 
between  the  various  forms  of  steel  and  iron,  but  also  the  story  of  many  radi- 
cal changes  that  have  quickly  succeeded  each  other  in  the  manufacture  of 
electrical  machinery.  Fig.  631  alone,  for  example,  will  explain  why  the 


40       60       SO       100       /20      140      160 
FIG.  631. — Characteristic  Magnetization  Curves. 


I&O      200 


generating  dynamo  of  to-day,  with  only  from  one  half  to  three  quarters  the 
volume  of  magnetic  material  in  it,  is  equal  in  electrical  capacity  to  the 
dynamos  of  ten  years  ago.  This  fact  is  evident  from  the  magnetic  superi- 
ority of  cast  steel  over  cast  iron.  In  the  early  manufacture  of  dynamos  and 
motors,  the  field-magnets  and  connecting  yokes  were  made  entirely  of  cast 
iron.  The  magnetic  superiority  of  wrought  iron  was  soon  more  generally 
appreciated,  and  pole-pieces  were  then  forged,  where  manufacturing  facili- 
ties permitted.  This  was  a  distinct  gain,  but  as  a  considerable  part  of  the 
magnetic  circuit  was  still  of  cast  iron  because  all  parts  of  the  dynamo 
frame,  for  mechanical  reasons,  could  not  be  forged,  much  was  still  to  be 
desired  from  the  standpoint  of  magnetic  economy.  Forged  steel,  having  no 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL. 


717 


magnetic  advantage  over  wrought  iron,  afforded  no  improvement.  Cast 
steel,  however,  developing  practically  as  high  permeability  as  either  wrought 
iron  or  forged  steel,  except  with  very  weak  magnetizing  forces,  at  once 
accomplished  the  great  advantage  sought.  The  entire  framework,  pole- 
pieces  and  yokes  included,  could  be  easily  cast,  and  the  result  has  been  the 
adoption,  where  facilities  permit,  of  cast  steel  for  all  forms  of  electrical 
machinery  calling  for  solid  rather  than  "laminated  parts.  Within  the  last 
two  years  a  still  further  improved  form  of  dynamo-magnet  construction  has 
been  introduced,  mention  of  which  only  can  be  made  here.  This  is  the 
building  up  of  the  magnetic  polar  projections  of  the  field-frame  of  laminated 
wrought  iron  or  steel.  These  poles  are  then  placed  in  their  proper  relative 
positions  in  the  mould  for  the  field-frame,  and  the  cast  steel  for  the  remain- 
ing parts  poured  around  them.  The  object  sought  is  the  elimination  of  the 
eddy  currents,  which  are  induced  in  the  pole-faces  when  the  machine  is  in 
operation. 

Fig.  632  will  especially  make  clear  why  there  is  such  a  marked  superiority 


FIG.  632.— Curves  showing  Relative  Hysteresis  Quality  of  Three  Specimens.     (Inst.  Civ. 

Engrs.  vol.  cxxvi.) 

of  one  alternating-current  transformer  over  another  of  the  same  general 
dimensions,  a  fact  generally  known  but  not  generally  understood.  In  this 
figure  are  given  the  hysteresis  curves  of  three  different  makes  of  iron 
furnished  for  the  same  class  of  work.  The  tests  were  made  by  Prof.  Ewing. 
XIV  was  furnished  as  soft  wrought  iron,  but  the  curve  discredits  this  claim. 
It  will  be  seen  that  XII  is  vastly  superior  to  XIII,  while  XIV  as  compared 
with  either  XII  or  XIII  is  exceedingly  poor.  Fig.  G35  still  further  em- 


718  THE  MATERIALS  OF  CONSTRUCTION. 

phasizes  how  marked  may  be  the  differences  between  materials,  under  a- 
cyclic  magnetization,  all  supposed  to  be  commercially  suitable  for  the  same 
class  of  work.  Here  are  given  both  magnetization  and  hysteresis  curves,  the 
results  being  taken  from  a  recent  paper  by  Prof .  Ewing.*  lisa  special 
grade  of  Swedish  transformer  iron,  from  which  Prof.  Ewing  makes  the 
standard  bars  used  with  his  hysteresis-tester;  II  is  a  transformer-plate  of 
steel;  III,  another  quality  of  Swetfish  transformer  iron;  IV,  a  transformer- 
plate  made  from  scrap-iron;  and  V,  a  specimen  of  iron  wire  used  by  Mr. 
Swinburne  some  years  ago  in  the  manufacture  of  his  "hedgehog"  trans- 
former. From  these  curves  is  further  evident  the  cause  of  much  of  the 
great  improvement  that  has  been  made  in  the  efficiency  of  all  forms  of 
apparatus  where  hysteresis  is  involved. 

462.  Conditions  Affecting  Magnetic  Quality. — Careful  testing  has  fur- 
nished much  information  as  to  the  conditions  which  affect  the  magnetic 
quality  of  iron  and  steel.  Of  these  conditions,  which  may  in  general  be 
classed  as  physical,  great  magnetic  differences  in  materials  are  sometimes 
due.  For  example,  permeability  is  seriously  affected  by  such  operations  as 
hammering,  rolling,  etc.  A  given  specimen  of  soft  annealed  iron  may  have 
its  permeability  greatly  reduced  by  the  hardening  resulting  from  stretching. 
In  the  same  way,  steel,  hard  drawn,  has  much  lower  permeability  than  steel 
annealed.  With  cast  metal  the  suddenness  of  cooling,  in  similar  manner, 
seriously  affects  the  magnetic  quality.  Material  under  excessive  strain  also 
has  its  permeability  lowered.  As  a  general  rule,  the  warmer  the  metal  the 
lower  its  permeability.  That  the  hysteresis-factor  is  also  seriously  affected 
by  many  of  these  same  conditions  is  more  generally  appreciated.  Hence 
the  electrical  manufacturer's  effort  to  carefully  anneal  his  iron. 

The  part  played  by  chemical  composition  is  not  so  well  understood.  The 
fact  of  the  matter  is  that  as  yet  the  study  of  magnetic  quality  from  the 
standpoint  of  chemical  composition  has  not  been  systematically  or  exhaus- 
tively entered  into.  But  few  results  of  value  in  this  direction  are  at  com- 
mand. Accordingly,  a  recent  paper  by  Mr.  II.  F.  Parshall  f  is  of  unusual 
value,  as  it  contains  results  of  a  great  many  tests  in  which  chemical  composi- 
tion was  very  closely  considered.  Mr.  Parshall  calls  attention  to  the  fact,  as. 
brought  out  in  his  results,  that,  "  beginning  with  the  most  impure  cast  iron 
and  passing  thiough  the  several  grades  of  cast  iron,  steel,  and  wrought  iron, 
the  magnetic  properties  accord  principally  with  the  amounts  of  carbon 
present,  and  in  a  lesser  degree  with  the  properties  of  sulphur,  phosphorus, 
manganese,  and  other  less  usual  ingredients;  and  that  an  excess  of  any  one' 
or  of  the  sum  of  all  the  ingredients  (other  than  iron)  has  a  noticeable  effect 
on  the  magnetic  properties."  Fig.  634  is  here  produced  from  Mr.  Parsh all's  • 
results  to  support  his  conclusions,  as  also  to  indicate  the  general  magnetic  • 
qualities  of  the  materials  tested.  In  this  direction  it  may  be  stated  as  ai 

*  Proc.  Inst.  Civil  Engrs.,  vol.  cxxvi.  p.  184. 
f  Proc.  Inst.  Civii  Eng.,  vol.  cxxvi.  p.  220. 


THE  MAGNETIC  TESTING   OF  IUON  AND  STEEL. 


719 


generally  observed  fact  that  the  purer  the  iron  the  higher  the  permeability. 
Results  of  tests  by  Prof.   Ewing  in  curves  II,   III,  and  IV  of  Fig.  G33, 


I 


FXCEP, 


H  L 


M 

IF 


CAS 


20        30 


BAR 


MG-0', 


40 


L  (roz  D 


WEALEO) 


YMAMO 


CAffBON 

S/L/COM 


SULPHU 


?  ao/3 


MA0A/E, 


TffACE 
TfiACE 
A/0.V£ 


&METS) 
•s) 


FIG.  633. — Magnetization   Curves  showing  Relation  between  Wrought  Iron  and  Steel. 


/  ,.          OWdffA/   fWOS.       SM/CO/V  M/IA/6 

'  Ji  CASTOrtfL  &230  0.057  d/95  0.48B  #.042  0  A 006 

JF    „        „    0337  0.077  33/g  0.74280380  /.592 

0.0SO  0./9G  O.MS  0.//3  ft 707 


V        /#        20        30       40        60        60        70  ft  60 

FIG.  634. — Parshall's  Results  showing  Effect  of  Impurities  on  Magnetization. 

ilthough  the  chemical  compositions  are  not  given,  may  be  said  to  bear  out 
:his  fact. 

With,  reference  to  hysteresis  loss  in  laminated  iron,  there  has  recently 
3een  shown  to  exist  in  many  qualities  of  material  a  gradual  deterioration 
mder  the  conditions  imposed  by  continued  service.  Of  such  a  striking 


720 


THE  MATERIALS  OF  CONSTRUCTION. 


nature  is  this  change  that  much  attention  is  being  paid  to  it.  Cases  are. on 
record  in  which  the  hysteresis  losses  in  transformers  under  heavy  service  hav 
increased  over  100  per  cent.  Mr.  Parshall  cites  one  case  in  which,  during 
two  years'  service,  the  increase  was  about  200  per  cent.  Many  observation; 
bearing  on  this  property  of  iron  and  steel  are  given  by  Mr.  Parshall.  Hi. 
tests  covered  six  months'  service,  in  general,  of  the  samples  of  material  unde 
examination.  The  magnetic  induction  was  closely  the  same  in  all  speci 
mens,  while  the  temperature  of  service  varied.  Several  specimens  gave  n< 
evidence  of  change  whatsoever.  Others  changed  as  much  as  25  per  cent 
Chemical  analysis  only  indicated  a  difference  in  the  percentage  of  silicoi 
present,  but  whether  the  change  is  related  to  or  dependent  on  the  silicoi 
cannot  now  be  positively  stated.  Taking  this  change  of  quality  into 
account,  it  may  be  seen  that  the  manufacturer  of  transformers  has  two  con 


B 


z 


'fit'S IS  LOSS 


0      2       d       6       &       /O      /2      14      16      /8 

FIG.  635. — Ewing's  Results  on  Transformer  Iron  and  Steel. 

siderations  involved  in  the  selection  of  his  iron  or  steel  plate.  First,  tl 
quality  of  material  with  reference  to  permeability  and  hysteresis,  and  secon 
the  quality  of  material  with  reference  to  permanency  of  magnetic  propertii 
under  continued  service.  It  is  possible  for  the  change  in  quality  to  tal 
from  materials  greatly  superior,  on  first  examination,  all  of  the  superior! 
possessed  by  them.  More  data  are  badly  needed  upon  this  phase  of  tl 
subject. 

463.   In  Conclusion  the  reader  is  again  invited  to  closely  study  all  t) 


THE  MAGNETIC  TESTING   OF  IRON  AND  STEEL. 


721 


curves  presented.  They  are  plotted  from  accurate  and  authentic  tests,  and 
show  not  alone  the  relative  qualities  and  absolute  magnetic  values  of  the 
various  forms  of  steel  and  iron,  but  also  many  elements  which  the  special 
needs  of  the  investigator  may  lead  him  to  search  for.  Furthermore,  the 
data  are  almost  entirely  new,  which  gives  a  still  greater  value. 

It  is  also  desired  to  place  great  emphasis  on  the  need  as  well  as  desir- 
ability of  thorough,  accurate,  and  continued  magnetic  testing  of  materials. 

TABLE   LXI.— USEFUL   DATA   ON   ELECTRICAL   CONDUCTIVITY,  ETC. 


Electrical  Conductivity. 

Specific  Gravity. 

Specific  Heat.  Average 
at  Ordinary  Tempera- 
ture. (Regnault.) 

1 
$ 

Q 
^n 

£ 

h 

il 
1* 

Coefficient  of  Thermal 
Conductivity.  (Wie- 
|  demanu  and  Franz.) 

At  Normal  Tem- 
peratures. 
(Lezare  Weiler.) 

Mathi 

cS 

d* 

£8 
—  ~ 
<u<! 

*ssen. 

ol 

II 

+3  -U 
<*4 

Pure  silver  

100 
100 
99.9 

98.0 
86.65 
78.0 
75.0 
54.7 
54  2 

100 

71.56 

10.505 

8.853 

19.258 
2.67 

7.00 

7.35 
21.5 

11.38 
8.8 

2.67 
13.58 

0.0570 
0.0951 

0.0324 
0.2185 

0.0956 

0.0562 
0.0324 

0.0314 
0.10863 

0.0508 
0.0333 

1733  to  1873 
1929  to  1996 

1913  to  2285 
1157     -j 

680  to   779 

442  to   446 
3227 

608  to   618 
810toll50-j 

100 
73.6 

53.3 

37.96 
to 

38.87 

14.5 

8.4 

8.5 

19.2* 
to 
21.5 
67.7* 

Pure  copper  , 

Refined  und  crystallized  copper. 
Telegraphic  silicious  bronze  
Alloy  of  copper  and  silver  (50$). 
Pure  gold                 . 

99.95 
77.96 

70.27 
55.90 

Silicide  of  copper  4$  Si  

Silicide  of  copper,  12$  Si  

Tin  with  12$  of  sodium  .... 

46.9 
35.0 
30.0 
29.9 
29.0 
26.49 
21.5 
17.7 
16.12 
16.0 
15.45 
12.7 
12.6 
12.0 
10.6 
10.6 
10.2 
10.14 
9.1 
8.88 
8.4 
7.89 
6.50 
4.90 
3.88 

29.02 

12.36 
18.00 

8.32 

20.67 

8.67 

Telephonic  silicious  bronze.  .  .  .  . 
Copper  with  10$  of  lead  

Pure  zinc  

Telephonic  phosphor-bronze.  .  . 
Silicious  brass  25$  zinc  

Brass   35$  zinc 

Phosphor-tin 

Alloy  of  gold  and  silver  (50$)  .  .  . 

Pure  Banca  tin  

Antimonial  copper.  .    .          . 

Aluminum  bronze  (10$)  

.Siemens  steel  

Pure  platinum 

Copper  with  10$  of  nickel 

5.86 

Cadmium  amalgam  (15$).  .  .  . 

Dronier  mercurial  bronze  

Arsenical  copper  (10$) 

Pure  lead  

Bronze  with  20%  of  tin  

Pure  nickel  

Phosphor-bronze,  10$  tin 

4.62 
1  60 

3.26 

Phosphor-copper,  9$  phosphor.  .  . 
Antimony  

Mercury  

*  Calvert  &  Johnson. 


722  TEE  MATERIALS  OF  CONSTRUCTION. 

On  the  scientist's  part  this  necessity  is  fully  appreciated,  for  he  understands 
that  just  as  the  present  knowledge  of  their  magnetic  properties  and  the  suc- 
cessful use  of  iron  and  steel  in  the  electrical  manufactures  is  the  result  oi 
careful  testing,  so  also  is  future  development  along  these  lines  dependent  OK 
testing.     On  the  manufacturer's  part  there  is  a  constantly  growing  appre- 
ciation of  the  great  advantages  to  be  gained  from  testing.     The  electrical 
manufacturer,  knowing  how  great  may  be  the  variation  in  magnetic  quality 
of  the  materials  furnished  him,  is  keenly  alive  to  the  fact  that  he  cannot 
maintain  nor  advance  the  standard  of  his  apparatus  without  testing.     The 
iron  and  steel  manufacturer,  in  turn,  is  coming  to  see  that  he  cannot  much 
longer  furnish  for  electrical  work  such  materials  as  are  included  in  his  regular 
line  of  manufacture.     Electrical  work  is  beginning  to  demand  rather  than  ( 
accept,  and  soon  must  have  materials  which  are  shown  by  scientific  study  to  I 
best  meet  the  requirements  of  this  department  of  industry.     The  situation  j 
is  one  in  which  the  consumer  must  not  only  protect  himself,  but  lend  all  the  i 
assistance  within  his  power  to  the  scientific  study  of  magnetic  phenomena, ? 
while  the  iron  manufacturer  must,  by  the  limitations  of  trade  competition, 
know  from  his  own  investigations  the  quality  of  the  materials  he  is  turning 
out  and  the  part  played  by  physical  and  chemical  conditions  of  manufac- 
ture.    From  every  point  of  view  is  clearly  evident  the  importance  of  the 
magnetic  testing  of  iron  and  steel. 


APPENDIX  A. 

A  BIOGRAPHICAL  SKETCH  OF  THE  LIFE  OF  PROFESSOR  JOHAKN" 

BAUSCHINGER.* 

PROFESSOR  BAUSCHINGER  was  born  in  Niirnburg  in  1834.  His  father  was  an 
artisan,  and  had  a  large  family.  Young  Bauschinger,  therefore,  at  an  early  age 
saw  the  earnest  side  of  life,  and  he  learned  to  have  faith  in  his  ability  to  support 
himself.  At  the  age  of  fourteen  he  began  giving  private  lessons.  However,  gifted 
with  a  strong  will-power,  he  completed  the  course  at  the  Polytechnic  School  with 
honors  in  1853  at  the  same  time  receiving  his  certificate  from  the  Latin  School. 
Having  selected  mathematics  and  physics  as  the  branches  which  he  desired  eventually 
to  teach,  he  studied  for  three  years  at  the  University  of  Munich.  Under  von  Lamont 
he  studied  with  great  enthusiasm  theoretical  and  practical  astronomy.  He  had  the 
rare  opportunity  of  using  the  astronomical  and  magnetic  instruments  in  the  royal 
observatory  at  Bogenhausen.  Here  he  developed  that  faculty  of  keen  observation 
and  learned  the  scientific  methods  of  discussing  and  reducing  observations  to  obtain 
the  most  probable  results,  which  afterward  stood  him  in  such  good  stead. 

In  the  fall  of  1856,  after  having  passed  the  examinations  for  teacher  in  mathe- 
matics and  physics,  he  accepted  the  position  as  assistant  in  physics  and  descriptive 
geometry  at  the  Polytechnic  School  in  Augsburg,  and  in  1857  he  was  called  to 
Fiirth,  where  he  became  teacher  of  mathematics  and  physics  at  the  Royal  Industrial 
School. 

In  1866  Bauschinger  was  transferred  to  the  Academy  in  Munich,  and  two  years 
later  he  became  professor  there  of  mechanical  engineering  at  the  newly-founded 
Technical  School.  In  1870  he  became  director  of  the  testing  laboratory,  which  was 
built  under  his  direction  and  according  to  his  plans.  Here  he  remained  and  labored 
in  the  interest  of  science  until  his  death. 

At  Fiirth  Bauschinger  had  already  developed  a  literary  activity.  Papers  by  him 
on  subjects  pertaining  to  mechanical  engineering  and  thermodynamics  appeared  in 
various  publications.  As  an  independent  work  he  published  his  popularly-written 
School  of  Mechanics.  This  was  followed  in  1871  by  The  Elements  of  Graphical 
Statics. 

Without  doubt  Bauschinger's  best  and  most  valuable  publications  were  those 
relative  to  his  physical  tests.  His  Indicator  Trials  on  Locomotives  had  been  begun 
as  early  as  1865,  and  they  were  continued  at  Munich  under  extreme  difficulties  on 
; account  of  the  great  amount  of  work  he  was  called  on  to  perform  as  professor  in 
the  Technical  School.  However,  Bauschinger's  main  field  of  investigation  was  in 
|he  testing  of  materials.  Here  he  earned  great  and  indisputable  fame. 

His  writings  since  1871,  published  in  the  Journal  of  the  Society  of  Bavarian 
Architects  and  Engineers  and  other  publications,  and  later  in  his  Communications 
from  the  Testing  Laboratory  of  the  School  of  Technology  of  Munich,  will  long  fur- 
nish ample  data  for  the  study  of  the  strength  of  materials.  His  was  the  first  public 
testing  laboratory  in  all  Germany,  and  it  has  continued  to  stand  as  the  most  noted 
in  the  world  in  many  respects.  This  institution,  with  its  furnishings,  has  served  as 
a  model  for  all  later  similar  establishments. 

*  Compiled  by  the  author  from  a  more  extended  memoir  by  Prof.  A.  Martens,  and  published  in  the 
Digest  of  Physical  Tests  for  July,  1896. 

723 


724  APPENDIX. 

Bauschinger  greatly  improved  our  means  for  testing  materials  by  the  invention 
of  accurate  measuring  apparatus,  one  example  of  which  was  his  application  of  the 
Gauss  method  of  mirror  readings,  by  which  all  measurements  are  very  accurately 
obtained.  Many  other  accurate  measuring  and  testing  devices,  now  commonly 
employed,  are  due  to  him. 

Referring  now  to  his  contributions  to  the  science  of  the  strength  of  materials,  in 
his  "  Communications"  we  may  say,  in  short,  that  in  the  numbers  1,  4,  5,  7,  8,  10, 
11,  18,  and  19  he  treats  of  the  strength  of  cements,  mortars,  and  artificial  and  nat- 
ural building-stones.  In  numbers  1,  7,  and  8  Bauschinger  speaks  of  his  numerous 
tests  of  cements,  and  cement  and  lime  mortars.  In  these,  as  well  as  in  the  tests 
of  artificial  and  natural  stones  discussed  in  numbers  4,  5,  10,  and  11,  18,  and  19, 
different  methods  were  used,  and  the  various  results  were  compared.  He  has  made 
a  special  study  of  the  elasticity  and  strength  of  building-stones.  At  the  same  time 
and  in  the  most  detailed  manner  he  made  cross-bending,  tension,  compression,  and 
shearing  tests  of  the  same  materials. 

For  the  investigation  of  the  wearing  of  stones  an  abrasion  method  was  devised 
(see  Art.  436,  p.  645).  The  effects  of  freezing  are  minutely  examined  and  compared, 
and  many  simplifications  are  given  to  the  conscientious  worker. 

In  No.  6  of  the  "Communications  "  are  treated  the  laws  of  compression.  Besides 
discussing  the  older  works  of  the  French  and  English,  his  own  experiments  are  given. 
In  other  numbers,  2,  3,  13,  20,  and  21,  the  properties  of  metals,  the  law  of  the 
resisting  power  of  iron  and  stone  columns  in  fire  (numbers  12  and  15),  and  the 
methods  of  testing  to  determine  the  mechanical  properties  of  wood  (numbers  9  and 
16),  etc.,  are  discussed.  The  change  of  the  elastic  limit  and  strength  of  iron  and  steel 
due  to  stretching  and  crushing  is  especially  to  be  noticed  (number  13). 

The  "  Conventions  for  the  Agreement  as  to  the  Methods  of  Testing  Building  and 
Construction  Material,"  of  which  he  was  president,  were  entirely  due  to  his  ener- 
getic action.  The  reports  of  these  meetings  are  contained  in  numbers  14  and  22  of 
Ms  "Communications,"  the  latter  of  which  he  did  not  live  to  complete.  These 
conventions  led  directly  to  the  permanent  International  Association  which  has  since 
been  organized. 

His  work  was  recognized  in  all  parts  of  the  world.  He  was  made  member  of  the 
Royal  Prussian  Academy  of  Architects,  also  of  the  Royal  Bavarian  Academy  of 
Science  in  Munich  and  of  the  Imperial  Academy  of  Naturalists  at  Halle  ;  also  honor- 
ary member  of  the  American  Society  of  Mechanical  Engineers,  of  the  Royal  Im- 
perial Technological  Industrial  Museum  in  Vienna,  and  of  the  Royal  Bavarian 
Industrial  Museum  in  Niirnburg,  etc.,  etc. 

He  died  on  the  25th  of  November,  1893,  after  having  given  the  scientific  world 
the  results  of  his  experiments,  his  theories,  and  his  improvements  in  testing- 
machinery,  which  will  ever  stand  as  an  indestructible  monument  to  his  memory. 


APPENDIX   B. 

STUDY  OF  IRON  AND  STEEL  BY  MICROGRAPHIO  ANALYSIS. 
By  Prof.  J.   O.  ARNOLD,  Sheffield,  Eng. 

I.  POPULAR.* 

THE  ever-increasing  severity  of  engineers'  specifications,  framed  to  secure  trust- 
worthy qualities  in  metals  used  for  structural  purposes,  has  undoubtedly  had  the 
effect  of  stimulating  metallurgists  to  make  closer  scientific  investigations,  having 
for  their  object  the  determination  of  the  fundamental  laws  governing  the  chemical 
physics  of  metallic  alloys,  and  the  exact  working  of  those. laws  with  reference  to  the 
ultimate  mechanical  properties  of  metals.  More  particularly  in  connection  with 
iron  and  steel,  the  fact  is  now  generally  recognized  that  materials  identical  in 
chemical  composition  may  possess  widely  different  mechanical  properties.  When 
the  observations  of  the  analytical  chemist,  although  indispensable,  nevertheless 
became  of  more  limited  value,  the  metallurgical  physicist  appeared  on  the  scene 
and,  it  must  be  confessed,  very  ably  put  forward  a  theory  that  the  otherwise  inex- 
plicable differences  in  the  practical  properties  of  chemically  identical  masses  of  iron 
or  steel  must  be  due  to  allotropic  changes  in  the  iron  itself,  and,  for  a  time,  allo- 
tropic  molecules  became  fashionable.  When,  however,  practical  metallurgists  found 
that  the  allotropic  school  put  forward  as  part  of  their  belief  the  startling  creed  that 
chromium  and  tungsten,  silicon,  sulphur,  and  phosphorus  soften  steel,  it  became 
evident  that,  as  far  as  the  practical  applications  were  concerned,  there  was  a  rift  in 
the  theoretical  lute,  arid  that  the  indication,  furnished  by  some  other  line  of  re- 
search were  destined  to  explain  the  puzzling  effects  frequently  observed. 

During  the  last  few  years  it  lias  become  more  and  more  apparent  that  the  veil 
would  only  be  lifted  from  the  mysteries  of  metals  by  micrographic  analysis — a  fact 
of  peculiar  interest  and  encouragement  to  young  experimenters  starting  along  the 
thorny  path  of  research.  Young  scientists,  after  executing  and  publishing  patient 
and  valuable  work,  will  often  find  that  their  efforts  are  received  with  indifference. 
Such  investigators  should  remember  that  the  micrographic  analysis  of  iron  and 
steel  was  inaugurated  thirty-five  years  ago  by  Dr.  Sorby,  in  a  research  which,  for 
patience  of  execution  and  sterling  value  of  results  achieved,  has  seldom  been  ex- 
celled. The  sagacity  of  Dr.  Sorby's  preconceived  idea,  that  metals  should  be  re- 
garded as  crystallized  igneous  rocks,  is  -now  generally  recognized.  Nevertheless 
practical  metallurgists  have  only  quite  recently  realized  that  Sorby's  research 
founded  the  science  of  metallography.  This  science  is  destined  in  the  near  future 
to  become  an  indispensable  adjunct  to  chemical  analysis,  and  it  has  already  practi- 
cally proved  that  the  metallurgical  engineer,  instead  of  groping  for  the  causes  of 
abnormal  mechanical  effects  in  the  outer  darkness  of  molecular  metaphysics,  may 
often  readily  find  such  causes  well  within  the  range  of  actual  vision  by  means  of  a 
cheap  microscope. 

In  a  word,  the  venue  of  trial  has  been  changed  from  molecules  to  crystals,  or,  to 
be  more  strictly  accurate,  from  molecular  to  intercrystalline  cohesion,  or,  it  may  be, 
adhesion.  The  magnitude  of  this  change  is  hardly  capable  of  mental  realization, 
but  its  enormity  may  be  vaguely  grasped  by  recalling  Lord  Kelvin's  calculation  of 

*From  Iron  and  Coal  Trades  Review,  1896. 

725 


726  APPENDIX, 

the  probable  approximate  dimensions  of  a  molecule,  namely,  that  if  a  single  dro 
of  water  be  magnified  up  to  the  size  of  the  earth,  the  constituent  molecules  of  th 
drop  would  be  somewhere  about  the  size  of  marbles.  It  is  encouraging  to  kno\ 
that  the  growing  importance  of  micrographic  analysis  has  become  a  matter  o 
international  recognition,  and  among  patient  investigators  engaged  in  its  develop 
ment  in  America,  England,  France,  Germany,  and  Holland  may  be  mentioned  th< 
names,  respectively,  of  Stead,  Osmond,  Martens,  and  Behrens.  There  is  little  doub 
that  the  efforts  of  these  and  other  workers  will  soon  raise  metallography  to  the  rani 
of  a  definite  science,  but  the  path  of  the  student  seems  likely  to  be  rendered  neces 
sarily  difficult  by  the  assignation  of  names  to  apocryphal  constituents,  and  tin 
curse  of  synonyms  already  hovers  over  the  science. 

Many  people  are  inclined  to  associate  the  microscopic  examination  of  steel  witl 
a  grave*  peering  into  fractures  with  a  hand  lens.  It  is  well  to  clearly  understanc 
once  and  for  all  that  the  fracture  of  a  piece  of  steel  or  iron  has  but  little  correla 
tion  with  its  ultimate  structure.  The  latter  is  ascertained,  firstly,  by  obtaining  i 
perfectly  polished  section  of  the  metal;  secondly,  by  delicately  etching  with  .acic 
the  prepared  surface,  in  order  to  reveal  the  constituents,  just  as  the  structure  of  t 
macadamized  road  is  revealed  after  a  heavy  flush  of  rain.  The  results  so  far  ob 
tained  by  this  method  of  examination  have  proved  that  even  a  chemically  pure 
metal  is  not  a  homogeneous  solid,  being  built  up  of  a  number  of  primary  metallic 
crystals,  which  may  themselves  break  up  into  a  large  number  of  secondary  crystals. 
It  is  extremely  probable  that  the  mechanical  properties  of  such  a  metal  are  measured, 
not  by  molecular  cohesion — not  even  by  the  cohesion  between  the  secondary  crys- 
tals—but by  the  attractive  force  acting  between  the  facets  and  the  large  primarj 
crystals. 

Passing  on  to  the  question  of  the  so-called  alloys,  the  indications  of  the  micro 
scope  have  already  gone  far  to  negative  the  generally  accepted  idea  that  an  alloj 
consists  of  a  homogeneous  solution  of  one  metal  in  another,  or  of  a  non-metallic 
element  in  a  metal.  To  take  the  specific  case  of  steel  in  its  ordinary  state,  as 
used  for  structural  purposes,  the  microscope  has  forever  removed  from  the  mine 
of  the  engineer  any  idea  that  he  has  to  deal  with  a  homogeneous  mass.  To  bring 
steel  into  its  purest  and  essential  form,  in  which  iron  and  carbon  are  the  mair 
constituents,  the  microscope  has  proved  that  steel  is  grown  from  iron  by  gradual!} 
increasing  the  carbon  present,  and  that  it  reaches  maturity,  otherwise  a  compara- 
tively homogeneous  mass  of  true  steel,  when  the  percentage  of  carbon  approximates 
0.9  per  cent.  This  percentage  constitutes  the  critical  microscopical  point  of  steel, 
and  has  been  named  the  "saturation-point."  The  addition  of  more  carbon  pro- 
duces a  supersaturated  steel,  slowly  progressing  towards  pig  iron.  However, 
structural  engineers  are  more  immediately  concerned  with  unsaturated  steels — that 
is  to  say,  steel  containing  less  than  0  9  per  cent  of  carbon.  In  such  material,  what 
may  be  called  a  semi-critical  point  of  great  importance,  from  an  engineer's  view,  is 
presented  in  iron  containing  0.45  per  cent  of  carbon.  The  material  then  consists  oi 
an  intimate  mixture  of  perfectly  distinct  crystals  of  iron,  and  of  true  steel  contain- 
ing 0.9  per  cent  of  carbon,  in  equal  proportions.  This  metal  presents  mechanical 
properties  intermediate  between  those  of  pure  iron  and  true  steel.  Should  an  engi- 
neer in  his  specification  demand  a  carbon  higher  than  "0.45  per  cent,  he  will  obtain  a 
material  possessing  the  characteristics  of  steel  rather  than  those  of  iron.  On  the* 
other  hand,  in  metals  containing  less  than  0.45  per  cent  of  carbon  the  character- 
istics of  iron  will  predominate.  The  above  statements  have  reference  to  an  idea!- 
case,  the  consideration  of  which  is,  however,  absolutely  necessary  to  form  the  base- 
line of  steel  metallurgy.  In  practice  the  case  becomes  complicated  because  of  the 
presence  in  structural  steels  of  from  0.5  per  cent  to  1  per  cent  of  manganese.  The 
influence  of  the  quantity  last  named  on  the  mechanical  properties  of  steel  is  wel 
known,  and  its  effect  on  the  microscopic  structure  is  remarkable.  Nevertheless,  ii 
seems  to  have  escaped  the  observation  of  most  steel  microscopists.  There  is  little 
doubt  that  the  observed  effects  are  due  to  the  formation  of  a  remarkable  triple 
compound  of  iron,  manganese  and  carbon. 

Our  knowledge  of  this  subject  is  far  from  complete  ;  it  is,  in  fact,  a  branch  o: 
the  subject  requiring  immediate  and  rigorous  investigation.  It  is,  however,  certair 
that  in  iron  containing  1  per  cent  of  manganese  the  microscopic  saturation-poin 


STUDY  OF  IRON  AND  STEEL  BY  M1CROGRAPHIC  ANALYSIS.   727 

marking  the  conversion  of  the  iron  into  a  homogeneous  compound,  steel,  appears 
about  0.65  per  cent  of  carbon.  We  have  in  this  fact  a  satisfactory  explanation 
of  the  well-known  mechanical  differences  between  Swedish  and  English  Bessemer 
spring-steel  of  like  carbon,  the  kinder  properties  of  the  Swedish  material  being  due 
to  the  fact  that  it  contains  only  about  J  per  cent  of  manganese.  Further  investiga- 
tions, not  yet  ripe  for  publication,  have  gone  far  to  indicate  that  the  specific  action 
of  the  elements  nickel,  chromium,  tungsten,  and  silicon  are  due,  not  to  the  ele- 
ments per  se,  but  to  a  remarkable  series  of  double  carbides  of  the  respective  elements 
with  iron.  The  substances  above  mentioned  are,  however,  often  useful  when  em- 
ployed to  obtain  the  mechanical  properties  demanded  by  unusually  severe  specifi- 
cations. But  the  steel  metallurgist  is  confronted  by  the  invariable  presence  of  two 
elements,  the  action  of  which  is  always  injurious,  frequently  to  an  extent  seemingly 
out  of  all  proportion  to  the  percentages  present.  Speaking  broadly,  sulphur  is  the 
more  deadly  enemy,  for  reasons  which  open  up  a  wide  field  of  research  in  general 
metallurgy.  The  cause  of  the  more  injurious  action  of  sulphur  may  be  stated  in  a 
word.  Sulphide  of  iron,  which  (and  not  sulphur)  is  the  substance  writh  which  the 
engineer  has  to  reckon,  is  far  more  fusible  than  phosphide  of  iron.  The  extent  to 
which  mass  fragility  may  be  produced  by  very  small  quantities  of  a  fluid  or  semi-fluid 
f constituent,  after  the  main  mass  of  the  material  has  solidified,  is  hardly  capable  of 
exaggeration,  and  microscopical  evidence  will  presently  be  published  which  will 
•conclusively  prove  that  proportions  of  sulphur  hitherto  deemed  harmless  may,  under 
certain  conditions,  produce  a  remarkable  mass  weakness  fully  capable  of  account- 
ing for  mysterious  and  disastrous  effects.  Sulphide  of  iron  is  incapable  of  adherence 
to  the  constituents  adjacent  to  it  within  the  mass,  so  that  the  extent  of  its  injurious 
effects  will  depend  upon  the  form  in  which  it  exists  mechanically.  Its  least  in- 
jurious form  is  that  of  fused  globules,  which  are  practically  equivalent  to  minute 
blowholes.  Its  most  dangerous  form  is  that  of  attenuated  membranes  enveloping 
groups  of  crystals,  and  forming  long  lines  of  weakness  equivalent  to  minute  cracks. 
The  mechanical  distribution  of  the  semi-fluid  sulphide  during  the  rolling  and  ham- 
mering of  steel  presents  dangerous  possibilities  and  requires  rigorous  microscopical 
investigation. 

A  fruitful  field  of  research  which  has  already  yielded  important  results  is  the 
microscopical  determination  of  the  changes  taking  place  during  annealing.  The 
constituents  chiefly  involved  in  this  change  are  the  carbides  and  sulphides,  and  the 
results  already  obtained  have  completely  negatived  the  accuracy  of  the  generally 
accepted  theory  of  annealing.  It  is  not  intended  in  the  present  article  to  antici- 
pate, by  premature  publication,  the  remarkable  influence  of  annealing  on  the  distri- 
bution of  sulphide  of  iron,  and  the  increase  in  mechanical  strength  following  such 
redistribution.  With  reference  to  carbides,  however,  it  may  be  pointed  out  that  in 
one  of  our  leading  text-books  on  metallurgy  the  toughening  influence  of  the  process 
of  annealing  is  attributed  to  three  causes  :  1.  A  change  of  hardening  qarboninto  car- 
bide carbon.  2.  A  breaking  up  of  large  crystals  into  minute  crystals.  3.  A  distribu- 
tion of  carbide  carbon  from  crystalline  pellets  into  finely-diffused  particles.  Micro- 
graphic  analysis  has  shown  that  not  only  are  the  foregoing  statements  inaccurate, 
but  they  are  also  opposed  to  fact,  for  the  following  reasons  :  1.  There  is  no  harden- 
.ug  carbon  in  steel  castings.  2.  The  crystals  become  much  larger  on  annealing. 
3.  The  carbide  carbon  is  entirely  concentrated  into  crystalline  pellets.  The  above 
case  is  a  single  example  of  the  light  destined  to  be  thrown  on  the  metallurgy  of 
steel  by  micrographic  analysis.  It,  however,  yet  remains  for  engineers  to  fully 
grasp  the  realities  briefly  set  forth  in  this  article.  To  do  so  it  is  necessary  to 
examine  a  comprehensive  collection  of  properly  prepared  iron  and  steel  micro- 
sections.*  The  recognition  of  the  value  of  the  science  to  metallurgical  engineers  has 
undoubtedly  been  retarded  by  a  pedantic  adherence  to  the  reproduction  of  the  struc- 
tures observed  by  photography. 

It  seems  that  the  idea  that  the  camera  is  the  George  Washington  of  inanimate 
life  has  not  yet  been  exploded.  As  a  matter  of  fact,  there  is  only  one  philosophical 
instrument  capable  of  conveying  more  inaccurate  impressions  than  the  camera,  and 
that  is  the  gas-meter.  Any  one  who  is  familiar  with  the  actual  structures  of  steel, 

*  See  Plates  IX  and  X. 


728  APPENDIX. 

and  with  the  foggy  series  of  photographs  published  from  time  to  time  to  represent 
them,  will  admit  the  accuracy  of  the  above  statement.  The  technical  difficulties  in- 
volved in  photographically  reproducing  the  micro-structure  of  opaque  objects  under 
high  powers  are  so  great,  that  at  present  the  only  reliable  means  of  reproduction  is 
laborious  hand-drawing,  employing  either  a  micrometer  or  camera  lucida  ;  and  the 
only  reasonable  objection  to  such  a  course  is  an  imputation  of  mala  fides  to  the 
operator. 

For  obvious  reasons,  the  structure  of  iron  and  steel  has  herein  received  most 
attention;  micrographic  analysis  is  capable,  however,  of  application  to  many  alloys, 
and  of  explaining  not  only  their  mechanical  properties,  but  also  their  electrical  con- 
ductivities, so  that  the  science  is  of  importance,  not  only  in  practical  metallurgy, 
but  also  iu  theoretical  physics,  based  on  observations  of  the  electrical  properties  of 
alloys. 

II.  TECHNICAL.* 

The  study  of  this  very  important  branch  of  steel  metallurgy,  initiated  thirty  years 
ago  by  Dr.  Sorby,  has  attracted  considerable  attention  on  the  Continent.  In  Ger- 
many, particularly,  great  strides  have  been  made  in  its  development  under  the 
superintendence  of  Professor  Martens.  By  English  metallurgists  it  has  been  until 
quite  recently  almost  neglected,  or  condemned  with  faint  praise.  The  mechanical  dif- 
ficulties of  preparing  a  perfect  section  and  of  delicately  etching  the  surface,  so  as  to 
reveal  its  true  structure  when  examined  with  high  powers  as  an  opaque  object,  are  con- 
siderable. The  author  has  only  overcome  these  obstacles  after  some  years  of  laborious, 
experiment,  for  which,  however,  he  has  been  amply  repaid  by  the  discovery  that  the 
laws  determining  the  structure  of  iron  containing  various  percentages  of  carbo-n 
are  fixed  and  concordant  for  given  physical  conditions;  in  fact,  from  puzzling  chaos 
he  has  been  enabled  to  evolve  order  of  a  most  interesting  character,  supplying,  more- 
over, the  key  to  the  position  he  was  attacking. 

The  Constituents  of  Iron  and  Carbon  Steels. 

Pure  Iron. — Perfectly  pure  iron  is  never  mot  with  in  commercial  masses,  but  in 
Swedish  Lancashire  hearth-rolled  bars,  containing  in  their  average  analysis  99.8  per 
cent  of  iron,  groups  of  almost  chemically  pure  crystals  of  the  metal  may  be  met  with. 
They  are  readily  distinguished  by  their  well-defined  facets  and  angles,  and  by  the 
fact  that  tiiey  remain  bright  and  smooth  even  after  prolonged  attacks  by  the  exces- 
sively dilute  nitric  acid  used  for  etching,  which  merely  penetrates  and  makes  visible 
the  fine  junction-lines  of  the  crystals.  In  Fig.  636  is  shown  a  micrometric  reproduc- 
tion of  crystals  of  pure  iron  viewed  by  direct  illumination  and  magnified  600  diame- 
ters. Their  geometric  form  agrees  most  nearly  with  that  produced  by  interfering 
cubes  and  octahedra  with  dominant  cubic  faces.t  It  is,  however,  unusual  to  meet 
with  such  well-defined  and  geometrical  crystals  as  those  figured,  because  of  the  dis- 
tortion-stresses taking  place  in  the  metal  during  cooling  after  crystallization,  which 
phenomenon  the  author's  experiments  J  indicate  as  occurring  at  a  moderate  red 
heat,  the  formation  commencing  at  750°  C.  and  being  completed  at  720°  C. 

Slightly  Impure  Iron. — In  wrought  iron  and  in  mild  steels  the  free  iron  crystals 
are  often  somewhat  contaminated  with  a  little  residual  carbon,  which  causes  them; 
during  the  process  of  etching  to  assume  a  pale-brown  tint  and  a  rough  surface.  The 
amount  of  carbon  so  involved  is  very  small,  seldom  exceeding  0.05  per  cent,  and  its 
mechanical  influence  is  insensible.  The  author,  therefore,  will  not  at  present; 
further  discriminate  between  the  two  kinds  of  iron  crystals,  though  the  exact  nature 
of  the  carbide  existing  in  the  tinted  crystals  has  some  molecular  interest  in  connec- 
tion with  Osmond's  point  AR  3.  When  very  mild  steels  are  submitted  to  prolonged 
heating  in  a  vacuum  at  a  temperature  of  1400°  C.  and  are  then  cooled  in  air, 
the  microstructure  of  the  steels  undergoes  a  distinct  change,  in  which  the  knots  of' 


*  From  List.  Civ.  Engrx.,  vol.  cxxm.  (1896),  p.  137  et  seq. 

t  In  a  recent  communication  to  the  Royal  Society  Mr.  Thomas  Andrews,  F.R.S.,  has  shown  that 
in  heavy  slowly -cooling  masses  of  wrought  iron  the  large  primary  crystals  often  split  into  numerous 
secondary  cubes. 

t  Journal  of  the  Iron  and  Steel  Institute,  1894.  No.  1,  p.  132  et  seq. 


STUDY  OF  IRON  AND  STEEL  BY  MICROGRAPHIC  ANALYSIS-   729 

normal  carbide  of  iron  disappear  and  a  large  increase  takes  place  in  the  number  of 
tinted  crystals.  These  facts  are  correlated  thermally  with  a  large  permanent  increase 
in  the  heat  evolved  at  AR  3  on  cooling,  the  carbon  change-point  almost  disappearing 
at  AR  1  and  its  position  at  AR  3  being  raised  about  10°  C.  These  results  are  consis- 


.  636.— Pure  Irou  Crystals  Magnified  600  diameters. 


tent  with  the  theory  that  there  may  exist  traces  of  a  carbide  of  iron  intermediate  in 
formula  between  the  normal  carbide  Fe3C,  and  the  all-important  subcarbide  to  be 
tpiregently  described. 

rwffitsed  Normal  Carbide* — These  areas,  when  the  polished  section  is  immersed 
•hi  very  dilute  nitric  acid,  are  at  once  partly  covered  with  a  dark-brown  film  of  car- 
bonaceous coloring  matter,  the  latter  thus  constituting  an  invaluable  automatic 
staining  medium.  The  dark  areas,  as  wTill  be  shown  subsequently,  consist  of  iron 
containing  about  13  per  cent  of  normal  carbide,  Fe3C,  diffused  through  its  substance 
in  the  form  of  small,  ill-defined  plates  and  granules.  They  also  mark  the  preliminary 
stage  of  formation  of  the  ''pearly  constituent." 

The  Pearly  Constituent. — This  constituent  is  best  developed  in  annealed  steels, 
and  presents  the  well-known  hard  and  soft  laminae  discovered  by  Dr.  Sorby.  It  has 
already  been  shown  that  the  hard  laminae  are  crystals  of  Fe3C.  The  soft  interspaces 
are  nearly  pure  iron.  The  parallel  carbide  plates  may  be  wavy  or  straight,  and  they 
differ  much  in  thickness  and  their  distances  apart.  When  the  iron  interspaces  are 
very  wide,  the  carbide  plates  are  distinctly  seen  to  be  in  relief,  the  fibres  of  the  pol- 
ishing blocks  having  excavated  the  soft  iron.  Sections  containing  much  "pearly  con- 
stituent "  present  on  etching  a  beautiful  play  of  pearly  or  opaline  interference  colors, 
which,  if  the  etching  is  very  light,  are  permanent. 

Crystallized  Normal  Carbide  (Fe3C).— This  substance,  exclusive  of  its  occurrence 
in  the  pearly  constituent,  may  gather  into  large  sectional  rivers  or  into  isolated 
masses.  It  requires  then  an  experienced  eye  to  distinguish  it  from  perfectly  pure 
iron,  but,  as  a  rule,  the  fact  that  it  is  always  in  relief  and  its  brilliant  silvery  surface 
serve  to  identify  it. 

Graphite. — This  is  Ledebur's  "temper-carbon."    For  English-speaking  metallur- 

*  These  correspond  with  the  "  amorphous  iron  "  of  Dr.  Miiller. 


730  APPENDIX. 

gists  a  more  unfortunate  name  could  hardly  have  been  chosen.  "  Annealing  cat 
bon  "  would  have  been  better;  but  to  make  its  nature  quite  clear  the  author  wi 
throughout  this  paper  employ  the  name  graphite,  as  expressing  for  all  practice 
purposes  what  the  substance  is.  In  steel  it  occurs  in  the  form  of  dark  rounde' 
dots  (or  more  rarely  in  short,  worm-like  masses)  well  defined  against  a  backgroun< 
of  pale  iron. 

Sabcarbide  of  Iron  (or  0  iron). — But  one  more  constituent  remains  to  be  de 
scribed,  and  this,  if  Mr.  Osmond's  theory  be  true,  must  be  ft  iron  charged  with  dis 
solved  carbon.  On  lightly  etching  a  polished  section  consisting  mainly  of  thi 
compound  it  retains  its  polish  but  assumes  a  "black-leaded  "  appearance,  due  to  . 
very  faint  coating  of  dark  carbonaceous  matter.  It  seems  homogeneous  and  appar 
ently  non-crystalline,  but  probably  consists  of  minute  crystals,  the  junction-lines  o 
which  are  beyond  the  range  of  microscopic  vision  or  are  obscured  by  the  faint  car' 
bonaceous  deposit.  When  deeply  etched,  this  substance  becomes  covered  with  ; 
velvet  black  deposit,  which  may  be  removed  by  the  finger,  staining  the  latter.  Tin 
body  just  described  is  found  only  in  hardened  or  hardened-and-tempered  steel.  Th'i 
author  will  presently  produce  whats  eems  to  him  conclusive  microscopical  thermal 
and  magnetic  evidence  that  this  substance  is  not  an  allotropic  modification  of  iron 
but  a  definite  though  remarkably  attenuated  and  unstable  carbide  of  iron  of  intense 
hardness,  and  corresponding  with  the  formula  Fe24C. 

Details  of  Microscopic  Observations. 

The  structures  illustrated,  Plates  VII  and  VIII,  were  all  drawn  from  the  micro- 
scope, when  necessary  a  micrometer  being  used  on  correspondingly  graduated  circles 
28  inches  in  diameter.  The  drawings  were  then  reduced  by  photography  to  the 
diameter  of  the  microscopic  field.  The  labor  involved  in  carrying  out  this  process 
was  great,  but  the  results  depict  the  structures  with  an  accuracy  unattainable  bj 
direct  photography.  Direct  illumination  was  employed  throughout. 

Normal  Steel  No.  1,  PI.  VII  (Carben  0.08  per  cent). — The  structure  consists  oi 
irregular  crystals  of  iron,  amongst  which  are  sparingly  distributed  small  dark  knots 
of  the  diffused  normal  carbide  areas.  On  comparing  this  section  with  that  of  the? 
pure  iron,  it  will  be  seen  that  the  presence  of  even  0.08  per  cent  of  carbon  is  at 
once  decisively  revealed  by  the  microscope. 

Annealed  Steel  No.  1 1  (Carbon  0.08  per  cent).— The  effect  of  annealing  had  beenJi 
to  produce  a  distinct  increase  in  the  size  and  geometry  of  the  iron  crystals,  and  to* 
gather  the  Fe3C.  diffused  through  the  dark  normal  areas,  into  isolated  patches  of 
coarse  pearly  constituent  surrounded  by  thick  sectional  meshes  of  crystallized  Fe3C. 

Normal  and  Annealed  Steels,  No.  1|  (Carbon  0.21  per  cent). —These  sections 
were  in  all  respects  intermediate  between  those  of  steels  Nos.  1  and  2.  It  was  not 
therefore  deemed  necessary  to  illustrate  them. 

Normal  Steel,  No.  2,  PI.  VII  (Carbon  0.38  per  cent). — This  section  consists  of  a 
mixture  of  crystals  of  iron,  and  large  irregular  dark  areas  of  diffused  normal  carbide, 
the  latter  occupying  on  an  average  nearly  half  the  field. 

Annealed  Steel,  No.  2  PI.  VII  (Carbon  0.38  per  cent). — On  annealing,  the  iron! 
crystals  have  become  larger  and  more  definite,  whilst  the  dark  areas  have  aggregated; 
and  on  cooling  the  components  have  segregated,  forming  striaB  of  crystallized  Fe3C, 
divided  by  spaces  of  iron.  The  groups  of  striae  are  often  partly  surrounded  by  sec- 
tional meshes  of  Fe3C,  a  few  isolated  strias  of  which  compound  may  be  sometimes 
observed  between  the  junctions  of  the  iron  crystals. 

Annealed  Steel,  No.  2  t  (Carbon  0.38  per  cent). — This  section  gives  a  general 
view  of  the  structure  over  a  comparatively  large  area.  It  forms  a  beautiful  micro- 
scopic object  resembling  an  irregular  mosaic  pavement  composed  of  white  crystals 
of  iron  and  large  irregular  patches  of  the  pearly  constituent,  showing  splendid  inter- 
ference colors.  Of  course  a  magnification  of  100  times  a  linear  dimension  is  insuffi- 
cient to  resolve  the  striae  of  the  pearly  constituent. 

*  In  examining  the  engravings  of  the  sections  a  lens  will  be  found  useful  for  some  of  the  finer 
^structures 

t  This  figure  is  given  in  the  author's  plate,  but  was  not  reproduced  for  this  work.— J.  B.  J. 


F.LAT.B     V 11. 


0.38  C. 


oscopic  Sections  of  Steel,  magnified  500  diameters.     Treatment  and  per  cent  carbon  indicated. 
Drawn  by  Prof.  J.  O.  Arnold.     (Inst.  Civ.  Engrs.,  vol.  cxxiu.  (1896)  1 1.  4.) 


No.  4. 
Hardened. 


1.47  C. 


icroscopic  Sections  of  Steel,  magnified  500  diameters.     Treatment  and  per  cent  carbon  indicated 
Draws  by  Prof.  J.  O.  Arnold.     (Tnst.  Civ.  Engrs.,  vol.  cxxm.  (1896)  PI.  4.) 


STUDY  OF  IRON  AND  STEEL  BY  MICROQRAPHIC  ANALYSIS.    731 


TJie  General  Influence  of  Annealing  on  Mild  Cast  Steel. 

As  No.  2  steel  contains  about  the  same  percentage  of  carbon  as  that  contained  in 
high-class  castings,  it  will  be  well  to  discuss  in  connection  with  it  the  general  prin- 
ciples underlying  the  operation  of  flame  annealing.  The  surface  oxidation  of  carbon 
resulting  from  this  process  will  be  neglected,  as  its  effect  is  comparatively  small, 
and  only  the  action  of  annealing  on  the  main  portion  of  the  steel  which  is  unaltered 
in  ultimate  chemical  composition  will  be  considered. 

The  ideas  prevalent  among  metallurgists  on  this  subject  are  often  very  erroneous. 
It  has  been  stated,  both  in  text-books  and  in  practical  papers,  that  the  action  of 
annealing  is  to  produce  smaller  crystals.     As  a  matter  of  fact,  the  crystals  of  an 
annealed  steel  are  always  larger  than  those  existing  in  the  metal  before  annealing. 
The  idea  of  smaller  crystals  has  doubtless  arisen  from   a  confusion  of  effect  with. 
cause.     After  annealing,  the  crystals  of  the  fractured  metal  do  appear  to  the  eye 
smaller  than  those  in  the  original  material  ;  but  the  reason  for  this  is  found  in  the 
fact  that  during  the  process  of  rupture  they  elongate,  what  are  really  seen  being 
the  ends  of  the  ductile,  and  consequently  drawn  out,  crystals,  and  not  (as   in  the 
case  "of  the  comparatively  brittle  unannealed  metal)  the  originally  existing  facets. 
Also,  frequently,  what  are  regarded  as  crystals  in  the  fracture  of  a  brittle  unan- 
nealed steel  casting  are  really  groups  containing  many  crystals,  originally  bounded 
by  lines  of  great  intercrystalline  weakness,  along  which  rupture  has  naturally  taken 
place.     As  a  rule,  the  fracture  of  steel  bears  little  or  no  relation  to  its  triie^imcro- 
structure.     It  has  also  been  stated  that  on  annealing,  the  iron  and  the  pearly  constit- 
uent become  more  intimately  mixed  ;  for  which  Dr.  Sorby  has  been  quoted  as  the  au- 
thority.   Dr.  Sorby's  general  conclusion  on  this  matter  was  accurate,  and  was  exactly 
opposite   to   that  attributed  to  him.     The  mistake  seems   to  have  arisen  from  an 
imperfect  knowledge  of  the  meaning  of  the  word  "segregate."     The  true  action  of 
annealing  on  a  moderately  mild  steel,  containing,  say,  0.35  per  cent  of  carbon,  is  as 
follows:  1.  The  comparatively  small  and  distorted  crystals  of  the  original  metal 
become  larger  and  more  geometrical  in  form  (they  are  therefore  freer  from  internal 
stresses),  and  tiie  intercrystalline  cohesion,  if  originally  weak,  is  much  strength- 
ened.*    2.  The  carbonized  areas  existing  in  the  unannealed  steel,  chiefly  in  irregular 
elongated  masses,  gather  together  during  the  slow  cooling  into  rounded  or  harp- 
shaped  areas,  in  which  form  they  favor  the  continuity  of  the  iron  crystals  to  a  much 
greater  extent  than   the   original   arrangement.     3.  The   rounded  "or   harp-shaped 
areas,  into  which  are  concentrated  the  normal  carbide  of  iron  split  up  during  the 
slow  cooling  into  plates  of  crystallized  Fe3C,  separated  by  large  interspaces  of  iron; 
hence  the  latter  become  dovetailed  into  the  main  body  of  the  iron  crystals.     This 
continuity,  however,  is  not  perfect,  being  frequently  broken  by  the  sectional  meshes 
partly  environing  the  laminated  areas.     Thus  long  lines  formed  by  a  juxtaposition 
of  two  distinct  constituents  are  broken  up,  and  the  iron  becomes  almost  continuous 
throughout.     In  fact,  the  carbon  is  concentrated  into  small  plates  suspended  in  the 
iron,  mixed  with  only  about  5  per  cent  of  the  total  metal  instead  of  being  dis- 
tributed in  large  more  or  less  continuous  areas  forming  about  40  per  cent  of  the 
mass.     The  foregoing  statements  are  common  to  the  cases  of  forged  steel,  as  well  as 
of  the  metal  as  cast,  but  they  apply  with  peculiar  force  to  the  last-mentioned  mate- 
rial, in  which  the  intercrystalline  cohesion  is  usually  weak  ;  which  is  not  often  the 
case  in  forged  steels,  because  the  work  put  upon  the  material  has  already  repaired 
the  faulty  crystal-junctions  in  a  manner  analogous  to  the  influence  exercised  by 
annealing,  f 

In  order  to  render  the  above  facts  more  clear,  half-fields  of  No.  2  steel  in  the 
annealed  and  normal  conditions  are  exemplified  in  Fig.  14.  1  The  sections  from 
which  these  were  drawn  were  very  lightly  etched  so  as  to  bring  out  only  the  car- 
bonized constituents  without  developing  the  lines  marking  the  intercrystalline  junc- 

*  Perfect  intercrystalline  cohesion  is  synonymous  with  that  hitherto  mysterious  essence  known  to 
the  practical  man  as  "  body." 

t  The  question  of  the  influence  of  annealing  on  the  various  types  of  steel  castings  is  of  sufficient 
importance  to  warrant  its  special  consideration  in  a  separate  paper,  for  which  the  author  has  for 
some  time  past  been  collecting  data,  some  of  which  are  of  a  startling  nature.  ^^-""" 

i  Not  reproduced  here. 

**          * 


732  APPENDIX. 

\ 

tions.     The   several  sections  of  No.  2  steel  show  clearly  mat  existing  views  as  tc. 
steel  being  built  up  of  a  series  of  cemented  cells  are  erroneous.     As  already  stated, 
streaks  of  carbide  cement  may  now  and  then  be  seen  between  the  junctions  of  thtl 
iron  crystals,  but  such  constitute  incidents,  and  not  a  principle.     As  a  matter  olj 
fact,  if  "the  facets  of  the  iron  crystals  were  really  united  by  Fe3C  cement,  a  mile) 
steel   would   be  easily  fractured   by  a   blow  from   a    heavy   sledge-hammer.     The 
author,  from   the  results  of    many  experiments,  confidently  makes    the  following 
statement : 

If  the  cohesive  force  acting  between  the  facets  of  crystals  is  from  any  chemical, 
thermal,  or  mechanical  cause  seriously  weakened,  the  metal  will  appear  to  be  very 
brittle,  owing  to  rupture  under  the  influence  of  a  sudden  shock  occurring  along  the 
weak  junction-lines,  in  spite  of  the  fact  that  the  molecular  cohesion  may  be  perfect 
and  the  individual  crystals  ductile.* 

From  the  foregoing  statement  it  will  be  obvious  that  a  metal  may  be  soft  to  the 
drill  or  under  compression,  and  yet  brittle  under  impact,  exhibiting  little  or  no 
ductility  in  tension.  It  is  also  clear  that  in  such  a  case  chemical  analysis  is  useless. 
The  author,  however,  is  not  yet  prepared  to  state  the  exact  means  by  which  inter- 
crystalline  weakness  may  be  measured  by  the  microscope,  but  he  is  hopeful  that  in 
the  near  future  such  measurements  may  be  possible.  That  in  nearly  pure  iron  the 
intercrystalline  cohesion  and  the  molecular  cohesion  may  be  equal,  is  proved  by  the 
tensile  "test  of  No.  1  steel  annealed.  This  metal  is  composed  of  large  definite  crys- 
tals, yet  the  elongation  was  53  per  cent  and  the  reduction  of  area  at  the  point  of 
fracture  in  tension  was  77  per  cent. 

Normal  Steel  No.  3,  PI.  VII  (Carbon  0.59  per  cent). — In  this  section  the  dark  nor- 
mal carbide  areas  considerably  exceed  the  now  isolated  and  highly  distorted  crystals 
•of  iron. 

Annealed  Steel  No.  3,  PL  VII  (Carbon  0.59  per  cent).— This  section  confirms,  and 
presents  on  a  larger  scale  than  No.  2  steel  annealed,  the  breaking  up  of  the  dark 
areas  into  strise  of  crystallized  Fe3C  separated  by  interspaces  of  iron. 

Steel  No.  3|  (Carbon  0.74  per  cent).  Slightly  annealed.— This  section  was  in  all 
respects  intermediate  to  the  normal  sections  of  steels  Nos.  3  and  4,  containing  fewer 
iron  patches  than  the  former. 

Normal  Steel  No.  4,  PI.  VIII  (Carbon  0.89  per  cent).— This  section  presents  a 
feature  of  vital  importance  in  connection  with  the  theory  of  steel  which  the  author 
will  presently  enunciate.  The  entire  structure  consists  of  ill-defined  crystals  forming 
dark  areas  of  iron  containing  suspended  normal  carbide,  whilst  crystals  of  iron  free 
from  suspended  carbide  have  necessarily  altogether  disappeared.  In  other  words, 
iron  containing  0.89  per  cent  of  carbon  presents  a  critical  microscopical  point  which 
will  be  hereinafter  referred  to  as  the  "  saturation-point  ";  steels  in  which  the  carbon 
falls  below  0.89  per  cent  will  be  termed  "  unsaturated  " ;  whilst  steels  containing  more 
than  0.89  per  cent  carbon  will  be  distinguished  as  "  supersaturated,1'  for  reasons  to 
be  presently  stated. 

Annealed  Steel  No.  4,  PI.  VIII  (Carbon  0.89  per  cent).— This  section  consists  en-tirely 
of  crystals  of  the  pearly  constituent.  The  crystallized  striae  of  Fe3C  are  in  nearly 
parallel  lines,  some  straight,  others  wavy.  Small  isolated  masses  of  this  compound 
also  occur  sparingly.  The  thickness  of  the  plates  and  of  the  iron  interspaces  vary 
considerably.  In  one  area  the  hard  plates  are  in  such  relief  owing  to  the  wearing 
away  of  the  broad,  soft  iron  interspaces,  that  they  actually  cast  microscopic  shadows, 
as  indicated  in  the  figure.  The  microsection  of  this  steel,  consisting  entirely  of  the 
pearly  constituent,  presents  to  the  eye  a  beautiful  play  of  colors  resembling  those  of 
mother-of-pearl. 

Normal  Steel  No.  5,t  (Carbon  1.2  per  cent). — The  main  portion  of  this  section 
is  similar  to  that  of  normal  steel  No.  4,  but  each  crystal  or  group  of  crystals  is 

*  Purely  scientific  investigators  dealing  with  the  physics  of  iron  discourse  freely  on  molecules  and 
their  distances,  but  they  ignore  crystals  and  their  comparatively  huge  interspaces.  This  is  a  grave 
error;  e  g.,  there  is  little  doubt  that  magnetic  properties  are  much  influenced  by  the  dimensions  of  i 
the  crystals  into  which  the  molecules  are  grouped  The  author  emphatically  reiterates  that  deduc- 
tions explaining  observed  mechanical  facts  on  the  basis  of  allotropic  changes  in  the  molecular  archi 
tectures  of  metals  are  valueless,  unless  the  effects  due  to  crystalline  architecture  have  been  previously 
determined  and  allowed  for.  The  effects  due  to  the  first -mentioned  cause  are  often  very  small  in 
comparison  with  the  effects  produced  by  intercrystalline  causes. 

t  Not  reproduced  here. 


STUDY  OF  IRON  AND  STEEL  BY  MICROGRAPHIC  ANALYSIS.   733 

surrounded  by  a  sectional  mesh  of  Fe3C.  Isolated  striae  of  the  latter  compound  also 
occur.  It  must  be  remembered  that  the  strings  of  carbide  which  appear  sectionally 
as  a  coarse  and  irregular  network  are  in  reality,  when  translated  into  the  solid,  more 
or  less  perfect  investing  membranes.  This  statement  is  proved  by  the  fact  that  both 
transverse  and  longitudinal  sections  present  the  same  characteristics. 

Annealed  Steel  No.  5,*  (Combined  Carbon  0.92  per  cent,  Graphite  0.28  per 
cent). — This  section  possesses  features  of  special  interest.  It  presents  two  distinct 
types  of  field,  which  are  reproduced  in  two  half-fields.  In  one  will  be  observed  crys- 
tals or  groups  of  crystals  composed  of  the  pearly  constituent  enclosed  in  very  large 
sectional  meshes  of  Fe3C.  These  thick  membranes  have  evidently  resulted  from  a 
confluence,  during  the  slow  cooling,  of  the  comparatively  small  membranes  present 
in  the  normal  steel.  In  parts  of  the  section  from  which  meshes  are  absent  there  are, 
however,  round  almost  black  patches  of  graphite,  set  for  the  most  part  in  the  centres 
of  round  patches  of  bright  iron,  the  remainder  of  such  field  being  as  usual  composed 
of  the  pearly  constituent.  It  would  therefore  appear  that  when  the  mobilized  masses 
of  carbide  attain  a  certain  magnitude,  they  act  during  the  slow  cooling  like  very 
highly  carbonized  white  pig-iron,  ^dissociating  into  nearly  pure  iron  and  graphite. 
The  temperature  at  which  this  separation  takes  place  will  be  considered  in  connec- 
tion with  the  annealed  sample  of  No.  6  steel. 

Normal  Steel  No.  6,  PL  VIII  (Carbon  1.47  per  cent). — In  this  section  the  dark 
background  of  iron  permeated  with  diffused  Fe3C  is  much  broken  up  by  thick  irreg- 
ular meshes  of  crystallized  Fe3C.  The  enclosed  crystals  also  contain  large  fern-like 
streaks  of  the  crystallized  carbide,  the  whole  constituting  a  beautiful  and  striking 
microscopic  object. 

Annealed  Steel  No.  6,  PI.  VIII  (Combined  Carbon  0.33  per  cent,  Graphite  i.!4  per 
cent). — In  this  section  about  one  third  of  the  area  consists  of  the  pearly  constituent, 
the  other  two  thirds  being  composed  of  iron  crystals  largely  spotted  with  dark  round 
patches,  and  short  worm-like  masses  of  graphite.  The  latter  must  have  separated 
below  the  temperature  of  the  carbon  change  point  AR  1,  which  is  about  685°  C.,  be- 
cause the  large  masses  of  carbide  described  in  connection  with  annealed  steel  No.  5 
would  in  the  present  case  be  still  greater;  and  not  only  have  they  become  totally  de- 
composed, but  have  evidently  also  gathered  in  much  of  the  carbide  existing  as  small 
plates  in  the  pearly  constituent.  Hence,  as  the  plates  so  collected  would  not  have 
crystallized  till  the  temperature  had  fallen  to  about  680°  C.,  it  appears  certain  that 
the  decomposition  of  the  Fc3C  into  iron  and  graphite  must  take  place  at  or  below 
AR  1  i.e.,  at  a  low  red  heat.  The  interesting  fact  that  this  dissociation  is  facilitated 
by  pressure  is  proved  by  the  investigations  of  Mr.  B.  W.  Winder,  who  found  that 
hard  file-steel  leaving  the  rolls  at  a  low  red  heat  almost  invariably  contained  graph- 
ite in  large  quantities,  whilst  similar  steel  finished  at  a  fair  red  heat  was  almost  de- 
void of  free  carbon. 

Annealed  Steel  No.  6,*  (Combined  Carbon  0.33  percent,  Graphite  1.14  per  cent). — 
This  section  presents  a  large  area  of  the  graphitic  metal,  showing  the  crystals  of 
iron,  the  spots  of  graphite,  and  the  curiously  irregular  masses  of  the  pearly  con- 
stituent in  which  is  contained  the  0.33  per  cent  of  combined  carbon  present.  At  100 
diameters  the  microscope  is  of  course  incapable  of  resolving  the  striae  of  the  pearly 
constituent,  which,  however,  presents  a  play  of  gorgeous  colors.  From  the  three 
graphitic  sections  referred  to,  it  will  be  seen  that  supersaturated  steels  are  always 
very  liable  to  deposit  graphite  on  annealing.  Such  a  phenomenon  is  seldom  or  never 
observed  on  or  below  the  saturation-point. 

The  foregoing  microscopical  facts  have  been  known  to  the  author  for  about  three 
years,  having  been  ascertained  by  an  examination  of  another  series  of  steels  similar 
to  those  now  under  consideration.  But  as  it  was  unexpectedly  found  that  the  harder 
steels  contained  about  0.3  per  cent  of  manganese,  the  author  rejected  the  first  series, 
and  made  a  purer  set  of  steels  upon  which  to  commence  the  research  afresh.  As  the 
result  proved,  the  comparatively  high  manganese  in  the  hard  steels  did  not  seriously 
affect  the  results  just  described,  and  the  first  series  now  constitute  confirmatory 
evidence,  which  has  also  been  augmented  by  the  examination  of  many  samples  of 
commercial  steels. 

*  Not  reproduced. 


734  APPENDIX. 


General  Theory  Based  on  the  Microscopical  Results. 

The  evidence  given  by  the  microstructure  of  the  steels  is  thus  interpreted  by  the 
author: 

1.  The  sharply  defined  localization  of  the  areas  containing  respectively  the  dif- 
fused normal  and  crystallized  carbides  (until  the  saturation-point  at  0.89  per  cent  of 
carbon  is  reached)  seems  to  confirm  beyond  doubt  the  accuracy  of  the  general  con- 
clusion of  Dr.  Sorby — that  at  high  temperatures  a  compound  of  iron  and  carbon 
exists,  which  on  cooling  splits  into  iron  and  an  intensely  hard  compound  very  rich 
in  carbon. 

2.  The  fact  that  the  dark  carbonized  areas  of  normal  steels  increase  proportion- 
ally to  the   carbon  until  the  saturation-point  is  reached  seems  quite  incompatible 
with  the  theory  that  at  a  high  temperature  the  carbon  is  in  a  free  state  in   mere 
solution.     Under  such  conditions  the  carbide  of  iron  would  be  evenly  diffused  after 
its  deposition  in  situ  on  cooling,  and  would  on  etching  yield  an  almost  homogeneous 
microscopic  field,  darkening   in  color   as  the  carbon  increased  ;  inasmuch   as  the 
stronger  the  solution  at  high  temperatures,  the  greater  the  amount  of  diffused  carbide 
in  the  cold  metal,  and,  cceteris  paribus,  the  thicker  the  deposit  of  carbonaceous  col- 
oring matter  released  on  the  surface  of  the  etched  section. 

If  it  be  admitted  that  the  dark  areas  in  normal  steels  and  the  striated  areas  in 
the  corresponding  annealed  metals  are  mixtures  resulting  from  the  decomposition  of 
a  compound  existing  at  temperatures  above  the  change-point  AR  1,  it  necessarily  fol- 
lows that  at  the  saturation-point  (at  0.89  per  cent  of  carbon)  the  whole  mass  of  the 
iron  is  at  a  full  red  heat  in  combination  with  the  carbon,  and  hence  that  the  percent- 
age of  carbon  in  the  saturated  steel  is  also  the  percentage  of  carbon  in  the  formula 
of  the  compound.  Therefore  the  compound  will  contain  0.89  per  cent  of  carbon 
and  99.11  per  cent  of  iron,  corresponding  with  the  formula  Fe24C,  which  requires 
0.884  per  cent  of  carbon. 

In  the  case  of  a  supersaturated  steel  made  by  gradually  adding,  say  1.5,  per  cent 
of  carbon  to  pure  iron  in  a  molten  state :  when  the  iron  has  combined  with  0.89  per 
cent  of  carbon  it  will  have  been  converted  into  a  carbide  of  formula  Fe24C  ;  but  on 
adding  more  carbon  a  portion  of  the  subcarbide  will  be  carbonized  to  the  normal 
carbide  Fe3C  ;  thus- 

Fe24C  4-  7C  =  8Fe3C. 

The  molten  mass  then  consists  of  a  mixture  of  the  normal  carbide  with  subcar- 
bide of  iron.  On  cooling,  the  subcarbide  decomposes  into  ill-defined  crystals  of 
iron  permeated  with  diffused  Fe3C,  whilst  the  surplus  normal  carbide  is  thrown  off 
in  the  form  of  membranes  enveloping  the  irregular  crystals  of  the  mixture  resulting 
from  the  decomposition  of  the  subcarbide. 

The  Structure  of  Hardened  Steels. 

To  obtain  more  conclusive  microscopic  evidence  of  the  accuracy  of  the  theory  just 
enunciated,  it  was  obviously  necessary  to  determine  the  structure  of  hardened  steel 
below,  on,  and  above  the  saturation-point.  When  it  is  remembered  that  even  the 
skill  of  Dr.  Sorby  was  baffled  in  all  his  efforts  to  obtain  satisfactory  sections  of  hard- 
ened steel,  it  is  not  surprising  that,  although  possessing  superior  appliances,  the 
author's  experiments  in  this  direction  were  for  several  years  almost  fruitless,  yield- 
ing most  puzzling  and  erratic  results.  However,  comparatively  recently,  the  author 
possessed  himself  of  the  key  to  the  position,  in  the  fact  that  it  was  absolutely  neces- 
sary to  harden  the  samples  from  a  nearly  white  heat,  without  allowing  them  to  come 
into  contact  with  either  air  or  water.  This  was  because  the  decarbonizing  action  of 
a  film  of  magnetic  oxide  on  the  surface  of  a  piece  at  a  full  red  heat  extended  irregu- 
larly to  such  a  depth  that  it  was  almost  impossible  in  the  flint  hard  steels  to  grind 
off  the  partially  decarbonized  surfaces  without  disturbing  the  structure  or  "letting 
down  "  the  steel.  This  fatal  defect  was  finally  removed  by  the  following  simple 
though  somewhat  costly  plan.  Each  microsection  was  polished  and  encased  air-tight 
in  thin  plates  of  the  same  steel  in  the  manner  indicated  in  Fig.  637.  The  encased 


STUDY  OF  IRON  AND  STEEL  BY  MICROORAPHIG  ANALYSIS.   735 

microsection  was  then  slowly  heated  to  about  1050°  C.,  and  was  quenched  with  the 
greatest  possible  rapidity  in  a  large  tank  of  ice-cold  water.  On  drying  and  removing 
the  casings  the  section,  although  it  had  been  heated  during  half  an  hour  up  to  an 


FIG.  637.— Twice  full  size. 

incipient  white  heat,  was  found  to  be  quite  bright  and  absolutely  unoxidized  on  the 
lower  polished  face.  On  lightly  etching  three  typical  sections  the  following  results 
were  obtained: 

Hardened  Steel,  No.  2,  PI.  VII  (Carbon  0.38  per  cent).— On  being  etched,  the 
sample  assumed  a  roughish  texture  and  a  dull,  somewhat  dark-gray  tint.  On 
lightly  removing  the  gray  deposit  the  steel  was  found  to  consist  of  two  distinct  con- 
stituents, viz.,  free  iron  and  an  amorphous  substance  to  which  the  acid  had  commu- 
nicated a  dark  color.  In  some  fields  the  iron,  and  in  others  the  dark  constituent, 
predominated.  The  author  affirms  the  latter  to  be  subcarbide  of  iron.  The  section 
figured  represents  an  average  field.  The  shock  of  the  sudden  cooling  seems  to  have 
dispersed  the  iron  through  the  dark  substance  in  masses  irregular  in  size  and  fan- 
tastic in  shape — many  particles,  no  doubt,  being  too  small  for  separate  microscopic 
definition. 

Hardened  Steel,  No.  4,  PI.  VIII  (Carbon  0.89  per  cent).— This  section,  on  being 
very  lightly  etched,  retained  its  polish,  but  assumed  a  "  blackleaded"  appearance. 
When  examined  under  the  microscope  the  field  at  first  sight  presented  a  brownish- 
colored  blank,  in  which  no  crystalline  structure  could  be  detected.  •  A  prolonged 
and  careful  examination  showed  that  the  section  really  possessed  an  indefinite* 
granular  roughness,  but  no  crystalline  junctions  could  be  detected.  It  is,  however, 
probable  that  the  mass  really  consists  of  minute  crystals,  the  boundary-lines  of 
which  are  beyond  the  reach  of  microscopic  vision  or  are  rendered  indefinable  by  the1 
faint  carbonaceous  deposit.  This  is  the  only  practically  homogeneous  section  the 
author  has  ever  obtained  during  many  years  of  close  study  of  the  microstructure 
of  steel  and  iron. 

Hardened  Steel,  No.  6,  PI.  VIII  (Carbon  1.47  per  cent).— On  being  etched,  this 
section  behaved  in  every  respect  like  hardened  steel  No.  4.  The  groundwork  of  the 
section  was  also  found  to  be  identical  with  the  saturated  metal,  but  all  over  it  was 
spread  a  network  of  fine  meshes,  together  with  isolated  stria3  and  irregular  dots  of 
a  substance  microscopically  corresponding  in  all  respects  to  Fe3C. 

Thus  the  microstructures  of  the  hardened  steels  seem  in  accordance  with  the 
author's  theory.  The  unsaturated  steel  possesses  a  structure  such  as  might  be  ex- 
pected from  a  suddenly  quenched  mixture  of  free  iron  and  subcarbide  of  iron.* 
The  saturated  steel  fulfils  the  necessary  theoretical  condition  of  homogeneity,  whilst 


*  The  non-homogeneous  nature  of  hardened  unsaturated  steel  is  best  seen  in  oil-quenched  gun- 
steel  containing  about  0.3  per  cent  of  carbon,  the  almost  black  subcarbide  areas  being  fantastically 
enmeshed  in  free  iron. 


736  APPENDIX. 

the  supersaturated  steel  decidedly  reveals  the  presence  of  surplus  meshes  of  normal 
carbide  of  iron. 

NOTE  BY  THE  AUTHOR. 

Photomicrographs  of  Steel— The  microscopic  sections  shown  in  Plates  VII  and 
VIII  are  from  drawings.  Those  shown  in  Plates  IX,  X,  and  XI  are  reproduced 
photographs,  taken  directly  from  the  specimen,  and  they  reveal  these  just  as  they 
would  appear  to  the  observer,  so  far  as  can  be  done  by  photography.  The  drawings 
indicate  the  crystalline  arrangement  much  better  than  the  photographs,  but  reliance 
must  be  placed  in  the  competency  and  faithfulness  of  the  draughtsman,  who  is  of 
course  the  observer.  With  the  photographs  the  personal  equation  of  the  observer 
is  eliminated.  The  two  taken  together  reveal,  to  some  extent,  the  merits  and  the 
possibilities  of  this  method  of  analysis.  Each  of  these '  methods  of  illustration  has 
its  advocates,  the  chief  of  whom  to-day  are  perhaps  the  respective  authorities 
here  quoted— Arnold  and  Martens. 


PLATE    IX. 


Bessemer    Steel    Ingot,    showing   blow-hole. 
Magnified  .35  diameters. 


m 

.tfofcL."  SwMtiifKri 


Open-hearth     Steel     Ingot.      Magnified    10 
diameters. 


Rolled    Open-hearth     Steel.       Magnified     36 
diameters. 


eters. 


Mild  Steel  after  breaking  in  tension.    Mag- 
nified 14  diameters. 


Mild  Steel   showing   defects.     Magnified   14 
diameters. 


PHOTOMICROGRAPHS  OF  STEEL.     (After  Martens.) 


PLATE   X 


Thomas  Steel  Ingot. 
Magnified  60  diameters 


Rolled  Manganese  Steel,  10.6$  Mn. 
Magnified  30  diameters. 


Open-hearth  Steel  Ingot. 
Magnified  400  diameters 


Rolled  Manganese  Steel,  10.6£  Mn. 
Magnified  8  diameters. 


Open-hearth   Steel  Ingot. 
Magnified  85  diameters. 


~* 


•  •*• K'  5f  ,:•  k»T  V\K.  J 


Cast  Steel. 
Magnified  a5  diameters. 


PHOTOMICROGRAPHS  OF  STEEL.     (After  Martens. 


PLATE   XL 


From  a  Steel-rail  Web. 
Magnified  10  diameters. 


From  a  Steel-rail  Head. 
Magnified  10  diameters. 


From  a  Steel-rail  Head. 
Magnified  70  diameters. 


From  a  Steel-rail  Web. 
Magnified  2iH)  diameters. 


From    a    Broken  Test-specimen, 
showing  Defects.     Mag.  14  diam. 


From  a  Steel-rail  Web. 
Magnified   10  diameters. 


From  a  Steel-rail  Head. 
Magnified  200  diameters. 


From  a  Steel-rail  Head. 
Magnified  1(K)0  diameters. 


PnoTOMicnooKAPHS  OF  STEEL     (After  Martens.) 


APPENDIX  C. 

COMPARATIVE  ANALYSIS  OF  THE  RESOLUTIONS  OF  THE  CONVENTIONS 
OF  MUNICH,  DRESDEN,  BERLIN,  AND  VIENNA,  AND  THE  RECOM- 
MENDATIONS OF  THE  AMERICAN  SOCIETY  OF  MECHANICAL  ENGI- 
NEERS, WITH  THE  CONCLUSIONS  ADOPTED  BY  THE  FRENCH  COM- 
MISSION IN  REFERENCE  TO  THE  TESTING  OF  METALS. 

By  Mr.  L.  BACLE, 

Member  of  the  French  Commission  on  Methods  of  Testing  the  Materials  of  Construction. 

Translated  by  O.  M.  CARTER,  Capt,  Corps  of  Engrs.  U.  S.  A.,  and 
E.  A.  CIESELER,   U.  S.  Asst.  Eugr. 

INTRODUCTION. 

Two  attempts  have  been  made  abroad  to  secure  the  adoption  of  uniform  methods 
of  testing  construction  materials — one  under  the  auspices  of  technical  conventions 
held  at  different  times  in  Munich,  Dresden,  Berlin,  and  Vienna,  where,  besides  the 
German  members,  there  were  present  delegates  representing  various  foreign  coun- 
tries; the  other,  in  America,  under  the  auspices  of  the  American  Society  of  Mechan- 
ical Engineers.  Two  reports  presented  to  the  Committee  of  Research,  one  by  M. 
Polonceau  and  the  other  by  M.  Bade,  have  given  translations  of  the  conclusions  and 
recommendations  thus  adopted  by  the  Conventions  and  by  the  American  Society. 

It  is  proper,  therefore,  to  make  a  comparison  between  the  resolutions  adopted  by 
foreign  conventions  and  those  adopted  by  our  own  commission,  in  order  that  we  may 
examine  the  differences  and  analogies  which  they  present.  Such  a  comparison  affords 
an  opportunity  of  deciding  whether  there  should  be  renewed  study  and  research  upon 
the  points  of  difference,  and  of  determining  whether  we  may  hope  for  international 
unity  in  the  future,  based  upon  the  common  resolutions  already  recommended  and 
even  now  adopted  in  the  current  practical  domestic  relations  of  different  countries. 

The  work  of  comparison  in  the  present  report,  intended  in  some  measure  to  form 
a  starting-point  for  the  studies  of  an  international  commission  which  might  be  crea- 
ted for  this  purpose,  has  been  confined  to  the  methods  of  testing  metals,  which  is 
the  sole  subject  of  discussion  in  Section  A.  (Section  des  Metaux.) 

To  facilitate  comparison,  avoiding  as  much  as  possible  all  omissions,  an  attempt 
has  been  made  to  place  together  all  resolutions  relating  to  the  same  subject,  and  to 
this  end  the  methods  of  classification  used  in  our  General  Report  have  been  adopted. 
The  present  report  follows,  therefore,  the  divisions  and  rules  of  the  General  Report, 
giving  under  each  chapter  only  such  resolutions  as  offer  a  possibility  of  comparison 
with  the  corresponding  foreign  recommendations. 

The  comparison  is  usually  made  by  referring  to  the  resolutions  of  the  Conventions, 
for  those  are  frequently  reproduced  in  the  recommendations  of  the  American  Society. 
In  certain  cases,  however,  those  two  groups  of  resolutions  present  differences  which 
then  become  the  subject  of  special  mention. 

It  is  advisable  to  point  out  in  a  general  way,  among  the  resolutions  to  be  com- 
pared, a  primary  difference  in  principle  (which  is,  however,  of  little  importance)  re- 

737 


738  APPENDIX. 

lating  to  tests  made  upon  finished  pieces.  The  resolutions  of  the  Conventions,  iden- 
tical in  this  respect  with  the  resolutions  of  the  American  Society,  define  the  tests 
which  should  be  made  upon  certain  articles  in  current  use,  such  as  tires,  axles,  and  ' 
rails.  For  certain  kinds  of  metals,  such  as  wrought  or  cast  iron,  for  different  speci- 
fied uses,  they  advise  the  discarding  of  such  tests  as  to  them  seem  unnecessary,  while 
our  Commission  refuses  to  make  any  such  elimination,  feeling  totally  unauthorized 
to  do  so. 

With  regard  especially  to  methods  of  testing,  the  studies  of  our  Commission  have 
been  more  general  than  those  made  abroad,  and  the  recommendations  that  we  have 
made  include  various  kinds  of  tests  not  mentioned  in  the  foreign  resolutions,  with 
which,  therefore,  no  comparison  is  possible. 

On  the  other  hand,  certain  methods  of  testing  have  been  especially  recommended 
in  all  of  the  resolutions,  such  as  tensile,  shock,  and  bending  tests,  and  it  is  with  re- 
spect to  those  that  the  committee  should  make  special  comparative  examinations. 

In  tensile  tests  the  Conventions  do  not  define  so  definitely  as  do  we  the  quantities 
to  be  measured;  they  do  not  give  the  same  limits  of  approximation  in  their  meas- 
ures; they  follow  the  law  of  similarity  in  adopting  cylindrical  test-pieces,  but  use  a 
different  coefficient  from  ours,  which  tends  to  give  to  the  useful  or  test  length  a 
greater  value  for  the  same  diameter.  Other  differences  are  apparent  in  the  descrip- 
tion of  their  standard  rectangular  test-pieces. 

The  American  Society  prescribes  an  invariable  standard  of  test  length,  indepen- 
dent of  both  the  diameter  and  the  cross-section  of  the  test-piece. 

The  resolutions  of  the  Conventions  concerning  shock  tests  are  confined  almost 
entirely  to  finished  pieces.  They  give  more  explicit  directions  than  do  we  in  regard 
to  the  arrangement  ol  the  apparatus  employed,  but  certain  experiments  made  upon 
test-pieces  that  we  have  especially  studied  are  not  mentioned  by  them. 

In  bending  tests  they  recommend  that  the  bending  should  be  done  around  a 
mandrel  of  unvarying  diameter,  while  the  American  Society  claims  that  the  mandrel 
should  vary  in  proportion  to  the  thickness  of  the  test-piece.  The  dimensions  of 
their  bars  differ  also  from  those  used  by  us. 

The  differences  just  given  are  the  most  marked  ;  but  they  are  in  reality  of  little 
importance,  and  probably  can  be  easily  overcome. 

In  the  general  resolutions  concerning  the  precautions  to  be  observed  in  preparing 
test-pieces  we  find  at  times  differences  of  detail,  but  they  are  usually  of  minor 
importance,  since  the  three  sets  of  resolutions  upon  that  subject  are  inspired  by  the 
same  general  principles. 

In  so  far  as  the  general  formulas,  as  well  as  the  methods  of  testing  referred  to 
above,  are  concerned,  we  find  as  a  result  of  this  comparison  nothing  to  indicate  that 
the  desired  unity  of  method  may  not  be  attained  should  an  international  commission, 
be  called  for  that  purpose. 

FIBST  AND  SECOND  PAKTS. 
PHYSICAL  EXAMINATION  AND  CHEMICAL  TESTS. 

The  resolutions  of  the  Conventions  do  not  contain  any  specific  directions  upon 
those  subjects,  but  they  advise  the  acquisition  of  as  thorough  a  knowledge  as  possi- 
ble of  the  results  of  both  microscopic  and  chemical  examinations,  especially  in  all 
cases  of  scientific  research. 

According  to  the  recommendations  of  the  American  Society,  the  magnetic  condi- 
tion of  a  metal  should  be  especially  mentioned. 

Those  recommendations  require,  moreover,  that  when  in  tensile  tests  the  rup- 
tured section  presents  a  cupel  form  the  fact  should  be  mentioned,  the  relative  posi- 
tion of  the  edges  of  the  cupels  with  reference  to  each  of  the  pieces  of  the  tested  bar 
being  indicated. 

To  determine  the  effects  of  tempering  upon  steel,  the  American  Society  recom- 
mends in  addition  that  the  bars  should  be  heated  to  a  bright  red  and  immediately 
quenched  in  water  at  from  32°  to  40°  F.  (0°  to  5°  C.) 

Our  Commission  requires  that  the  test-bars  should  be  heated  to  a  comparatively 
deep  cherry-red  and  quenched  in  water  at  28°  C.,  the  volume  of  water  being  great 
in  proportion  to  the  volume  of  the  bars. 


UNIFORM  METHODS  OF  TESTING  METALS.  739 

The  resolutions  of  the  Conventions  also  require  that  the  metal  should  be  heated 
to  a  cherry-red  (placed  by  them  at  from  550°  to  600°  C.)  and  quenched  in  water  at 
25°  C. 

They  recommend  also,  as  will  be  seen  later  on,  that  copper  test-pieces  should  be 
heated  to  700°  C.  and  quenched  in  water  at  15°  C. 

That  recommendation  is  not  found  among  our  conclusions,  which  require,  how- 
ever, that  deductions  from  experiments  with  copper  or  its  alloys  shall  be  drawn 
from  tests  made  after  the  last  annealing  in  the  manufacture  of  the  plates. 

THIRD  PART. 
MECHANICAL  TESTS.— RECOMMENDATIONS  COMMON  TO  ALL  METHODS    OF  TESTING. 

CHAPTER  I.*— GENERAL  OBSERVATIONS.     • 

Our  resolutions  show  the  importance  of  accompanying  mechanical  tests  of  what- 
ever nature  with  the  tensile  test ;  they  indicate  the  approximate  exactitude  with 
which  one  should  be  content  in  the  majority  of  current  tests,  by  showing  that  in 
practical  experiments  the  exaggerated  precision  required  in  scientific  research  is  not 
necessary.  They  avoid,  moreover,  giving  any  indication  regarding  a  choice  between 
the  various  methods  of  testing  according  to  the  application  proposed. 

The  resolutions  of  the  Conventions  recommend  generally  that  testing  should  be 
done  with  reference  to  the  work  to  which  the  pieces  are  to  be  subjected  ;  at  the 
same  time  they  indicate  which  test  to  adopt  and  which  to  reject  in  specified  cases  ; 
they  advise  the  adoption  of  regular  tests  for  certain  pieces  frequently  employed, 
such  as  rails,  tires,  and  axles  for  railroad  use,  cast  or  wrought  iron,  materials  for 
shipbuilding,  etc.,  recommending  the  greatest  possible  number  of  tests  upon  all 
pieces  of  the  same  delivery,  testing  without  damaging  them. 

They  recommend,  for  instance,  testing  tires  and  axles  by  shock  with  a  standard 
impact  machine,  claiming  that  it  is  useless  to  test  tires  by  a  hand-hammer  or  axles 
by  flexure.  They  add  that  it  may  be  advisable  to  have  recourse  to  tensile  tests  to 
obtain  certain  additional  complemental  information. 

They  confine  themselves  to  recommending  that  the  degree  of  exactitude  attained 
in  the  tests  should  be  stated,  or  at  least  that  data  should  be  furnished  allowing  it  to 
be  determined. 

The  resolutions  of  the  American  Society  recommend  that  tests  should  be  made  as 
far  as  possible  upon  the  pieces  themselves  whose  quality  it  is  desired  to  ascertain, 
being  careful  to  reproduce  as  far  as  possible  the  conditions  to  which  the  pieces  will 
be  subjected  when  in  use.  They  add,  with  a  view  to  facilitate  comparison,  that  it 
would  be  well  to  make  a  standard  test  over  and  above  the  tests  upon  finished  pieces. 

With  regard  to  registering  apparatus,  our  Commission  limits  itself  to  saying 
that  it  should  be  employed  without  hesitation,  as  its  use  even  when^  it  is  not  posi- 
tively accurate  may  prevent  serious  error. 

The  American  Society  seems,  however,  to  recommend  it  more  formally,  especially 
for  tensile  tests. 

In  regard  to  test-pieces  that  are  imperfect,  our  resolutions  require  that  they 
shall  be  thrown  out  of  the  calculation  of  averages  established  from  a  scientific  point 
•of  view  whenever  there  are  exceptional  or  local  defects  in  the  test-pieces. 

The  American  Society  remarks  on  this  subject  that  in  making  tests  all  pieces  of 
abnormal  appearance  or  those  showing  superficial  defects  should  be  rejected.  If,  how- 
•ever,  a  perfect  piece  cannot  be  found,  a  record  of  the  imperfections  should  be  kept. 

CHAPTER  IL— PREPARATION  OF  TEST-PIECES. 

CONDITION  OF  THE  METAL. 

Our  resolutions  recommend  in  general  that  the  condition  of  the  metal  employed 
shall  be  precisely  defined  principally  with  respect  to  hammer-hardening  (ecrouissage)^ 


*  The  "  chapters  "  here  referred  to  are  the  chapters  of  Part  Three  (Vol.  I)  containing  the  recom- 
mendations of  the  French  Commission  in  reference  to  the  Testing  of  Metals. 

t  Hammer  or  cold  hardening  (ecrouissage)  is  an  alteration  produced  by  working  a  metal  when  cold 
"With  a  hammer,  a  die,  a  punch,  shears,  etc.  Ecrouissage  is  the  standard  change  in  a  metal  which  has 
[been  subjected  to  a  permanent  deformation  at  a  temperature  lower  than  that  required  for  annealing. 


740  APPENDIX. 

and  especially  when  soft  metals  are  used,  that  the  test-pieces  shall  not  be  removed 
until  the  metal  has  been  brought  to  the  exact  condition  under  which  it  is  decided  to 
test  it ;  they  mention  also  the  precautions  to  be  taken  in  finishing  off  test-pieces,  in 
order  to  avoid  any  strain  which  might  produce  a  change  in  the  condition  of  the 
metal. 

The  American  Society  also  insists  upon  the  importance  of  observing  its  resolutions, 
which  state  that  the  lightest  blow  from  a  hammer,  or  any  blow  incorrectly  given, 
may  falsify  results,  should  the  abnormal  strain  thus  produced  be  greater  than  that 
required  to  cause  variation  in  the  quality  of  the  metal  to  be  tested. 

They  admit,  moreover,  that  soft  metals  are  less  susceptible  to  those  influences 
than  hard  metals. 

With  regard  to  plates  of  mild  steel,  the  Conventions  have  decided  that  it  is 
unnecessary  to  test  them  after  they  have  been  annealed,  as  it  is  too  difficult  to  deter- 
mine the  exact  temperature  of  annealing.  They  add,  in  conclusion,  and  in  accord 
with  our  Commission,  that  the  object  generally  sought  is  to  ascertain  the  nature  of 
the  metal  in  the  condition  when  delivered. 

THE    PLACE    AT    WHICH    AND    THE    MANNER    IN   WTHICH    TEST-PIECES    SHOULD    BE    CUT. 

FABRICATION   OF  TEST- BARS. 

The  resolutions  of  the  Conventions  require,  for  instance,  with  rails,  that  the  bars 
detached  shall  have  square*  sections  and  contain  the  exterior  fibres  of  the  rail.  Our 
advice  is  in  general  to  take  the  test-bars  from  the  thinnest  and  thickest  parts  of  the 
final  rolled  section. 

With  regard  to  plates,  the  resolutions  of  the  Conventions  are  imbued  with  the 
same  spirit  as  ours,  from  which  they  vary  only  in  minor  details.  They  advise  taking 
the  test-pieces  from  the  longitudinal  and  transverse  sides,  cutting  away,  when  raw 
or  uncut  plates  are  used,  at  least  30  millimeters  in  width  from  the  exterior  ;  when 
dressed  plates  are  used  the  test-pieces  should  be  chosen  from  plane  plates  of  regular 
thickness. 

They  admit,  without  going  further  into  details,  that  the  strips  should  be  cut  with 
shears  or  by  a  saw,  but  for  bridge  iron  or  boiler-plates  they  require  that  the  strips 
cut  off  by  shears  shall  be  straightened  out  cold  by  a  press,  by  the  use  of  a  wooden 
mallet,  or  by  small  hammers  of  lead  or  copper.  Before  cutting  out  the  test-pieces 
the  strips  should  be  planed  down  on  each  side  for  a  width  of  at  least  5  millimeters 
to  do  away  with  the  effect  of  the  shears.  Upon  express  demand  annealing  is  per- 
mitted for  straightening  out  strips  cut  by  shears  from  boiler-plates. 

Our  resolutions  impose  more  minute  precautions  to  prevent  the  deformation  of 
the  bars,  and  if  annealing  is  indispensable  for  straightening,  they  require  that  a 
temperature  of  700°  C.  shall  not  be  exceeded. 

They  require  also  that  the  test-pieces  shall  be  cut  from  the  strips  by  a  machine, 
without,  however,  stipulating  that  a  depth  of  5  millimeters  in  thickness  of  the  metal 
shall  be  removed. 

For  rolled  products,  the  resolutions  of  the  Conventions  prescribe  that  the  rough- 
rolled  surfaces  shall  be  preserved.  Our  instructions  do  not  mention  that  point,  but 
it  may  be  observed  that  in  practice  that  method  is  always  followed. 

The  Conventions  require,  finally,  that  the  reports  of  tests  shall  make  known  the 
source  and  the  method  of  manufacture  of  the  test-pieces,  and  they  add  that  those 
pieces  designed  for  compression  tests  should,  as  far  as  possible,  be  smoothed  by 
planing  or  turning. 

In  the  preparation  of  test-pieces  of  copper,  they  recommend  the  most  minute 
precautions,  which  are  also  mentioned  in  our  resolutions. 

Besides  those,  they  add,  as  has  been  indicated  above,  that  bars  of  copper  should 
be  annealed  at  700°  C.t  before  they  are  completed,  then  cooled  in  the  air  to  a  dull 
red,  and  finally  quenched  in  water  at  15°  C.,  while  our  resolutions  demand  that  tests 
shall  be  made  after  the  last  annealing  in  the  fabrication  of  the  plates. 

In  regard  to  test-pieces  of  cast  iron,  the  Conventions  require  that  they  shall  be 
cast  in  a  mould  of  very  dry  sand  having  an  inclination  of  10  centimeters  per  meter. 

*  The  original  resolutions  require  only  a  rectangular  section.  — O.  M.  C. 

t  That  temperature  must  not  be  exceeded.     See  Original  Resolutions.— O.  M.  C. 


UNIFORM  METHODS  OF  TESTING  METALS.  741 

The  entrance  for  the  flow  of  the  melted  material  should  be  placed  20  centimeters 
above  the  mould,  determining  thus  the  length  of  the  runner-stick.  Those  test-pieces 
should  be  left  with  the  rough  surfaces  produced  by  the  moulds. 

Our  resolutions  require  that  for  pieces  which  at  some  places  are  more  than  9 
centimeters  thick  the  test-bars  should  be  cut  by  a  machine  from  the  foot  of  the 
runner-stick.  For  other  pieces  the  test-bars  may  be  cast  separately,  if  care  be  taken 
to  give  the  mould  an  inclination  of  about  20  centimeters  per  meter  and  to  make  the 
runner-stick  from  15  to  20  centimeters  long. 

They  always  discard  the  runner-stick  for  bars  cast  in  contiguous  pieces. 

The  American  Society  remarks,  without  stating  any  general  laws,  that  the  super- 
ficial crust  found  upon  raw  materials,  either  rolled  or  cast,  is  either  an  advantage  or 
a  hindrance,  according  to  the  work  in  view,  and  should  therefore  be  taken  into  ac- 
count in  the  preparation  of  test-pieces. 

CHAPTER  III. — STUDY  OF  THE  INFLUENCE  OF  TEMPERATURE  UPON  THE 
RESULTS  OF  TESTS. 

Our  resolutions  point  out  the  precautions  to  be  observed  in  making  tests  at  any 
given  temperature,  high  or  low;  afterwards  they  deal  especially  with  tests  made  at 
ordinary  temperatures,  remarking  that  the  influence  of  variations  in  temperature  is 
felt  principally  in  shock  tests,  and  giving  directions  for  the  mitigation  of  the  same. 

The  resolutions  of  the  Conventions  do  not  contain  any  directions  with  regard  to 
those  tests;  they  require  that  in  the  cold  bending  of  copper  bars  the  temperature 
shall  not  be  less  than  10°  C. 

CHAPTER  IV.— STUDY  OF  THE  INFLUENCE  OF  DURATION. 

Our  Commission  gives  no  positive  rule  with  regard  to  the  effect  of  the  duration 
of  test,  considering  that  the  subject  if  not  as  yet  sufficiently  understood;  it  recom- 
mends, however,  the  continuance  of  study  upon  that  subject. 

The  Conventions  declare  for  their  part  that  the  influence  of  time  is  incontestable, 
especially  in  tracing  the  diagrams  in  tensile  tests,  but  they  conclude  that  as  yet  they 
have  not  sufficient  ground  for  establishiug  any  fixed  velocity  of  testing  iron,  copper, 
and  bronze. 

On  the  other  hand,  in  cold-bending  tests  they  claim  that  the  duration  is  of  no 
importance.  In  operating  upon  heated  materials  they  require  that  the  tests  shall  be 
made  as  rapidly  as  possible,  but  this  is  doubtless  in  consideration  of  the  cooling  of 
the  bar. 

The  American  Society  requires  that  the  duration  of  tests  shall  be  noted. 

CHAPTER  V.— GENERAL  OBSERVATIONS  UPON  TESTING  APPARATUS. 

APPARATUS  OPERATING   BY  GRADUAL  ACTION. 

Machines  for  Tensile  Tests. 

The  Conventions  confine  themselves  to  demanding  that  machines  properly  handled 
shall  not  produce  any  shock  on  the  test-pieces.  They  sanction  the  use  of  machines 
operated  by  hydraulic  pressure  or  by  a  screw.  They  add  that  the  test-pieces  should 
be  so  mounted  that  the  strain  of  tension  or  compression  shall  be  uniformly  distribu- 
ted throughout  the  cross-section. 

Besides  those  requirements,  which  coincide  with  those  of  our  Commission,  the 
Conventions  include  in  their  resolutions  more  explicit  directions  as  to  the  mode  of 
fastening  the  test-pieces  for  tensile  tests  than  do  we. 

For  cylindrical  test-pieces  they  propose  the  use  of  spherical  bearings,  preferably 
in  one  piece. 

They  agree  that  test-pieces  of  rectangular  cross-section  shall  be  held  at  each 
extremity  by  a  bolt  passing  through  a  slot  provided  for  the  purpose,  or  that  the  pieces 
shall  be  provided  with  milled  heads  and  clamped  by  proper  wedges. 

They  forbid  positively  the  use  of  the  serrated  wedges  used  by  us,  and  that  point 
should  be  submitted  to  a  renewed  examination  by  us. 


742  APPENDIX. 

This  last  resolution  is  also  adopted  by  the  American  Society,  which,  moreover, 
recommends  in  positive  terms  the  use  of  two  special  types  of  attaching  apparatus  in 
use  in  the  United  States. 

With  regard  to  round  test-pieces  the  American  Society  proposes  to  prolong  the 
cylindrical  section  by  conical  bearings  resting  upon  the  clamping-pieces,  in  prefer- 
ence to  threaded  ends,  such  as  are  often  used.  This  form  is  recommended  for  all 
metals  except  copper  and  its  alloys,  for  which  the  Society  considers  it  as  yet  impos- 
sible to  give  any  standard  type,  conclusive  experiments  being  lacking. 

Machines  for  Pressure  Tests. 

The  Conventions  in  their  resolutions  are  in  almost  perfect  accord  with  us  on  this 
subject.  They  require  that  the  strain  shall  be  carefully  distributed  throughout  the 
cross-section,  and  point  out  that  to  attain  such  a  result  it  is  well  so  to  place  the  pres- 
sure-plates that  at  least  one  may  move  easily  and  freely  in  all  directions. 

Those  resolutions  recommend,  moreover,  the  use  of  very  smooth  test-pieces;  in 
other  words,  those  which  have  been  planed  or  turned;  but  this  recommendation  has 
reference  only  to  the  bearing-surfaces,  since  in  speaking  of  castings  they  require 
besides  that  the  faces  of  test-pieces  for  flexure  and  compression  shall  be  left  in  the 
rough  state. 

The  American  Society  requires  that  the  pieces  to  be  tested  shall  be  placed  in 
position  without  the  aid  of  any  intervening  medium  whatsoever,  such  as  wedges, 
supporting  disks,  etc.,  and  that  they  shall  be  brought  exactly  into  the  axis  of  strain. 
That  society  repeats  that  the  test-pieces  should  be  prepared  with  the  utmost  care, 
the  bearing-surfaces  being  exactly  parallel  and  normal  to  the  axis. 

Whenever  tests  are  made  upon  large  pieces  horizontally  placed  it  is  necessary  to 
take  into  account  the  initial  flexure  due  to  the  weight  of  the  piece  as  held  in  place. 

Machines  for  Transverse,  Folding,  Bending,  and  Curving  Tests. 

The  Conventions  confine  themselves  to  recommending  slow-moving  apparatus, 
acting  either  by  pressure  on  the  middle  between  two  supports  or  by  lateral  pressure 
brought  to  bear  upon  one  part  of  the  test-piece,  while  the  other  is  securely  held  by 
clamping.  Such  apparatus  should  be  simple  and  capable  of  being  used  rapidly. 
The  weakest  part  of  the  test-piece  should  be  clearly  visible. 

For  folding,  they  simply  indicate  that  it  should  be  done  in  a  continuous  manner, 
and  that  if  a  mandrel  is  used  it  should  be  of  the  smallest  possible  diameter,  recom- 
mending in  certain  cases  one  with  a  fixed  diameter  of  25  millimeters.  They  repeat, 
moreover,  that  the  angle  of  bending  is  not  alone  sufficient  to  indicate  the  deforma- 
tion, but  that  the  radius  of  external  curvature  must  be  taken  into  account. 

The  American  Society  recommends  the  use  of  a  very  simple  apparatus  for  making 
bending  tests  upon  mandrels  of  varying  diameter,  and  prescribes  the  use  of  the  hand- 
vise  for  bending,  which  is  accepted  by  us,  however,  with  certain  restrictions. 

For  transverse  tests  that  society  advises  that  supporting  wedges  shall  not  be 
used,  preferring  rolls  that  shall  be  displaced  in  proportion  to  the  deformation  by 
flexure  of  the  bars. 

The  foreign  resolutions  do  not  point  out  the  different  modes  of  testing  by  bend- 
ing that  are  specially  defined  by  our  Commission,  but  the  Conventions  state  that  the 
permanent  committee  should  seek  to  determine,  in  the  comparative  tests  remaining 
to  be  executed,  the  best  method  of  measuring  deformations. 

Machines  for  Torsion.  Tests. 

According  to  our  conclusions,  those  machines  should  be  arranged  in  such  a 
manner  that  the  axis  of  the  piece  will  not  sustain  any  flexure. 

The  resolutions  of  the  Conventions  give  no  data  upon  this  subject,  but  the  Ameri- 
can Society  has  given  definite  instructions  tending  to  prevent  the  production  of  any 
disturbing  strains,  such  as  transversal  flexure  or  longitudinal  tension  over  and  above 
torsion  properly  so  called.  To  this  end  the  collars  which  hold  the  test-pieces  should 
be  exactly  concentric  with  it,  to  avoid  giving  any  but  a  tangential  strain. 


UNIFORM  METHODS  OF  TESTING  METALS.  743 


APPARATUS  OPERATING  BY   ABRUPT  ACTION. 

The  resolutions  of  the  Conventions  are  generally  in  harmony  with  ours  in  princi- 
ple, but  they  give  much  more  explicit  directions  for  the  setting  up  of  testing-ham- 
mers, especially  in  the  case  of  heavy  machines  intended  to  test  whole  pieces.  They 
have  adopted  for  this  purpose,  as  a  standard  type  of  hammer,  one  weighing  1000 
kilograms,  permitting  in  certain  exceptional  cases  the  use  of  one  weighing  only  500 
kilograms,  and  they  have  decided  that  every  hammer  of  the  standard  type  shall  be 
stamped  and  officially  registered.  They  require  that  the  studies  relating  to  the  ques- 
tion of  shock  tests  shall  continue,  and  they  have  charged  the  permanent  committee 
with  collecting  all  new  propositions  relating  to  the  installation  of  machines  for  shock 
tests. 

They  accept  hammers  as  we  make  them,  of  cast  iron  or  forged  steel ;  they  add 
that  the  striking-surface  should  be  of  forged  steel,  finished  by  dovetailing  and  made 
secure  by  wedges  in  such  a  manner  that  the  vertical  centre  of  gravity  of  the  whole 
may  not  be  disturbed. 

This  vertical  should  coincide  with  the  axis  of  the  leads  and  should  be  indicated 
by  marks  upon  the  anvil  or  the  anvil-block.  The  proper  arrangement  of  the  striking- 
surface  should  be  verified  by  means  of  suitable  reference-points. 

We  require,  moreover,  that  the  mass  and  shape  of  the  hammer  shall  be  perfectly 
symmetrical  with  respect  to  the  plane  of  the  leads. 

Our  directions,  more  especially  with  reference  to  tests  upon  test-pieces,  regulate 
the  form  of  the  face  of  the  small  hammers  used,  and  they  indicate  even  the  radius 
of  curvature  to  be  given  that  face,  depending  on  the  kind  of  metal  to  be  tested. 
They  also  give  the  different  weights  for  such  hammers  used  under  similar  circum- 
stances. 

According  to  the  resolutions  of  the  Conventions,  the  guided  length  of  the  hammer 
should  be  at  least  double  the  clear  width  between  the  guides  ;  we  claim,  however, 
only  that  it  should  be  greater  than  the  width  between  the  guides. 

The  Conventions  require  that  the  weight  of  the  anvil-block  shall  be  at  least  ten 
times  that  of  the  hammer,  and  that  the  foundations  shall  be  inelastic.  We  require 
that  the  anvil  block  shall  constitute,  either  alone  or  embedded  in  solid  masonry,  a 
solid  mass  from  fifteen  to  twenty  times  heavier  than  the  hammer. 

In  the  working  of  the  detaching  apparatus  the  Conventions  agree  with  us  that 
there  should  be  no  wedging.  The  Conventions  advise  the  placing  of  the  point  of 
suspension  upon  the  same  vertical  as  the  centre  of  gravity  of  the  hammer,  and  to 
insert  between  the  detaching  device  and  the  hammer  a  short  flexible  piece — for  ex- 
ample, a  chain  or  cord.  They  point  out  as  a  style  to  be  recommended  the  detaching 
device  adopted  in  Russia,  which,  however,  from  the  sketch  given,  does  not  seem  to 
be  provided  with  an  intermediate  chain  or  cord 

In  regard  to  the  friction  on  the  leads,  they  recommend  that  thoSe  leads  should 
be  lubricated  with  plumbago.  They  reject  all  apparatus  having  a  work  duo  to  fric- 
tion greater  than  2  per  cent  of  the  usual  work.  They  describe  a  process  of  measur- 
ing friction  by  inserting  a  spring-balance  between  the  hammer  and  its  lifting-rope. 
They  propose  to  deduce  the  effective  weight  of  the  hammer  from  the  effect  produced, 
with  a  given  height  of  fall,  on  a  centrally  mounted  standard  cylinder  made  of  copper, 
of  dimensions  yet  to  be  determined. 

For  the  height  of  fall  they  advise  that  6  meters  shall  not  be  exceeded,  as  the  set- 
ting up  of  hammers  of  greater  height  cannot  be  done  with  as  much  security  or  ex- 
actitude. They  recommend  the  use  of  a  sliding  scale  for  measuring  the  effective 
work,  so  that  the  zero  of  the  graduation  may  be  set  at  the  top  of  the  piece  to  be 
tested.  That  scale  should  be  divided  into  metric  half-tons.  (See  Fig.  306,  p.  378.) 

All  of  the  recommendations  of  the  Conventions  with  regard  to  the  setting  up  of 
machines  for  shock  tests  are  agreed  to  by  the  American  Society  ;  the  weight  of  the 
hammer  and  the  height  of  fall  are  determined  by  the  measures  in  use  in  America. 
The  weights  adopted  are,  respectively',  1000,  1500,  and  2500  pounds  for  testing  large 
pieces  (equal  to  453,  653,  and  907  kilograms),  and  the  height  of  fall  is  fixed  at  20 
feet  (equal  to  6.09  meters),  allowing,  however,  without  doubt,  the  adoption  of  a  less 
height  of  fall  in  special  cases.  (See  standard  adopted  by  the  National  Car-builders' 
Assoc'n,  p.  379.) 


744  APPENDIX. 

• 
CHAPTER  VI.— EXAMINATION  OF  THE  FORCES  TO  BE  MEASURED. 

Our  resolutions  recommend  in  effect  that  the  strains  and  deformations  produced 
in  all  tests  by  continuous  action  shall  be  measured ;  these  form  of  necessity  two 
great  classes — the  one  of  elastic  and  the  other  of  permanent  deformation. 

Concerning  the  period  of  elastic  deformation,  three  limits  of  elasticity  are  dis- 
tinguished and  defined,  viz.,  the  theoretical,  the  proportional,  and  the  apparent. 
Concerning  the  period  of  permanent  deformation,  our  resolutions  define  the  maxi- 
mum load  supported,  and  the  load  of  rupture,  properly  so  called,  giving  the  defor- 
mation corresponding  to  each  of  those  two  loads. 

Neither  the  resolutions  of  the  Conventions  nor  those  of  the  American  Society 
give  any  instructions  common  to  all  tests  made  by  gradual  action;  they  restrict 
themselves  entirely  to  tensile  tests. 

The  Conventions  require  that  during  the  elastic  period  there  shall  be  sought  the 
yield-point  and  the  limit  of  proportional  elongation,  appearing  at  the  same  time  to 
admit  that  those  two  limits  are  blended,  and  during  the  period  of  permanent  defor- 
mation the  maximum  resistance  and  the  beginning  of  contraction  as  well  as  the 
load  of  actual  rupture  with  the  corresponding  section. 

The  American  Society  requires  the  determination  of  the  same  information, 
excepting  only  the  beginning  of  contraction,  insisting  especially  upon  the  impor- 
tance of  the  yield- point,  which  measurement  it  claims  should  be  made  with  the 
greatest  precision. 

It  defines  that  limit  as  being  the  load  which  produces  a  modification  in  the  rate 
of  elongation,  which  would  seem  to  identify  it  with  the  proportional  limit ;  but 
farther  on,  in  an  annexed  illustration,  it  requires  that  the  limit  shall  be  determined 
by  noting  the' point  at  which  the  elongation  is  suddenly  augmented,  which  brings 
us  back  to  the  apparent  limit. 

The  recommendations  of  that  society  prescribe,  moreover,  the  measurement  of 
the  elastic  elongation  with  a  view  of  determining  thereby  the  modulus  or  coefficient 
of  elasticity,  and  they  point  out,  to  this  end,  a  special  process  consisting  of  measur- 
ing the  elongations  between  certain  limiting  loads,  determined  in  advance. 

They  also  observe  the  smallest  section  of  the  test-piece  under  the  action  of  the 
elastic  limit  (yield-point),  and,  after  the  test,  the  section  of  rupture. 

In  the  calculation  of  the  strain  brought  to  bear  upon  the  unit  of  section,  their 
resolutions  add  that  it  is  necessary  always  to  consider  the  initial  appearance  of  the 
test-piece,  and  not  the  constantly-changing  appearance  under  the  different  loads 
that  it  supports  up  to  the  limit  of  rupture. 

This  resolution  conforms  with  that  of  our  Commission.  /lowever,  as  in  experi- 
ments made  upon  copper  and  brass,  a  comparison  of  the  xoads  developed  in  the 
course  of  the  tests  with  the  corresponding  deformations  has  given  rise  to  interesting 
conclusions  ;  our  Commission  has  expressed  the  hope  that  analogous  studies  shall 
be  made  in  regard  to  iron  and  steel. 

CHAPTERS  VII  AND  VIII.— MECHANICAL  AND  TECHNICAL  TERMINOLOGY. 

Those  two  questions  have  been  examined  by  our  Commission  only,  but  we  have 
not  been  able  to  establish  any  fixed  laws  in  regard  to  them.  They  have  not  been, 
considered  by  either  the  Conventions  or  by  the  American  Society. 

FOURTH  PART. 

DETAILED  STUDY  OF  THE  DIFFERENT  METHODS  OF  TESTING. 
FIRST  CLASS.— METHODS  OF  TESTING  BY    GRADUAL  ACTION. 

Our  Commission  states  in  a  general  way  that  those  tests  should  be  made  in  s 
manner  as  continuous  and  as  regularly  progressive  as  possible,  and  that  recom 
mendation  is  in  accord  with  that  adopted  by  the  Conventions  with  regard  to  tensil< 
tests. 

The  American  Society  agrees  to  this  also  in  a  general  way,  but  it  provides  fo 
stopping  the  strain  at  certain  intervals,  whenever  it  is  necessary  to  make  observa 


UNIFORM  METHODS  OF  TESTING  METALS.  745 

tions  of  deformation,  which  is  the  case,  for  instance,  in  measuring  the  elastic  limit 
and  the  elastic  elongation.  The  Society  requires  in  such  cases  that  the  developed 
strain  shall  never  be  diminished,  but  that  it  shall  be  maintained  continuously  in 
action. 

CHAPTER  I.— TENSILE  TESTS. 

MEASURE   OF   STRESS   AND   ELONGATION. 

Our  resolutions  define  the  precision  to  be  sought  in  the  definition  and  scientific 
observation  of  the  first  two  elastic  limits  previously  described  ;  they  point  out  tlnit 
for  such  purpose  the  elongations  should  be  measured  to  the  nearest  thousandth  of  a 
millimeter. 

Such  precision  is  unnecessary  for  the  determination  of  the  third  limit,  called  the 
apparent  limit,  or  the  beginning  of  great  deformation  under  a  constant  load. 

Regarding  the  observations  made  during  the  period  of  permanent  deformation, 
our  Commission  recommends  that  the  maximum  load  that  can  be  borne  shall  be 
measured,  saying  that  it  does  not  appear  to  be  necessary  to  measure  the  load  of  rup- 
ture, while,  as  has  been  shown  heretofore,  this  measurement  is  required  by  the 
Conventions  and  by  the  American  Society. 

In  regard  to  measuring  elongation,  our  Commission  believes  that  for  current 
practical  tests  on  products  of  the  same  well-known  make  it  is  sufficient  generally  to- 
measure  the  total  elongation  after  rupture;  but  in  more  exact  tests  it  would  be  use- 
ful to  make  some  special  experiments  with  a  view  to  determining  the  relative  value  of 
the  different  parts  which  compose  the  total  elongation  (distributed  elongation  and 
elongation  of  contraction). 

The  foreign  resolutions  do  not  consider  this  distinction.  They  recommend 
simply  a  method  of  measuring  the  total  elongation  suitable  for  reducing  the  results 
to  uniformity  by  disregarding  the  influence  that  the  position  of  the  section  of  rupture 
beyond  the  middle  third  of  the  test-piece  may  have  upon  the  observed  elongation. 
This  method  amounts  in  principle  to  doubling  the  measured  elongation  for  a  distance 
equal  to  one  half  the  length  of  the  test-piece,  counting  from  the  section  of  rupture 
on  the  side,  where  it  is  possible  to  measure  it,  in  such  a  manner  as  to  render  the 
same  conditions  as  would  have  obtained  had  the  rupture  occurred  in  the  middle  of 
the  test-piece  and  had  the  elongation  been  produced  freely  on  both  sides.  The  result 
is  to  increase  a  little  the  effective  elongation  measured  directly  on  the  real  test-piece. 
This  method  is  inconvenient  in  that  it  is  necessary  in  advance  to  divide  the  use- 
ful or  test  length  into  very  small  sections.  The  length  of  each  section  is  fixed  at  1 
centimeter  in  Germany  and  at  a  half  or  even  a  quarter  of  an  inch  in  America  (12  or 
6  millimeters).  As  the  elongations  during  the  course  of  the  test  are  produced  in  a 
comparatively  irregular  manner  upon  the  length  of  the  test-piece,  we  may  consider 
that  they  are  not  necessarily  uniform  at  the  ruptured  section  even  when  that  is  in 
the  middle  of  the  piece,  and  the  method  can  give  in  this  respect  only  approximate 
results. 

It  is  true  that  if  recourse  to  that  method  is  not  desired  it  will  be  found  necessary, 
according  to  our  resolutions,  to  discard  every  test-bar  whose  elongation  of  contrac- 
tion is  not  integrally  included  between  the  reference-points ;  the  resolutions  of  the 
Conventions,  particularizing  still  further,  give  this  same  in  junction  when  the  section 
of  rupture  falls  beyond  the  "middle  third  of  the  gauged  length. 

In  regard  to  tensile  diagrams,  our  resolutions  declare  that  it  does  not  seem 
necessary  to  have  recourse  to  them,  at  least  in  current  practical  tests  with  a  view  to 
ascertaining  the  quality  of  the  metal  tested  from  a  determination  of  the  useful  sur- 
face they  present. 

The  resolutions  of  the  Conventions  provide,  however,  for  the  use  of  diagrams, 
and  require  that  their  area  shall  be  calculated  up  to  the  limit  corresponding  to 
rupture.  They  observe  on  this  subject  that  without  doubt,  in  principle,  the  work 
on  the  test-piece  should  be  considered  only  up  to  the  beginning  of  contraction,  but 
that  in  most  cases  the  work  corresponding  to  that  last  period  is  of  little  importance, 
and  the  error  thus  produced  cannot  be  very  considerable.  In  cases  where  the 
diagram  is  not  made  by  special  apparatus,  they  advise  making  as  many  observations 
as  possible  during  the  test  in  order  to  trace  the  diagram  by  separate  points. 


746  APPENDIX. 

The  resolutions  of  the  American  Society  also  provide  for  the  use  of  such 
diagrams. 

With  regard  to  the  varying  coefficients  thus  far  proposed,  our  Commission  finds 
it  impossible  to  recommend  them,  and,  moreover,  the  foreign  resolutions  make  no 
mention  of  them. 

In  regard  to  the  precision  to  be  sought  in  measuring  strains  and  elongations,  our 
Commission  declares  that  for  strains  less  than  5000  kilograms  a  determination  to 
within  25  kilograms  is  sufficient,  going  up  to  the  limit  of  50  kilograms,  when  the 
strain  exceeds  5  tons ;  or,  for  the  first  class,  to  within  one  two-hundredth,  and  for 
the  second  to  within  less  than  one  one-hundredth  of  the  total  sum. 

The  Conventions  state  that  on  their  part  they  will  accept  an  error  of  one  tenth 
of  a  kilogram  per  square  millimeter  for  tensile  strains  corresponding  to  the  elastic 
limit  (yield-point)  and  to  that  of  rupture,  which  leads  in  practice,  especially  for  the 
load  of  rupture,  to  a  much  smaller  proportion  of  error  than  we  have  permitted. 

The  American  Society  makes  no  recommendation  upon  this  subject. 

In  measuring  the  dimensions  of  test-pieces  and  elongations  our  Commission  rec- 
ommends a  determination  to  within  five  one-hundredths  of  a  millimeter  in  the  case 
of  dimensions  equal  to  or  less  than  10  millimeters,  and  it  accepts  an  approximation 
to  within  one  tenth  only  when  the  length  to  be  measured  is  greater  than  10  milli- 
meters ;  the  limit  is,  therefore,  to  within  more  than  five  one-thousandths  in  the  first 
case,  and  to  within  less  than  one  one-hundredth  in  the  second. 

The  resolutions  of  the  Conventions  recommend  a  degree  of  precision  reaching  one 
one-thousandth  in  measuring  the  elongation  of  rupture,  and  of  one  one-hundredth 
in  measuring  the  contraction  of  area  (considered,  no  doubt,  as  being  the  section  of 
rupture  itself). 

They  recognize,  however,  that  in  many  cases  these  decimals  are  uncertain,  and 
that  it  is  not  necessary  to  add  others.  They  state  that  it  is  sufficient  to  take  the 
dimensions  of  test-pieces  to  within  one-tenth  of  a  millimeter,  which,  considering 
the  measurement  of  the  thickness  and  the  width  of  the  section,  gives  a  degree  of 
precision  inferior  to  that  recommended  by  our  Commission. 

They  require  that  the  elongation  shall  be  measured  on  two  diametrically  opposed 
sides  of  the  test-bar,  in  order  that  the  mean  may  be  taken  of  the  sum.  of  the  lengths 
obtained  by  measuring  upon  each  part  respectively  the  distance  comprised  between 
the  corresponding  reference- point  and  the  section  of  rupture. 

For  rectangular  test-pieces  it  is  even  proposed  to  make  three  measurements  of 
elongation,  taking  them  upon  the  two  sides  and  upon  one  of  the  faces.  The  mean  of 
the  first  two  measures  should  be  given  and  the  last  one  should  be  stated  separately. 

The  General  Report  of  our  Commission  only  mentions  the  use  of  elasticimeters, 
which  are  considered  almost  indispensable  in  determining  the  elastic  limit  (yield- 
point),  but  which  seem  less  necessary  for  the  simple  measurement  of  the  total 
elongation. 

With  the  aim  of  measuring  the  section  of  rupture  with  all  possible  precision  our 
resolutions  propose  that  the  measurement  of  the  dimensions  shall  always  be  made  at 
two  opposite  points,  and  that  there  shall  be  considered  either  the  circle  of  mean 
diameter,  or  the  rectangle  of  mean  dimensions,  according  as  the  test-pieces  have 
circular  or  rectangular  sections. 

DIMENSIONS   OF  TEST-PIECES. 

In  order  that  the  proximity  of  the  heads  shall  not  interfere  with  the  observed 
results,  especially  in  the  measurement  of  elongation,  our  resolutions  require  that 
the  distance  from  the  springing  or  end  of  the  heads  to  the  reference-points  must  be 
equal  at  least  to  the  diameter  or  to  the  greater  side  of  the  transverse  section  of  the 
test-piece ;  they  consider  that  under  such  conditions  the  form  of  the  heads  is  not 
important. 

The  Conventions  limit  themselves  to  remarking  that  for  cylindrical  test-pieces  the 
actual  length  of  the  cylindrical  part  should  exceed  the  test  length  by  at  least  10 
.millimeters,*  which  may  be  interpreted,  doubtless,  as  imposing  a  uniform  minimum 

*  The  original  resolutions  require  that  the  actual  length  shall  exceed  the  test  length  by  20  milli- 
meters.—O.  M.  C. 


UNIFORM  METHODS  OF  TESTING  METALS.  747 

of  5  millimeters  of  waste  length  at  each  end,  regardless  of  the  diameter  of  the  test- 
piece,  which  may  be  10,  15,  20,  or  25  millimeters. 

The  American  Society  gives  regulations  analogous  to  those  of  the  French  Com- 
mission. It  requires  that  with  round  test-pieces  the  distances  reserved  bevond  each 
reference-point  shall  be  equal  to  or  greater  than  a  diameter.  For  flat  or  built-up 
square  test-pieces  its  regulations  require  once  and  a  half  the  width  of  the  section  or 
the  side  of  the  square. 

In  order  to  make  a  comparison  of  the  total  elongations,  taken  after  the  rupture 
of  circular  test-pieces  of  different  design,  our  Commission  has  decided  to  establish  a 
fixed  relation  between  the  transverse  section  and  the  useful  or  test  length  of  the 
test-piece.  This  relation,  deduced  by  the  law  of  similarity,  shows  that  the  test 
length  should  be  proportional  to  the  square  root  of  the  cross-section,  and  that  fun- 
damental law  has  been  admitted  also  by  the  Conventions.  The  only  difference  is  in 
respect  to  the  value  of  the  coefficient  adopted. 

While  our  formula 

r  =  66.674, 

or          I  =    8.18  4/1, 

resutls  in  giving  a  diameter  of  27.64  millimeters  to  a  test-piece,  having  a  test  length 
of  200  millimeters,  the  formula  of  the  Conventions, 

i  =  11.3  t/1, 

leads  to  a  smaller  diameter  for  the  same  test  length,  for  it  gives  in  fact  a  diameter 
of  20  millimeters  to  a  test-piece  200  millimeters  long.  In  a  general  way  this  formula 
recommends  itself  on  account  of  its  great  simplicity,  inasmuch  as  the  calculation  of 
the  linear  dimensions  is  immediate;  the  useful  or  test  length  amounting  always  to 
ten  times  the  diameter. 

Our  formula  presents,  on  the  other  hand,  the  advantage  of  expressing  the  area 
by  a  simple  number,  for  example,  600  square  millimeters  for  a  test-piece  200  milli- 
meters in  length,  considering  that  it  is  better  to  seek  simplicity  in  expressing  the 
cross-section—rather  than  in  indicating  the  diameter,  because,  no  matter  what 
number  expresses  the  diameter,  the  difficulty  of  measuring  it  is  always  the  same, 
whereas  it  is  only  the  section  which  intervenes  in  the  calculations,  and  the  adoption 
of  a  simpler  number  to  express  the  section  greatly  facilitates  such  calculations. 

Notwithstanding  the  employment  of  the  law  of  similarity,  the  two  resolutions 
preserve  well-defined  normal  types,  to  which  they  recommend  that  reference  be  made. 
These  are  four  in  number  in  the  two  cases. 

Our  standards  have,  respectively,  test  lengths  of  70,  100,  141,  and  200  milli- 
meters ;  cross-sections  of  75,  150,  300,  and  600  square  millimeters,  and  diameters  of 
9.77,  13.82,  19.55,  and  27.64  millimeters.  The  standards  of  the-  Conventions  give 
sections  very  closely  resembling  these,  but  their  longitudinal  dimensions  are  greater; 
they  have  lengths,  respectively,  of  100,  150,  200,  and  250  millimeters  for  diameters 
of  10,  15,  20,  and  25  millimeters. 

Those  standard  types  are  adopted  for  steel  and  iron,  as  well  as  for  copper  and  its 
alloys ;  for  castings,  however,  the  Conventions  prescribe  test-pieces  having  a  diam- 
eter of  25  millimeters,  and  a  useful  or  test  length  of  200  millimeters. 

The  American  Society  prescribes  four  standards  with  diameters,  respectively,  of 
0.4,  0.6,  0.8,  and  1  inch,  which  equals  0.010,  0.015,  0.020,  and  0.025  millimeter,  but 
it  preserves  a  constant  useful  or  test  length  of  8  inches  (0.2)  meter,  ignoring  the 
differences  which  must  occur  in  the  measurement  of  total  elongation  by  testing  with 
a  uniform  length  and  a  variable  diameter. 

The  test  length  of  8  inches,  as  well  as  the  various  diameters  given,  have  been 
chosen,  moreover,  for  the  purpose  of  approaching  as  nearly  as  possible  the  measures 
of  the  metric  system,  counting  8  inches  as  equal  to  200  millimeters.  This  is  ex- 
pressly stated  by  the  Society  itself. 

The  law  of  similarity  thus,  admitted,  as  has  been  shown,  for  cylindrical  test- 
pieces,  is  extended  by  our  Commission,  with  the  same  coefficient,  to  test-pieces  of 


748  APPENDIX. 

-square  cross-section,  and  even  to  pieces  that  are  simply  rectangular,  observing  care- 
fully certain  restrictions  established  with  a  view  to  facilitate  manufacture,  by  estab- 
lishing different  series,  in  each  one  of  which  the  width  remains  the  same. 

The  Conventions  also  extend  the  formula  expressing  the  law  of  similarity  to  test- 
pieces  of  simply  rectangular  cross-section,  but  without  introducing  any  definite 
restrictions.  They  recommend,  however,  that  the  section  30  by  10  shall  be  consid- 
ered as  the  standard,  even  when  the  breadth  and  thickness  may  be  chosen  at  pleas- 
ure. 

When  the  thickness  is  given,  as  for  plates,  and  when  it  does  not  exceed  24  milli- 
meters, a  width  of  30  millimeters  should  be  adopted. 

Whenever  the  thickness  exceeds  24  millimeters  it  should  be  considered  as  breadth, 
and  a  thickness  of  10  millimeters  should  be  given  to  the  test-piece. 

When  the  testing-machines  are  not  sufficiently  powerful,  the  limit  of  24  millimeters 
should  be  replaced  by  that  of  16  or  17  millimeters. 

The  American  Society  permits  on  its  part  a  width  of  1.2  inches  (0.030  meter)  for 
rectangular  test-pieces  having  a  thickness  of  less  than  1  inch  (0.025  meter). 

If  the  thickness  reaches  1  inch,  the  measure  of  0.8  inch  (0.02  meter)  will  be  taken 
for  the  width. 

In  testing  sheets  and  plates  the  crust  produced  in  rolling  should  not  be  removed. 

In  testing  sheets  there  should  be  taken  two  samples  having  the  total  section  of  the 
bar. 

Besides  the  preceding  rules  just  given,  which  are  considered  applicable  only  to 
rectangular  test-pieces  having  a  thickness  of  more  than  5  millimeters,  our  Commis- 
sion has  adopted  special  dimensions  for  test-pieces  having  a  thickness  of  less  than  that 
figure,  considering  that  it  is  not  necessary  to  be  guided  by  the  law  of  similarity,  be- 
cause that  law  is  doubtless  no  longer  applicable  in  such  a  case. 

The  useful  or  test  length  of  those  thin  test-pieces  has  been  fixed  uniformly  at  100 
millimeters,  without  reference  to  the  thickness  or  the  nature  of  the  metal  to  be  tested. 

CONDUCT   OF  TESTS. 

Our  resolutions  recommend,  as  has  been  indicated,  operating  by  progressive  or 
gradual  tension.  This  recommendation  is  also  found  in  the  resolutions  of  the  Con- 
ventions, but  the  American  Society  permits  interruption  of  the  test,  without  reliev- 
ing, however,  the  action  of  the  strain,  for  the  purpose  of  making  certain  important 
observations  during  the  course  of  the  test,  such  as  those  relating  to  the  elastic  limit 
(yield-point). 

In  general,  the  American  Society  recommends  the  utmost  care  in  placing  the  test- 
pieces,  so  that  they  may  be  directly  in  the  axis  of  the  machine,  and  to  this  end  it 
advises  that  it  should  be  referred  carefully  to  two  normal  planes  intersecting  each 
other  in  line  with  this  axis. 

The  Society  also  recommends  placing  test-pieces  for  tensile  tests  under  a  very 
slight  initial  strain  (from  0.7  to  1.4  kilograms  per  square  millimeter)  before  com- 
mencing observations,  in  order  that  the  errors  generally  made  at  the  beginning  of  a 
test  may  be  avoided. 

In  regard  to  the  rate  of  testing,  our  Commission  has  confined  itself  to  giving  some 
approximate  directions,  and  it  observes,  to  that  end,  that  the  duration  of  a  test, 
which  should  be  in  a  certain  measure  a  function  of  the  volume  of  the  test-piece, 
should  be  comprised  between  one  and  six  minutes  for  current  tests  on  test-pieces  of 
ordinary  dimensions.  This  time  may  be  reduced  to  thirty  seconds  for  small  test- 
pieces  having  a  thickness  of  less  than  5  millimeters.  Care  should  be  taken,  espe- 
cially with  soft  metals,  to  avoid  heating  the  bars. 

The  foreign  resolutions  make  no  recommendations  upon  this  subject.  The  Con- 
ventions, however,  observe  that  in  establishing  the  diagram  of  tensile  test  great 
importance  should  be  attached  to  showing  with  what  rapidity  the  diagram  was 
traced. 


UNIFORM  METHODS  OF  TESTING  METALS.  749 

CHAPTER  II.— PRESSURE  TESTS. 

TESTS   ON   SHORT   PIECES. 

For  determining  the  elastic  limit  our  Commission  advises  the  employment  of 
•cylindrical  test-pieces  having  a  diameter  of  27.65  millimeters  (600  square  millimeters 
in  cross-section)  and  100  millimeters  of  useful  or  test  length;  but  for  the  determi- 
nation of  the  maximum  resistance  to  compression  or  crushing  the  diameter  of  the 
standard  test-pieces  will  be  reduced  to  19.56  millimeters  (300  square  millimeters  of 
cross-section),  and  the  useful  length  to  20  millimeters. 

The  regulations  of  the  Conventions  propose  in  testing  castings  the  use  of  cubes  of 
25  millimeters  a  side,  making  them  serve  as  samples  for  pressure-tests.  In  another 
passage,  however,  they  recommend  a  height  of  30  millimeters. 

They  give  no  complementary  information  on  the  subject  of  that  test,  merely  stat- 
ing that  Wachler  adopted  25  millimeters  as  the  standard  dimension  in  his  studies. 

The  American  Society  considers  that  pressure  tests  upon  short  test-pieces  are  of 
little  interest,  recommending,  preferably,  the  adoption  of  pieces  of  a  length  of  from 
10  to  20  diameters. 

However,  when  it  is  a  question  of  determining  the  resistance  to  disaggregation, 
the  use  of  cylinders  1  inch  in  diameter  (0.025  meter)  and  2  inches  in  height  (0.050 
meter)  is  proposed.  Whenever  the  elastic  resistance  is  to  be  determined  the  height 
will  be  increased  to  10  or  20  inches  (0.254  meter  or  0.508  meter),  always  keeping  the 
useful  or  test  length  at  8  inches,  as  in  tensile  tests. 

TESTS   ON   LONG  PIECES   (FLAMBEMENT). 

Our  Commission  insists  especially  upon  the  interest  of  making  buckling  tests, 
stating  that  for  iron  and  steel  the  resistance  determined  by  the  tests  thus  made  is  in 
no  way  proportional  to  that  determined  by  tensile  tests,  and  in  the  existing  state  of 
science  cannot  be  deduced  from  the  results  obtained  by  the  usual  tests. 

The  Commission  declares  that  the  tests  can  be  made  on  riveted  pieces  or  on  bars 
cut  up  for  this  purpose,  and  it  observes  that  to  render  the  two  tests  comparable  it  is 
sufficient  that  the  ratio  of  the  length  of  the  test-piece  to  the  minimum  radius  of 
gyration  of  the  section  should  have  the  same  value.  In  tests  upon  test-pieces  the 
Commission  proposes  to  give  to  that  ratio  values  which  are  multiples  of  5  or  10. 

It  recommends  that  those  tests  shall  always  be  made  under  well-defined  condi- 
tions, such  as  those  by  perfect  hinging  or  complete  clamping.  The  precautions  to  be 
observed  in  the  first  case  are  prescribed,  but  it  is  added  that  no  satisfactory  disposi- 
tion for  such  testing  by  clamping  is  yet  known. 

The  foreign  resolutions  give  no  particular  instructions  regarding  pressure  tests 
on  long  pieces.  However,  the  American  Society  provides  for  tests  upon  pieces 
having  a  diameter  of  1  inch  and  from  10  to  20  inches  long  for  determining  the  elastic 
limit  (yield-point). 

It  requires  that  the  process  shall  be  the  same  as  in  tensile  tests,  dividing  the 
useful  or  test  length  into  small  sections  in  such  a  manner  that  the  loss  in  value 
sustained  may  be  determined  from  its  elements,  and  that  the  calculation  of  the 
modulus  and  the  coefficient  of  elasticity  shall  be  made  under  like  conditions. 

CHAPTER  III.— TRANSVERSE  TESTS. 

TESTS  ON  TEST-PIECES. 

astings. 

Our  Commission  adopts  for  standard  bars  a  section  having  a  side  of  40  milli- 
meters, indicating  that  the  total  length  should  be  determined  in  such  a  manner  as  to 
give  a  useful  or  test  length  of  150  or  500  millimeters  according  to  the  apparatus  used 
(Monge  or  Joessel  balance) 

The  Conventions  have  adopted  a  prism  3  centimeters  on  a  side,  with  a  total 
length  of  110  centimeters,  giving  a  useful  or  test  length  of  100  centimeters.  They 


750  APPEND! 

recommend  measuring  the  resistance  to  flexure  up  to  the  point  of  rupture  and  the 
corresponding  work  on  three  test-pieces.  The  faces  of  the  pieces  should  be  left  in 
their  rough  condition. 

Our  Commission  prescribes  that  the  faces  of  the  bars  shall  be  shaped  by  a  machine 
and  the  edges  rounded  by  a  file.  It  regulates  finally  the  duration  of  the  test,  which 
should  be  comprised  between  one  and  two  minutes. 

The  American  Society  requires  for  scientific  tests  that  the  effect  of  superficial 
quenching  shall  be  avoided  by  using  bars  measuring  at  least  2  inches  on  a  side 
(0.050  meter)  or  2i  inches  in  diameter  (0.063  meter).  In  current  practical  tests 
there  will  be  used  bars  measuring  only  1  inch  (0.025  meter)  on  a  side,  taking  the 
necessary  precaution  to  throw  aside  surfaces  which  have  been  hardened  or  marked 
with  blow-holes. 

Steel  Plates  for  Springs. 

Our  Commission  fixes  the  length  to  be  adopted  for  developed  test  bars  at  1  meter, 
the  section  to  be  used,  however,  being  preserved  without  any  modification. 

The  plate  will  be  prepared  under  the  same  conditions  as  to  quenching  and 
annealing  as  the  springs. 

For  testing,  it  will  be  placed  on  two  movable  slides,  the  use  of  which  is  also  rec- 
ommended by  the  American  Society. 

The  test  will  be  continued  without  stopping  or  lessening  the  load  and  with  a 
regular  and  continuous  movement  up  to  the  limit  fixed  upon,  in  such  manner  that 
the  duration  of  the  whole  test  is  comprised  between  two  and  five  minutes. 

The  foreign  recommendations  contain  no  special  remarks  upon  that  subject. 

The  American  Society  recommends,  however,  in  a  general  way,  regarding  trans- 
verse tests,  that  the  sample  should  be  placed  firmly  in  a  horizontal  position  to  avoid 
supporting  wedges,  that  the  strain  shall  be  brought  to  bear  exactly  in  the  middle  and 
normal  to  the  axis  of  the  piece,  and  in  a  plane  passing  through  the  three  strained 
points.  It  requires  that  the  bars  used  shall  be  1  inch  (0.025  meter)  on  a  side,  have 
a  length  of  40  inches  (1.016  meters),  and  that  they  shall  be  placed  upon  supports  36 
inches  apart  (0.914  meter). 

According  to  the  resolutions  of  the  Society,  the  deviations  should  be  measured 
from  a  fixed  and  invariable  base.  It  is  well  to  determine  them  at  points  situated  at 
stated  intervals  from  the  middle  of  the  bar  in  such  a  manner  as  to  obtain  certain 
elements  of  the  curve  of  flexure  over  the  whole  extent  of  the  length,  and  especially 
in  the  vicinity  of  the  elastic  limit  (yield-point). 

Certain  values  of  the  permanent  deviation  may  also  be  determined. 

TESTS   ON   FINISHED   OR  WHOLE   PIECES. 

Springs  of  Parallel  and  Spiral  Plates. 

Our  Commission  recommends  in  transverse  tests  that  springs  be  subjected  to  a 
less  strain  than  that  which  corresponds  to  permanent  deformation. 

The  American  Society,  on  its  part,  proposes  to  apply  the  maximum  working  load 
and  to  determine  the  deviation  produced  by  that  test.  The  test  load  will  be  obtained 
by  proceeding  by  pressure  or  by  shock,  according  to  circumstances,  but  it  will  be 
applied  only  once. 

Rails  and  Fish-plates. 

Our  Commission  recommends  determining  as  nearly  as  possible  the  load  cor- 
responding to  the  proportional  limit  of  elasticity  in  testing  those  pieces;  it  adds  that 
the  duration  of  the  tests  should  be  comprised  between  two  and  five  minutes. 

The  foreign  resolutions  examine  also  the  question  of  transverse  tests  by  static 
pressure,  requiring  that  they  shall  be  considered  from  the  two  following  points  of 
view  :  First,  there  will  be  determined  the  elastic  limit  (the  point  where  the  set  be- 
comes permanent) ;  second,  there  will  be  measured  the  flexibility  under  increasing 
loads,  exceeding  even  the  elastic  limit. 

The  American  Society  states  that  it  is  hardly  practicable  to  subject  either  rails  or 
axles  to  a  transverse  test  by  static  pressure. 


UNIFORM  METHODS  OF  TESTING  METALS.  751 


CHAPTER  IV.— FOLDING,  BENDING,  AND  CURVING  TESTS. 

Our  Commission  proposes  to  adopt  for  those  tests  standard  bars  40  millimeters 
wide  and  250  millimeters  long,  observing  that  the  length  may  be  reduced  to  150 
millimeters  for  copper  and  its  alloys.  It  recommends,  besides,  that  those  various 
tests  shall  be  made  by  a  machine  so  arranged  as  to  produce  a  slow  progressive 
strain,  and  that  in  folding  tests  the  initial  fold  shall  be  obtained  with  a  radius  of 
curvature  differing  as  little  as  possible  from  that  exacted  for  the  limiting  fold. 

For  mechanical  folding  the  use  of  the  hydraulic  press  or  hammer  is  recommended. 

Our  Commission  gives,  besides,  certain  directions  for  folding  done  by  a  hand- 
vise.  It  is  necessary  to  observe  here  that  this  mode  of  testing  is  prohibited  by  the 
American  Society. 

In  regard  to  bending  tests,  our  Commission  has  not  yet  fixed  upon  any  stated 
diameter  for  the  mandrel. 

For  curving  tests  it  proposes  to  adopt  such  machines  as  will  permit  the  measure- 
ment at  each  instant  of  the  developed  strain  and  the  corresponding  deformation. 

The  Conventions  recommend,  as  has  been  indicated,  the  use  of  slow-moving  ap- 
paratus, acting  either  upon  the  middle  or  at  the  extremity  of  the  test-bar,  but  they 
require  especially  bending  around  a  mandrel  for  the  hot  and  cold  folding  test  of 
irons  and  steels  of  all  kinds,  fixing  upon  a  diameter  of  25  millimeters  for  mandrels 
to  be  adopted  in  the  case  of  wrought  or  cast-iron  for  bridges  and  of  boiler-plates 
more  than  6  millimeters  in  thickness.  The  mandrel  should  not  be  removed  during 
the  test  until  the  ends  of  the  test-pieces  have  become  parallel  to  each  other,  and  the 
bending  will  be  cominued  to  the  point  of  contact  in  the  case  of  test-pieces  of  copper. 

They  add  that  the  test-pieces  employed  should  have  a  rectangular  section,  the> 
width  of  which  should  be  three  times  the  thickness,  and  that  the  edges  should  be 
slightly  rounded. 

They  observe,  besides,  that  the  angle  of  folding  alone  is  not  sufficient  for  judg- 
ing of  the  degree  of  deformation  of  the  test-piece,  but  that  it  is  also  necessary  to 
take  into  account  the  radius  of  external  curvature.  They  propose  to  make  this 
measurement  direct  by  means  of  templets,  or  to  deduce  it  from  the  measure  of  the 
elongation  upon  the  exterior  face. 

They  require,  finally,  that  the  permanent  committee  shall  search  for  the  most 
convenient  method  of  measuring  deformations,  and  they  also  require  that  it  shall 
look  into  folding  tests  made  upon  defective  pieces. 

The  American  Society  also  recommends  the  bending  test  around  a  mandrel,  but 
it  prescribes  the  use  of  mandrels  of  variable  diameters,  and  it  recommends  giving 
them  a  diameter  equal  to  tw7ice  the  thickness  of  the  bar  to  be  tested. 

It  approves,  finally,  the  use  of  a  very  simple  apparatus  which  shall  permit  that 
test  to  be  made  rapidly.  It  fixes  1  inch  (0.025  meter)  as  the  standard  width  to  be 
given  test-pieces  for  folding  tests.  * 

CHAPTER  V.— TORSION  TESTS. 

Our  Commission  confines  itself  to  expressing  the  hope  that  experiments  shall  be 
continued  with  regard  to  the  study  of  torsion. 

The  American  Society  has  given  certain  instructions,  previously  indicated,  with 
regard  to  the  installation  of  apparatus  to  be  used  in  those  tests. 

With  regard  to  test-pieces,  it  recommends  the  use  of  cylindrical  heads,  prohibit- 
ing absolutely  square-shaped  heads.  It  gives  a  sketch  of  the  position  to  be  given 
the  fastenings,  and  it  demands  that  the  distance  between  the  head  and  the  nearest 
point  of  reference  shall  not  be  less  than  one  diameter. 

It  gives  nothing  concerning  the  determination  of  the  useful  or  test  length. 

CHAPTER  VI.— MIXED  TESTS  (SHEARING  AND  PUNCHING). 

Our  Commission  has  expressed  the  wish  that  the  study  of  those  tests  may  be 
continued,  and  it  has  proposed  certain  recommendations  which  may  serve  as  a 
beginning  for  subsequent  regulation. 

The  resolutions  of  the  Conventions  say  nothing  upon  this  subject;  they  recom- 


752  APPENDIX. 

mend  only  that  certain  plates,  like  those  of  wrought  iron  for  boilers,  shall  be  sub- 
mitted to  the  punching  test,  but  they  claim  that  the  test  is  useless  for  plates  of  mild 
steel  or  ingot  iron,  which  should  never  be  punched. 

The  American  Society  remarks  that  in  this  test  special  care  should  be  taken  to 
determine  the  space  to  be  reserved  between  the  edge  of  the  finished  bar  and  the 
edge  of  the  hole  punched  in  the  interior  of  the  section,  in  order  that  cracks  may  not 
be  formed. 

This  question  is  being  studied  by  numerous  experts  both  in  France  and  in  America. 

SECOND    CLASS.— METHODS   OF   TESTING  BY  ABRUPT  ACTION. 

Our  Commission,  in  common  with  the  foreign  resolutions,  indicates  the  particu- 
lar interest  to  be  found  in  shock  tests,  for  they  give  information  which  gradual 
action  cannot  furnish.  It  recommends  that  study  concerning  tensile  tests  by  shock 
and  the  use  of  explosives  may  be  continued. 

CHAPTER  I.— TRANSVERSE  TESTS  BY  SHOCK. 

Our  conclusions  relate  especially  to  tests  on  test-pieces,  as  has  been  shown  above. 
They  fix  the  dimensions  to  be  given  to  test  the  bars,  according  to  the  nature  of  the 
metal  tested,  regulating  under  the  same  conditions  the  weight  of  the  hammer,  the 
form  of  the  striking  face,  and  that  of  the  edges  of  the  supports. 

They  recommend,  besides,  a  continuance  of  theoretical  research,  to  ascertain  the 
respective  effects  of  the  two  elements  which  are  the  component  parts  of  the  energy 
of  shock,  namely,  the  weight  of  the  hammer  and  the  height  of  fall.  They  require 
that  for  each  metal  there  shall  be  determined  the  height  of  fall  above  which  the 
fragility  increases  rapidly,  that  there  shall  be  studied  the  effect  of  constantly  increas- 
ing heights  of  fall  in  ordinary  transverse  tests  made  on  test-pieces  resting  upon  two 
supports,  and  finally  that  there  shall  be  studied  tests  made  by  bringing  the  shock 
to  bear  upon  the  free  end  of  test-pieces  clamped  at  one  end  only. 

Those  different  subjects  are  not  examined  in  the  foreign  resolutions,  which  give 
special  attention  to  tests  upon  whole  pieces,  and  determined,  as  has  been  indicated, 
the  weight  of  the  hammer  and  the  height  of  fall  to  be  used. 

In  tests  upon  finished  pieces  the  resolutions  of  the  Conventions  recommend  the 
use  of  bearing  blocks  or  caps  of  such  form  that  the  upper  surface  of  the  piece  shall 
be  perfectly  horizontal,  the  face  of  the  hammer  being  always  perfectly  smooth  and 
plane.  Those  pieces  should  be  as  light  as  possible. 

Our  Commission  appears  to  think,  however,  that  the  use  of  those  caps  may  be 
dispensed  with  when  it  is  a  question  of  testing  pieces  before  sustaining  in  service 
blows  which  would  be  of  such  a  character  as  to  alter  them. 

In  a  paper  on  shock  tests,  presented  to  the  American  Association  for  the 
Advancement  of  Science  at  its  meeting  of  August,  1894,  in  Brooklyn,  by  Prof.  Mans- 
field Merriman,  vice-president  of  the  society,  the  author  recommends  the  disuse  of 
those  caps;  he  proposes  to  give  the  hammer  a  large  striking  surface  to  avoid  loss 
of  energy  by  heat,  and  to  take  account  of  the  rebound  of  the  hammer. 

The  Conventions  claim,  on  the  other  hand,  that  the  data  derived  from  tests  thus 
far  made  are  not  sufficiently  conclusive  to  admit  of  giving  any  fixed  form  for  either 
the  supports  or  the  pieces  destined  to  receive  the  shock. 

In  observations  on  the  results  they  declare  that  it  is  sufficient  to  determine  the 
curvature  deflection  to  within  about  1  millimeter,  when  it  is  measured  on  a  cord 
of  from  1  to  1.5  meters  in  length. 

In  a  general  way  they  recommend,  as  has  our  Commission,  the  taking  of  careful 
notes  regarding  all  the  peculiarities  of  the  test,  stating,  for  example,  whether  there 
had  been  any  interruption  during  the  test,  whether  the  piece  had  been  turned  over, 
etc. 

CHAPTER  II.— SUPERFICIAL  PENETRATION  TESTS  BY  SHOCK. 

That  mode  of  testing,  minutely  studied  by  our  Commission,  has  not  been 
examined  in  the  foreign  resolutions 


UNIFORM  METHODS  OF  TESTING  METALS.  753 

CHAPTER  III. — PERFORATION  TESTS  BY  SHOCK. 

Our  Commission  has  only  been  able  to  express  a  desire  that  new  experiments 
should  be  made  for  the  purpose  of  solving  the  various  questions  which  have  been 
brought  up  by  that  method  of  test.  The  study  of  that  method  of  test  has  not,  as 
yet,  been  broached  by  the  Conventions  or  by  the  American  Society. 

THIRD    CLASS.— STUDY   OF   HARDNESS   AND    FRAGILITY. 

CHAPTER  I. — PROPOSED  DEFINITIONS  AND  METHODS  OF  MEASURING. 
Our  Commission  has  reserved  the  study  of  that  subject  for  a- future  session. 

CHAPTER  II.— TESTS  OF  HARDNESS  BY  SCRATCHING  AND  BY  RESISTANCE  TO  WEAR 

AND  TEAR. 

Our  Commission  has  expressed  the  hope  that  those  two  subjects  might  be  the 
object  of  complemental  studies. 

The  Conventions  have  expressed  a  like  hope  in  reference  to  the  wear  and  tear  of 
rails  and  tires,  requiring  that  those  tests  shall  be  made  under  conditions  as  nearly 
like  those  of  practice  as  possible. 

The  American  Society  declares  that  it  is  impossible  to  present  any  recommend- 
ations upon  that  subject;  however,  it  points  out  that  for  rails  it  is  proper  to  make 
tests  upon  curved  pieces,  and  to  take  into  consideration  the  action  of  shock,  of 
rapid  rolling,  and  of  variations  in  temperature  and  humidity. 

CHAPTER  III. — FOLDING  TESTS  AFTER  COLD  HARDENING  BY  PUNCHING,  OR  AFTER 

CUTTING. 

The  Conventions  Have  charged  the  permanent  committee  with  searching  for  the 
causes  of  irregularities  in  ingot  iron  shown  by  unexpected  breakages,  notwithstanding 
tests  upon  the  broken  pieces  had  given  satisfactory  results. 

Our  Commission  considers  that  folding  tests  made  after  cold  hardening  (ecrouis- 
sage]  or  cutting  should  show  those  irregularities,  and  it  has  given  in  this  respect 
certain  practical  rules  which  may  in  some  measure  bring  out  the  information  desired 
by  the  Conventions. 

FOURTH  CLASS.— TESTS  OF  MANUFACTURE. 

CHAPTER  I. — COLD-WORKING  TESTS. 

The  enlarging  upon  the  mandrel,  the  heating,  the  flattening,  and  crushing  tests, 
all  studied  in  our  resolutions,  are  not  mentioned  by  the  foreign  resolutions. 

CHAPTER  II.— HOT-WORKING  TESTS  OF  IRONS  AND  STEELS. 

TESTS   BY  BENDING   AND   FOLDING. 

Our  Commission  points  out  certain  tests  to  be  made  on  plates,  angle-iron,  and 
facing-iron ;  for  bars  cut  from  plates  the  same  dimensions  are  assumed  as  for  cold 
folding. 

It  points  out  that  all  these  tests  should  be  made  at  the  same  heat. 

The  Conventions  recommend  that  certain  kinds  of  metals,  such  as  ingot  or 
wrought  iron  for  bridges,  and  plates  of  ingot  iron  or  mild  steel  for  boilers,  shall  be 
subjected  to  the  hot-folding  test.  For  the  latter  a  test  will  also  be  made  after  quench- 
ing The  hot  test  is  made  around  a  mandrel  under  the  same  conditions  as  in  cold 
bending. 


754  APPENDIX. 

TESTS  BY   STAMPING,    BENDING   INTO   HOOKS,    BORING,    PRESSING,    FORGING,   FLATTENING, 

AND   WELDING. 

The  greater  part  of  those  tests  are  not  mentioned  in  the  foreign  resolutions, 
except  those  by  flattening  and  welding. 

The  Conventions  recommend  those  two  modes  of  test  for  different  kinds  of  metals 
without  trying  to  establish  any  definite  rules. 

They  declare  that  it  is  difficult  to  generalize  from  tests  by  welding,  since  much 
depends  upon  the  skilfulness  of  the  operator,  and  they  have  determined  to  require 
a  subcommittee  to  study  the  utility  of  the  various  hot  tests. 

The  American  Society  requires  recourse  to  be  had  to  the  flattening  test  for  testing 
riveted  bars,  and  it  states,  as  does  our  Commission,  that  the  amount  of  spreading 
out  obtained  before  the  appearance  of  fissures  furnishes  one  measure  of  the  quality 
of  the  metal. 

It  insists  strongly  on  the  welding  test,  stating  that  such  a  test  has  a  special 
importance  in  the  United  States,  inasmuch  as  welded  pieces  are  frequently  used 
there. 

It  gives  the  precautions  to  be  observed  in  welding,  which  should  be  done  at  one 
temperature,  a  white  heat,  and  it  requires  that  after  the  operation  the  test-piece 
shall  be  submitted  to  a  tensile  test. 

Another  sample  should  be  submitted  to  a  folding  test  after  a  groove  has  been 
made  of  a  depth  equal  to  that  of  the  weld. 

The  American  Society  demands  that  the  welded  bars  shall  be  allowed  to  cool 
without  being  wet. 

It  does  not  prescribe  the  boring  or  piercing  test  after  welding  recommended  by 
our  Commission. 

FIFTH   CLASS.— SPECIAL  TESTS   ON   CERTAIN   FINISHED   PIECES. 

The  foreign  resolutions  insist  strongly  upon  the  great  interest  that  there  will  be 
in  being  able  to  make  tests  upon  the  finished  pieces  themselves  ;  they  require  that 
in  setting  up  testing-machines  the  possibility  of  making  tests  on  finished  pieces 
shall  be  kept  in  mind.  They  add  that  the  shock  test  is  generally  the  most  important, 
and  for  certain  pieces  in  frequent  use  on  railroads  they  recommend  or  prescribe 
certain  special  tests. 

Our  Commission,  however,  does  not  feel  at  liberty  to  formulate  any  such  resolu- 
tions, and  in  making  its  studies  of  tests  on  finished  pieces  it  confines  itself  to  point- 
ing out  the  method  of  executing  the  tests  without  indicating  that  any  one  may  be 
superior  to  the  others. 

CHAPTER  L— TBBTS  ON  WIRE. 

Our  Commission  has  studied  the  principal  tests  that  may  be  made  on  wire,  i.e., 
tensile,  folding,  winding,  and  torsion. 

The  Conventions  require  upon  this  subject  only  that  the  torsion  test  shall  be 
made  by  means  of  suitable  machines,  and  that  the  folding  test  shall  be  made  by  ma- 
chinery bending  the  piece  alternately  in  two  opposite  directions  around  a  mandrel 
5  millimeters  in  diameter. 

The  American  Society  reproduces  those  conclusions,  requiring,  however,  that  the 
diameter  of  the  mandrel  shall  be  equal  to  that  of  the  wire. 

The  analogous  test  studied  by  our  Commission  is  that  of  winding  or  wrapping. 
It  requires  that  the  diameter  of  the  roller  or  spool  shall  vary  according  to  the 
destined  use  of  the  thread,  but  requires  that  it  shall  be  always  a  multiple  of  the 
diameter  of  the  wire. 

CHAPTER  II.— TESTS  ON  WIRE  ROPE. 

Our  Commission  prescribes  the  rules  to  be  followed  in  tests  for  tension  and  flex- 
ibility. The  Conventions  and  the  American  Society  require  that  a  tensile  and  a 
shock  test  shall  be  made  in  the  longitudinal  direction  without  giving  any  further 
details  on  that  subject.  Our  Commission  expresses  the  hope  that  the  study  of  ten^ 


UNIFORM  METHODS  OF  TESTING  METALS.  755 

sile  tests  by  shock  may  be  continued,  as  well  as  the  folding  or  winding  tests,  in  order 
to  furnish  information  as  to  flexibility. 

The  Conventions  add  that  the  folding  test  is  of  value  only  when  continued  for  a 
given  length  of  time. 

CHAPTER  III.— TESTS  ON  CHAINS. 

Our  Commission  proposes  submitting  chains  to  a  tensile  test  made  at  first  under 
a  moderate  load,  then  carried  to  rupture,  and  it  gives  some  instructions  relating  to 
the  execution  of  that,  test,  For  the  test  under  a  moderate  strain  it  proposes 
adopting  a  strain  double  that  to  be  met  with  in  actual  service. 

The  American  Society  requires  only  that  the  chain  shall  be  subjected  to  the 
service  strain,  and  that  the  elastic  and  permanent  elongation  shall  be  measured  as 
well  as  the  change  in  the  form  of  the  links. 

CHAPTER  IV.— TESTS  ON  RIVETS. 

As  a  special  test  on  bars  for  rivets,  the  American  Society  presents  only  the  hot 
flattening  test. 

Our  Commission  gives  two  principal  tests  :  one  to  separate  the  two  riveted  bands 
or  bars  by  means  of  a  chisel  with  a  given  bevel  driven  by  blows  of  a  hammer,  and 
the  other  to  subject  those  bars  to  a  sort  of  shearing  test. 

CHAPTER  V.— TESTS  ON  PIPES  AND  TUBES. 

The  foreign  resolutions  give  no  special  information  in  regard  to  the  manufacture 
test  to  be  made  on  pipes  or  tubes. 

CHAPTER  VI. — TESTS  BY  HYDRAULIC  PRESSURE. 

For  tests  of  steam-boilers  the  American  Society  recommends  the  adoption  of  the 
method  used  by  the  Hartford  Inspection  Company,  which  is  already  in  general  use 
in  the  United  States. 

•  Our  Commission,  without  prescribing  the  methods  of  test  required  in  France, 
points  out  the  precautions  to  be  observed  and  the  verifications  to  be  made  in  testing 
boilers. 

For  testing  cylinders  and  pipes  the  American  Society  proposes  the  application  of 
a  pressure  equal  to  the  maximum  working  load.  It  requires,  besides,  that  the  dila- 
tion of  pipes  under  that  load  shall  be  observed,  as  well  as  the  permanent  dilation,  if 
any  be  produced,  and  to  mention  whether  the  pipe  leaks. 

In  conclusion,  our  Commission  recalls  the  fact  that  hydraulic  pressure  has  been 
used  recently  to  acquire  desired  data  relating  to  the  elastic  deformation  of  metals  ; 
and  it  expresses  the  hope  that  those  studies  may  be  extended  to  plates. 


APPENDIX  D. 

SPECIFICATIONS   FOR   STRUCTURAL   STEEL. 

I.  PROPOSED  BY  A  COMMITTEE  OF  THE  AMERICAN  SOCIETY  OF 
CIVIL  ENGINEERS,  1896. 

THE  following  specifications  for  structural  rolled  and  for  cast  steel  are  those 
recommended  by  the  Committee  of  the  American  Society  of  Civil  Engineers  (1896)  : 

(  Low  steel  ......  60,000  Ibs.  ±  4,000 

Tensile  strength  \  Medium  steel.  .  65,000    "     ±  4,000 
(  High  steel  .....  70,000    "     ±  4,000 

Yield-point  =  55$  of  the  ultimate  resistance  of  specimen. 

1,500,000 
Per  cent  elonation  m  8  in.  = 


2,800,000 
Per  cent  reduction  of  urea    =  Ultimate- 

Rivet-steel,  when  heated  to  a  low  cherry-red  and  quenched  in  water  at  82°  Fahr., 
must  bend  to  close  contact  without  sign  of  fracture.  Specimens  of  low  steel  when 
treated  and  tested  in  the  same  manner  must  stand  bending  180°  to  a  curve  whose  inner 
radius  is  equal  to  the  thickness  of  the  specimen  without  sign  of  fracture.  Specimens 
of  medium  steel,  as  cut  from  bars  or  plates  and  without  quenching,  must  stand  bend- 
ing 180°  to  an  inner  radius  of  one  and  one  half  times  the  thickness  of  the  specimen 
without  sign  of  fracture  ;  while  those  of  high  steel,  also  without  quenching,  must  stand 
bending  180°  to  a  radius  of  twice  the  thickness  of  the  specimen  without  sign  of 
fracture. 

STEEL  CASTINGS. 

In  steel  castings  the  tension  test  is  recommended,  with  the  following  requirements: 

Ultimate  .................  65,000  Ibs.  per  square  inch. 

Yield-point  ..............  35,000    "      " 

Elongation  in  8  in  ........  =  15$ 

Contraction  ..............  =  25$ 

The  criterion  for  the  elongation  is  that  of  Tetmajer,  which  consists  in  calling 
the  product  of  the  ultimate  strength  by  the  percentage  of  elongation  the  "coeffi- 
cient of  quality."  The  locus  of  this  equation  for  the  elongation,  as  given  above,  is 
shown  in  Fig.  74,  p.  159,  together  with  the  ordinary  limits  of  the  elongation  and  a 
modified  equation  proposed  by  the  author. 

II.  SPECIFICATIONS  PROPOSED  BY  H.  H.  CAMPBELL. 

(In  his  work  "  The  Manufacture  of  Structural  Steel,"  1896.) 

General  Provisions  on  Methods  of  Testing.—  (1)  Rivet-rods  and  other  rounds 
are  to  be  tested  in  the  form  in  which  they  leave  the  rolls,  without  machining. 

Note.  —  This  is  apparently  opposed  to  the  recommendations  of  the  International 

756 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL.  757 

Conferences,*  wherein  it  is  proposed  that  round  test-pieces  shall  be  turned  to  one  of 
four  standard  diameters,  with  shoulders  and  screw-grip  thread  at  each  end,  but  it  is 
stated  elsewhere  in  the  reports  of  the  committee  that  only  pieces  for  scientific  inves- 
tigation are  to  be  prepared  in  this  manner. 

(2)  Test-pieces  from  angles,  plates,  shapes,  etc.,  shall  be  rectangular  in  shape, 
with  a  cross-sectional  area  of  about  one-half  square  inch,  and  shall  be  taken  so  that 
only  two  sides  are  machine-finished,  the  other  two  having  the  surface  which  was  in 
contact  with  the  rolls  in  the  last  pass. 

Note. — The  report  of  the  committee  above  mentioned  recommends  this  method  of 
cutting  tests,  but  specifies  that  there  shall  be  shoulders  at  each  end.  This  necessi- 
tates considerable  extra  machine-work  without  any  notable  effect  upon  the  result. 
The  limitation  of  the  area  of  the  piece  prevents  the  passing  of  inferior  material  by 
an  unusual  increase  in  width. 

(3)  Should  fracture  occur  outside  of  the  middle  third  of  the  gauge  length,  the 
test  is  to  be  discarded  as  worthless  if  it  falls  below  the  standard. 

Note. — This  provision  is  copied  from  the  report  of  the  above  committee,  and  is 
much  to  be  commended.  A  deficient  elongation  when  the  piece  breaks  near  tlte 
end  is  not  the  fault  of  the  material,  but  a  mere  accident.  On  eye-bars,  a  failure  in 
the  eye  should  condemn  the  method  of  forming  the  head  rather  than  the  quality  of 
the  steel. 

(4)  In  case  one  test-piece  falls  slightly  below  the  requirements  in  any  particular, 
the  inspector  shall  allow  the  retesting  of  the  lot  or  heat  by  taking  four  additional 
tests  from  the  same  lot  or  heat,  and  if  the  average  of  the  five  shall  show  that  the 
steel  is  within  the  requirements,  the  metal  shall  be  accepted. 

(5)  Drillings  for  chemical  analysis  may  be  taken  either  from  the  preliminary 
test-piece  or  from  the  finished  material  ;  but  if  the  sample  be  taken  from  the  centre 
of  a  sheared  or  universal-mill  plate,  the  maximum  limit  of  both  phosphorus  and 
sulphur  shall  be  raised  25  per  cent;  e.g.,  from  .04  to  .05  per  cent,  or  .08  to  .10  per 
cent. 

(6)  The  pulling  speed  of  the  machine  for  breaking  test-pieces  shall  not  be  less 
than  one-quarter  inch  per  minute  nor  more  than  three  inches  per  minute. 

(7)  The  elastic  limit  shall  be  determined  by  the  dropping  of  the  beam. 
Classes  of  Steel  Proposed. — The  following  specifications  do  not  deal  with  metal 

for  special  purposes,  like  gun-carriages,  armor-plate,  etc.,  but  are  intended  to  cover 
more  or  less  fully  the  needs  of  the  structural  engineer.  I  do  not  expect  that  they 
will  ever  be  adopted  in  their  entirety  as  standard  requirements,  but  this  seems  to 
be  the  simplest  form  in  which  to  condense  the  investigations  that  have  been  recorded 
in  the  foregoing  chapters,  and  to  present  the  variations  in  the  physical  properties- 
caused  by  changes  in  the  history  and  section  of  the  test-piece. 

Engineers  who  do  not  wish  to  cumber  their  specifications  with  so  many  allow- 
ances for  thickness  and  section  will  find  herein  the  reason  for  many  troublesome 
questions  arising  in  the  testing  of  the  material,  for  I  have  tried  to  tabulate,  as  fairly 
as  can  be  estimated,  the  effect  of  conditions  that  are  ruled  more  by  the  laws  of  nature 
than  by  the  skill  of  the  manufacturer. 

At  the  same  time  it  will  be  found  that  the  matter  is  not  as  complicated  as 
would  be  indicated  at  first  sight,  for  one  page  of  general  provisions  and  one  page  of 
physical  limits  for  each  kind  of  steel  can  hardly  be  called  a  very  voluminous  docu- 
ment to  cover  the  specifications  upon  structural  shapes. 

The  engineer  who  will  compare  the  proposed  requirements  with  what  is  demanded 
in  other  countries  will  find  a  remarkable  difference.  The  specifications  which  are 
in  general  use  in  Germany  are  as  follows  t: 

For  Rivets. — Ultimate  strength  from  51,200  to  59,700  pounds  per  square  inch; 
elongation  22  per  cent  in  eight  inches. 

For  Other  Structural  Material. — Lengthwise  tests  :  Ultimate  strength  from 
52,600  to  62,600  pounds  per  square  inch  ;  elongation  20  per  cent  in  eight  inches. 

Crosswise  tests  :  Ultimate  strength  from  51,200  to  64.000  pounds  per  square 
inch  ;  elongation  17  per  cent  in  eight  inches. 

*  Report  of  Committee  on  Standard  Tests  to  the  Am.  Soc.  Meek.  Eng.,  Appendix  V. 
t  Normalbedingungen  fur  die  Lieferung  von  Eisenconstruktionen  fur  Briicken-  und  Hochbau 
(Otto  Meissner,  1893);  also,  Ueber  die  Arbeiten  der  Flusseisen-Commission  (F.  Kintzle,  1892). 


758 


APPENDIX. 


These  are  given  as  the  limits  accepted  by  the  leading  engineering  societies  of  that 
country,  and  I  am  informed  by  Mr.  Kintzle*  that  they  represent  the  general  re- 
quirements at  the  present  time  for  all  classes  of  material.  It  is  safe  to  say  that  if 
American  engineers  were  satisfied  with  the  German  standards,  there  would  not  be 
one  rejection  for  deficient  ductility  where  there  are  twenty  under  our  more  rigid 
requirements  ;  and  if  they  would  be  content  with  a  steel  having  an  ultimate 
strength  between  52,000  and  62,000  pounds  per  square  inch,  there  would  not  be 
one  fifth  the  number  of  heats  discarded  for  being  outside  of  the  tensile  limits.  The 
bearing  of  these  facts  upon  the  cost  of  the  material  is  self-evident. 

I  do  not  advocate  any  sacrifice  of  strength  to  economy,  but  I  would  impress  upon 
American  engineers  that  this  soft  metal  is  eminently  suitable  for  structural  work, 
while  by  maintaining  their  present  chemical  limitations  and  their  requirements  con- 
cerning ductility  they  will  be  assured  of  a  material  which  is  equal  in  quality  to  any 
produced  in  the  world. 

CLASS  I. — EXTRA  DEAD  SOFT;  FOR  COMMON  RIVETS,  WIRE  CABLES,  AND  OTHER 
PURPOSES    WHERE    EXCEPTIONAL   TOUGHNESS    IS    REQUIRED. 


Method  of  manufacture:  Basic  open-hearth  process. 
Chemical  composition,  in  per  cent:  P  below  .04;  S  below  .( 
Physical  requirements  as  follows: 


!;  Si  below  .01;  MM  below  .50. 


Ultimate  Strength, 

Shape. 

Diameter  in 
Inches. 

Pounds  per  Square  Inch. 

Elastic  Ratio. 

Elongation 
in  8  Inches, 
Per  Cent. 

Reduction 
of  Area, 
Per  Cent. 

Minimum. 

Maximum. 

Rivet-rods 

% 

46000 

55000 

64.0 

28.0 

52 

H 

46000 

54000 

63.0 

29.0 

58 

% 

45000 

54000 

61.5 

29.25 

56 

1 

45000 

54000 

60.0 

29.50 

54 

1^ 

44000 

54000 

58.5 

29.75 

52 

1% 

44000 

54000 

57.0 

30.00 

50 

A  rolled  round  about  three-quarters  inch  in  diameter,  after  being  nicked  about 
one-quarter  way  through,  shall  bend  completely  double  without  fracture,  with  the 
nick  on  the  outer  curve  of  the  bend. 

Heats  rolled  into  bars  less  than  five-eighths  inch  in  diameter  may  be  tested  in 
trial  rods  of  three-quarters  inch. 

If  any  bar  fails  to  pass  the  physical  tests,  four  more  pieces  shall  be  taken  from 
the  same  heat,  and  the  average  of  all  five  bars  shall  be  considered  the  true  record. 

Kivets,  when  cut  out  of  the  work  into  which  they  have  been  put,  shall  show  a 
tough  silky  structure,  with  no  crystalline  appearance. 

/See  also  general  provisions,  p.  756. 

CLASS  II. — BRIDGE    RIVETS;    FOR    RIVETS    IN    RAILROAD    BRIDGES. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:  P  below  .04  in  acid  steel,  below  .03  in  basic;  S  below  .05;  Si 
below  .04;  Mn  below  .50. 

Physical  requirements  as  follows: 


Shape. 

Diameter 
in  Inches. 

Ultimate  Strength. 
Lbs.  per  Square  Inch. 

Elastic 
Ratio. 

Elongation  in  8  Inches, 
Per  Cent. 

Average 
Reduction 
of  Area, 
Per  Cent. 

Minimum. 

Maximum. 

Average. 

Minimum. 

Rivet-rods. 

1 

iH 
m 

48000 
48000 
47000 
47000 
40000 
46000 

57000 
56000 
56000 
56000 
56000 
56000 

66.0 
•     65.0 
63.5 
62.0 
60.5 
59  0 

29.0 
30.0 
30.5 
31.0 
31.0 
31  0 

27.0 
28.0 
28.5 
29.0 
29.0 
29.0 

60 
60 
58 
56 
54 
52 

*  Private  communication,  February,  1896. 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL. 


759 


Two  tons  of  bars  from  the  same  heat  shall  constitute  a  lot,  and  two  specimens, 
each  from  a  different  bar,  shall  be  tested  from  each  lot.  The  above  table  gives  the 
average  required  of  these  two  bars,  and  the  minimum  below  which  no  bar  shall  fall. 
If  the  average  elongation  or  reduction  of  area  on  any  one  lot  shall  fall  below  the 
requirement,  two  additional  bars  shall  be  cut  from  the  same  lot,  and  the  average 
of  the  four  pieces  shall  be  considered  the  average  of  the  lot,  provided  that  no  con- 
cession be  made  in  the  minimum.  Heats  rolled  into  sizes  less  than  five-eighths 
inch  may  be  tested  in  trial  rods  of  three-quarters  inch. 

A  rolled  round  about  three-quarters  inch  in  diameter,  after  being  nicked  one- 
quarter  way  through,  shall  bend  completely  double  without  fracture,  with  the  nick 
on  the  outer  curve  of  the  bend.  A  piece  of  three-quarter-inch  rod  cut  one-half  inch 
long  shall  be  upset  while  cold  into  a  disk  one-eighth  inch  thick,  without  developing 
extensive  flaws  or  showing  signs  of  cold-shortness. 

Rivets,  when  cut  out  of  the  work  into  which  they  have  been  put,  shall  show  a 
tough  silky  structure,  with  no  crystalline  appearance. 

See  also  general  provisions,  p.  756. 


CLASS   III.— HARD   BRIDGE    RIVETS;    A    SUBSTITUTE    FOR   CLASS   II,    GIVING 
GREATER   STRENGTH   WITH    LESS   TOUGHNESS. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:  P  below  .04  in  acid  steel,  below  .03  in  basic;  S  below  .05;  Si 
below  .04;  Mn  below  .60. 

Physical  requirements  as  follows: 


Shape 

Diameter 

Ultimate  Strength. 
Lbs.  per  Square  Inch. 

Elastic 

Elongation  in  8  Inches, 
Per  Cent. 

Average 
Reduction 

Minimum. 

Maximum. 

Average. 

Minimum. 

Per  Cent. 

Rivet-rods. 

% 

54000 

63000 

61  0 

28.0 

26.0 

55 

&i 

54000 

62000 

60.0 

29.0 

27.5 

55 

% 

53000 

62000 

58.5 

29.5 

27.5 

53 

1 

53000 

62000 

57.0 

30.0 

28.0 

51 

1J-6 

52000 

62000 

55.5 

30.0 

28.0 

49 

& 

52000 

62000 

54.0 

30.0 

28.0 

47 

Two  tons  of  bars  from  the  same  heat  shall  constitute  a  lot,  and  two  specimens, 
each  from  a  different  bar,  shall  be  tested  from  eacli  lot.  The  above  table  gives  the 
average  required  of  these  two  bars,  and  the  minimum  below  which  no  bar  shall 
fall.  If  the  average  elongation  or  reduction  of  area  on  any  one  lot  shall  fall  below 
the  requirement,  two  additional  bars  shall  be  cut  from  the  same  lot?  and  the  aver- 
age of  the  four  pieces  shall  be  considered  the  average  of  the  lot,  provided  that  no 
concession  be  made  in  the  minimum.  Heats  rolled  into  sizes  less  than  five-eighths 
inch  may  be  tested  in  trial  rods  of  three-quarters  inch. 

Rivets,  when  cut  out  of  the  work  into  which  they  have  been  put,  shall  show  a 
tough  silky  structure,  with  no  crystalline  appearance. 

See  also  general  provisions  p.  756. 


760 


APPENDIX. 


CLASS    IV.— COMMON    HARD    RIVETS;    FOR    ROOF-TRUSSES    AND     OTHER 
STRUCTURES   NOT   EXPOSED   TO   SHOCK. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:  P  below  .06  in  acid  steel,  below  .04  in  basic;  S  below  .05;  Si 
below  .04;  Mn  below  .60. 

Physical  requirements  as  follows: 


Ultimate  Strength, 

Shape. 

Diameter  in 
Inches. 

Pounds  per  Square  Inch. 

Elastic  Ratio. 

Elongation 
in  8  Inches, 
Per  Cent. 

Reduction 
of  Area, 
Per  Cent. 

Minimum. 

Maximum. 

Rivet-rods. 

% 

54000 

63000 

61  0 

27.0 

55 

54000 

62000 

60.0 

28.0 

55 

" 

% 

53000 

62000 

58.5 

28.5 

53 

u 

1 

53000 

62000 

57.0 

29.0 

51 

K 

1^ 

52000 

62000 

55.5 

29.0 

49 

" 

1J4 

52000 

62000 

54.0 

29.0 

47 

Four  tests  shall  be  taken  from  each  heat,  and  the  average  of  these  four  shall 
conform  to  the  above  table.  If  the  average  elongation  or  reduction  of  area  of  any 
heat  shall  fall  below  the  requirement,  four  additional  bars  may  be  cut  from  the 
same  heat,  and  the  average  of  the  eight  pieces  shall  be  considered  the  average  of  the 
heat.  Heats  rolled  into  sizes  less  than  five-eighths  inch  may  be  tested  in  trial  rods 
of  three-quarters  inch. 

Rivets,  when  cut  out  of  the  work  into  which  they  have  been  put,  shall  show  a 
tough  silky  structure,  with  no  crystalline  appearance. 

See  also  general  provisions,  p.  756. 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL. 


761 


CLASS  V. — SOFT  BRIDGE  STEEL;  FOR  ANGLES,  PLATES,  BARS,  ETC.,  FOR  BRIDGES, 
CRANES,    AND    SIMILAR    STRUCTURES    EXPOSED    TO    SHOCK. 

Method  of  manufacture,  in  per  cent:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:  P  below  .06  in  acid  steel,  below  .04  in  basic;  S  below  .07  in 
plates  and  angles,  below  .06  in  eye-bars;  Si  below  .04;  Mn  below  .50. 
Physical  requirements  as  follows: 


1 
1 

1 

c 

cc 

OS 

OJ 
C 

EH 

Ultimate 
Strength, 
I.bs.  per 
Sq.  In. 

Elastic  Ratio. 

1  Elongation  in  8  Inches, 
Per  Cent. 

1  Reduction  of  Area, 
Per  Cent. 

Remarks. 

Minimum. 

Maximum. 

i 

"tab 
c 

1 

50000 
50000 
49000 
49000 
48000 

58000 
58000 
58000 
58000 
58000 

63.0 
61.5 
60.0 
58.5 
57.0 

29.0 
29  0 
29.0 
29.0 
29.0 

55 
53 
51 
49 
47 

One  piece  of  %-inch  angle  must  open  out  flat  and  another 
close  shut  without  sign  of  fracture. 

Eye-bars,  1  PlofAo 
annealed.  |  Plates. 

5/16 

53000 
51000 
50000 
49000 

48000 
47000 

63000 
61000 
60000 
59000 
58000 
58000 

65.0 
63.0 
6-2.0 
60.0 
58.0 
56.0 

23.0 
26.0 
26.0 
25.0 
24.0 
23.0 

44 
50 
50 
48 
46 
44 

On  plates  under  42  inches  wide  the  required  elongation 
shall  be  raised  1.5  per  cent,  and  the  reduction  of  area  2.0  per 
cent.  On  plates  over  70  inches  wide  the  elongation  shall  be 
lowered  1.5  per  cent,  and  the  reduction  of  area  2.0  per  cent, 
On  tests  cut  crosswise  from  the  sheet,  the  minimum  tensile 
strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  percent, 
and  the  reduction  of  area  10  per  cent.  On  universal  niill- 
plates  the  allowance  for  transverse  tests  shall  be  5000  Ibs., 
5  per  cent  and  15  per  cent.  Both  longitudinal  and  trans- 
verse strips  cut  from  plates  shall  bend  double  flat.  When 
every  plate  in  the  heat  is  tested,  the  minimum  elongation 
and  reduction  shall  be  lowered  5  per  cent. 

2  3 

50000 
50000 
49000 
49000 
48000 

58000 
58000 
58000 
58000 
58000 

57  0 

The  elongation  in  full  length  shall  be  15  per  cent  in  bars 
from  10  to  20  ft.  long,  14  per  cent  in  21  to  25  ft.,  13.5  per  cent 
in  26  to  30  ft.,  and  13  percent  in  31  to  35  ft. 

56.0 
54.0 
53.0 

52.0 

SHAPES.— In  channels,  beams,  etc.,  the  requirements  on  tests  cut  from  the  web  shall  be  the  same 
as  for  plates  between  42  and  70  inches  wide,  with  the  same  allowance  for  difference  in  thickness.  In 
tests  cut  from  the  flange  the  minimum  tensile  strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  per 
cent,  and  the  reduction  of  area  10  per  cent. 


See  also  general  provisions,  p.  756. 


762 


APPENDIX. 


CLASS    VI. — MEDIUM    BRIDGE    STEEL;     A    SUBSTITUTE   FOE   CLASS    V   WHEN 
GREATER   STRENGTH   AND    LESS   TOUGHNESS   ARE   REQUIRED. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  iu  per  cent:  P  below  .06  in  acid  steel,  below  .04  in  basic;  S  below  .07  in 
plates  aud  angles,  below  .06  in  eye-bars;  Si  below  .04;  Mn  below. .60. 
Physical  requirements  as  follows: 


Ultii 

nate 

X 

§5 

Strei 

igth, 

0 

sf 

o 

Lbs 

per 

^ 

C 

Sq. 

In. 

GO 

«1 

6 

CM 

+a 

C    •!-=' 

Remarks. 

i 

g 

I 

& 

•II 

S) 

5 

E 

.2 

*p 

o"^ 

1 

1 

03 

cS 

5  ^ 

11 

a 

H 

S 

H 

a 

M 

% 

56000 

64000 

63.0 

27.0 

50 

1 

1 

56000 
55000 
55000 

64000 
64000 
64000 

61.5 
60.0 
58.5 

27.0 
27.0 
27.0 

48 
46 
44 

One  piece  of  angle,  not  over  y%  inch  thick,  shall  open  out 
flat,  and  another  close  shut  without  sign  of  fracture. 

< 

54000 

64000 

57.0 

27.0 

42 

On  plates  under  42  inches  wide  the  required  elongation 
shall  be  raised  1.5  percent,  and  the  reduction  of  area  2.0  per 

cent.  On  plates  over  70  inches  wide.the  elongation  shall  be 

1 

5/16 

59000 
57000 
50000 
55000 
54000 
53000 

69000 
67000 
6(3000 
65000 
64000 
64000 

62.0 
60.0 
59.0 
57.0 
55  0 
53.0 

22.0 
25.0 
25.0 
24  0 
23.  C 
22.0 

39 
45 
45 
43 
41 
39 

lowered  1.5  per  cent,  and  the  reduction  of  area  2.0  per  cent. 
On  tests  cut  crosswise  from  the  sheet  the  minimum  tensile 
strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  percent, 
and  the  reduction  of  area  10  per  cent.  On  universal  mill- 
plates  the  allowance  for  transverse  tests  shall  be  5000  Ibs., 
5  per  cent  and  15  per  cent.  Longitudinal  strips  shall  bend 
double  flat;  transverse  strips  shall  bend  through  180  degrees 
around  a  pin  1  inch  in  diameter.  When  every  plate  in  the 

heat  is  tested,  the  minimum  elongation  and  reduction  of 

area  shall  be  lowered  5  per  cent. 

03-' 

Q/ 

56000 

64000 

56  0 

1 

56000 

64000 

55.0 

The  elongation  in  full  length  shall  be  14  per  cent  in  bars 

11 

2^ 

55000 
55000 

64000 
64000 

53.0 
52.0 

from  10  to  20  ft.  long,  13  per  cent  in  21  to  25  ft.,  12.5  per  cent 
in  26  to  30  ft.,  and  12  per  cent  in  31  to  35  ft. 

K'S 

2H 

54000 

64000 

51.0 

SHAPES. — In  channels,  beams,  etc.,  the  requirements  on  tests  cut  from  the  web  shall  be  the  same 
as  for  plates  between  42  and  70  inches  wide,  with  the  sa-me  allowance  in  thickness.  In  tests  cut  from 
the  flange,  the  minimum  tensile  strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  percent,  and  the 
reduction  of  area  10  per  cent. 

NOTE.— The  allowable  content  of  phosphorus  may  be  raised  to  .08  per  cent  for  acid  and  .05  per 
cent  for  basic  steel,  if  the  best  quality  is  not  required,  but  other  specifications  must  remain  the 
the  same. 


See  also  general  provisions,  p.  756. 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL. 


763 


CLASS    VII.— HARD    BRIDGE    STEEL. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:   P  below  .06  in  acid  steel,  below  .04  in  basic;  S  below   07  in 
plates  and  angles,  below  .06  in  eye-bars;  Si  below  .05;  Mn  below  .80. 
Physical  requirements  as  follows; 


. 

Ultimate 

0) 

« 

Strength, 

o 

cf 

Lbs.  per 

h-  1 

1 

Sq.  In. 

oc 

<l 

o 

c 

q_^ 

^ 

c  a' 

Remarks. 

a 

5 

3 

C 

M 

"So 

|1 

D 

2 

•£2 

b£  u 

5* 

u 

a 

| 

3 

ll 

-5^ 

CQ 

EH 

i 

£2 

W 

W 

« 

% 

60000 

68000 

62.0 

26.0 

48 

CD 

1Z 

60000 

68000 

60  5 

26  0 

46 

H 
p 

•34 

59000 
58000 

68000 
68000 

59.0 
57.5 

26.0 
26.0 

44 
42 

One  piece  of  angle,  less  than  y»  inch  thick,  shall  open  out 
flat,  and  another  piece  close  shut  without  sign  of  fiacture. 

% 

57000 

68000 

56.0 

26.0 

40 

On  plates  under  42  inches  wide  the  required  elongation 
shall  be  raised  1.5  per  cent,  and  the  reduction  of  area  2.0  per 

cent.  On  plates  over  70  inches  wide,  the  elongation  shall  be 

Plates. 

1 

63000 
61000 
60000 
59000 
58000 
57000 

73000 
71000 
70000 
69000 
68000 
68000 

60.0 
58.0 
57.0 
55.0 
P-3.0 
51.0 

20.0 
23.0 
23.0 
2-^.0 
21.0 
20.0 

34 
40 
40 
38 
36 
34 

lowered  1.5  per  cent,  and  the  reduction  of  area  2.0  per  cent. 
On  tests  cut  crosswise  from  the  sheet  the  minimum  tensile 
strength  shall  be  lowered  3000  Ibs..  the  elongation  3  per  cent, 
and  the  reduction  of  area  10  per  cent.  On  universal  mill- 
plates  the  allowance  for  transverse  tests  shall  be  5000  Ibs  , 
5  per  cent  and  15  per  cent.  Longitudinal  strips  shall  bend 
double  flat.  Transverse  strips  shall  bend  through  180  degrees 

around  a  pin  1  inch  in  diameter.  When  ever}-  plate  in 

the  heat  is  to  be  tested,  the  minimum  elongation  and  reduc- 
tion of  area  shall  be  lowered  5  per  cent. 

of—  ' 

§4 

60000 

68000 

55.0 

3.2 

1 

60000 

68000    54.0 

The  elongation  in  full  length  shall  be  13  per  cent  in  bars 

J* 

59000 
59000 

68000    52.0 
68000'  51.0 

from  10  to  20  ft.  long,  12.5  per  cent  in  21  to  25  ft.,  12  per  cent 
in  26  to  30  ft.,  and  11  .5  per  cent  in  31  to  35  ft 

w  5 

w 

58000 

68000    50.0 



SHAPES.— In  channels,  beams,  etc.,  the  requirements  on  tests  cut  from  the  web  shall  be  the  same 
as  for  plates  between  42  and  70  inches  wide,  with  the  same  allowance  for  difference  in  thickness.  In 
tests  cut  from  the  flange  the  minimum  tensile  strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  per 
cent,  and  the  reduction  of  area  10  per  cent. 

NOTE.— The  allowable  content  of  phosphorus  may  be  raised  to  .08  per  cent  *n  acid  and  .05  per 
cent  in  basic  steel,  if  the  best  quality  is  not  required,  but  other  specifications  must  remain  the 
same. 


See  also  general  provisions,  p.  756. 


764 


APPENDIX. 


CLASS  VIII. — EXTRA  HARD  BRIDGE  STEEL;  FOR  SPECIAL  STRUCTURES  WHERE 
GREAT    STIFFNESS    IS    ESSENTIAL. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  hi  per  cent:  P  below  .06  in  acid  steel,  below  .04  in  basic;  S  below  .07  in 
plates  and  angles,  below  .06  in  eye-bars;  Si  below  .10;  Mu  below  .80. 
Physical  requirements  as  follows: 


^   |    Ultimate 

c/: 

3; 

o> 

Strength, 

"o 

=f 

V 

Lbs.  per 
Sq.  In. 

GO 

£ 

•S 

!J5 

C  -^> 

O     . 

Remarks. 

cc 

c 

g 

Ctf 

K 

•2g 

C  ^ 

o  5 

s, 

D 
J5 

a 

a 

S 

.g 

1" 

ci 

,2 

'3 

"i 

1 

O  ij 

'O  ^ 

a 

H 

i 

« 

3 

s 

« 

a/ 

64000 

72000 

61.0 

25.0 

45 

I 

I 

64000 
63000 
62000 

72000 
72000 
72000 

59.5 
58.0 
56.5 

25.0 
25.0 
25.0 

43 
41 
39 

One  piece  of  angle,  about  %-inch  thick,  shall  open  out 
flat,  and  another  piece  close  shut  without  sign  of  fracture. 

% 

61000 

72000 

55.0 

25.0 

37 

On  plates  under  42  inches  wide  the  required  elongation 

shall  be  raised  1.5per  cent,  and  the  reduction  of  area  2.0  per 

cent.     On  plates  over  70  inches  wide  the  elongation  shall  be 

5/16 

67000 
65000 

77000 
75000 

59.0 
57.0 

18.0 
21.0 

32 

38 

lowered  1.5  per  cent,  and  the  reduction  of  area  2.0  per  cent. 
On  tests  cut  crosswise  from  the  sheet  the  minimum  tensile 

CS 

1 

64000 
63000 

74000 
73000 

56.0 
54.0 

21.0 
20.0 

38 
36 

strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  per  cent, 
and  the  reduction  of  area  10  percent.     On  universal  mill- 

£•4 

1 

62000 

72000 

52.0 

19  0 

34 

plates  the  allowance  for  transverse  tests  shall  be  5000  Ibs  , 

1^ 

61000 

72000 

50.0 

18.0 

32 

5  per  cent  and  15  per  cent.    Longitudinal  strips  shall  bend 
double  flat.     When  every  plate  in  the  heat  is  to  be  tested, 

the  minimum  elongation  and  reduction  of  area    shall  be 

lowered  5  per  cent. 

"^5 

% 

64000 

7-JOOO 

54.0 



l| 

1 

64000 
63000 

72000 
72000 

53.0 
51.0 

The  elongation  in  full  length  shall  be  12.5  percent  in  bars 
from  10  to  20  ft.  long,  12.0  per  cent  in  21  to  25  ft.,  11.5  per 

>,5 

2  2 

63000 

72000    50.0 

cent  in  26  to  30  ft.,  and  11.0  per  cent  in  31  to  35  ft. 

w  S 

2Y* 

62000 

72000 

49.0 

SHAPES. — In  channels,  beams,  etc.,  the  requirements  on  tests  cut  from  the  web  shall  be  the  same 
as  for  plates  between  42  and  70  inches  wide,  with  the  same  allowances  for  difference  in  thickness.  In 
tests  cut  from  the  flange  the  minimum  tensile  strength  shall  be  lowered  3000  Ibs.,  the  elongation  3  per 
cent,  and  the  reduction  of  area  10  per  cent. 

NOTE. — The  allowable  content  of  phosphorus  may  be  raised  to  .08  per  cent  for  acid  steel  and 
.05  per  cent  for  basic,  if  the  best  quality  is  not  required,  but  other  specifications  must  remain  the 
same. 


/See  also  general  provisions,  p.  756. 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL. 


765 


CLASS  IX.— FORGING  STEEL;    FOR  PINS  AND  MISCELLANEOUS  FORCINGS  AND 
FOR    SPECIAL    PLATES    AND    ANGLES. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:  P  below  .06  in  acid  steel,  below  .04  in  basic;  S  below  .07  in 
plates  and  angles,  below  .06  in  eye-bars;  Si  below  .10;  Mn  below  .90. 
Physical  requirements  as  follows: 


Ultimate 

1 

V 

Strength, 

a 

cf 

•^ 

Lbs.  per 

fl 

£ 

Sq.  In. 

6 

oo 

a 

*j 

. 

•» 

c  *^' 

°  _,_; 

Remarks. 

w 

£ 

a 

23 

.2  = 

c  5 

aJ 
P. 

,3 

.0 

3 

'5 

| 

'x 

i 

CO 

§1 

03 

H 

s 

s 

K    ' 

H 

H 

% 

70000    80000 

58.0 

22.0 

42 

1 

'- 

% 

70UOO    80000    56.5 
69000  i  80000  i  55.0 
68000'  HOOOO'  53.5 

22.0 
22.0 
22.0 

40 
38 
36 

One  piece  of  angle  %-inch  thick,  shall  open  out  flat,  and 
another  piece  close  shut  without  sign  of  fracture. 

s 

67000    80000    52.0 

22.0 

34 

On  plates  under  42  inches  wide  the  required  elongation 

5/16 

73000    83000    56.0 
71000    81000.  54.0 

16.0 
19.0 

30 
36 

shall  be  raised  1.5  percent,  and  the  reduction  of  area  2.0  per 
cent.     On  plates  over  70  inches  wide,  the  elongation  shall  be 

1 

H 

70000    80000  i  53.0 
69000    79000  i  51.0 

19.0 
18.0 

36 
34 

lowered  1.5  per  cent,  and  the  reduction  of  area  2.0  per  cent. 
Longitudinal  strips  under  y^  inch   thick  shall  bend  double 

P^ 

1 

68000    78000 

49.0 

17.0 

32 

flat.     AMien    every  plate  in   the  heat  is  to   be  tested,  the 

1/4 

67000:  78000 

47.0 

16.0 

30 

minimum  elongation  and  reduction  of  area  shall  be  low- 

ered 5  per  cent. 

When  this  steel  is  used  for  pins  or  forgings,  a  charge  may  be  tested  by  rolling  a 
small  test  ingot  or  piece  of  bloom  into  a  bar  with  a  cross-section  of  about  0.5  or  1.0 
square  inch.  This  bar  should  have  an  ultimate  strength  of  between  70,000  and 
80,000  pounds  per  square  inch,  an  elastic  ratio  of  58  per  cent,  and  an  elongation  of 
15  per  cent  in  eight  inches.  This  method  will  usually  suffice  to  show  the  quality  of 
the  steel.  If  it  is  desirable  to  test  the  forged  work,  a  bar  should  be  cut  from  a  rolled 
or  hammered  piece  about  six  inches  in  smallest  dimension,  and  turned  to  a  three- 
quarter-inch  round,  two  inches  between  shoulders.  This  should  have  an  ultimate 
strength  of  between  67,000  and  80,000  pounds  per  square  inch,  an  elastic  ratio  of  50 
per  cent,  and  elongation  of  20  per  cent  in  two  inches.  The  test-piece  should  be 
cut  at  a  depth  of  about  two  inches  from  the  outside. 

See  also  general  provisions,  p.  756. 


766 


APPENDIX. 


CLASS   X. — HARD   FORGING   STEEL;    FOR   MISCELLANEOUS   FORCINGS. 

Method  of  manufacture:  Acid  or  basic  open-hearth  process. 

Chemical  composition,  in  per  cent:  P  below  .05  in  acid  steel,  below  .03  in  basic;  S  below  .07;   S 
below  .10;  Mn  below  .90. 

Physical  requirements  as  follows: 


Shape  and  Origin  of  Test-piece. 

Ultimate 
Strength, 
Pounds  pel- 
Square  Inch. 

_o 

55 
45 

Elongation,  Per  Cent. 

S 

I 

"c 

75000 
75000 

Maximum. 

A  i 
Aj 

•oiled  bar  with  a  cross-section  of  about  0.5  to  1.0  square  inch,  made 
from  a  bloom  or  test  ingot.     Elongation  measured  in  8  inches  
4-inch  round,  2  inches  long  between  shoulders,  cut  from  a  rolled  or 
forged  piece  about  G  inches  in  smallest  dimension.     Elongation  meas- 
ured in  2  inches.   .     

100000 
100000 

12 

15 

The  first  method  will  suffice  for  ordinary  work  to  show  the  quality  of  the 
material.  The  second  involves  considerable  expense  and  delay  in  cutting  and  finish- 
ing the  piece,  and  there  is  necessarily  much  variation  caused  by  the  different  sizes 
and  shapes  of  forgings.  The  test-piece  should  be  cut  at  a  depth  of  about  two  inches 
from  the  outside. 

See  also  general  proms  ions,  p.  756. 

CLASSES  XI,  XII,  AND  XIII.— For  buildings,  highway  bridges,  and  other  struc- 
tures not  exposed  to  shock. 

The  requirements  on  material  for  ordinary  structures  need  not  be  so  carefully 
drawn  as  in  the  case  of  railroad  bridges.  Hence  it  will  suffice  to  accept  the  standard 
specifications  of  the  Association' of  American  Steel  Manufacturers  given  on  the 
following  pages.  They  are  here  given  in  full,  since  the  clauses  relating  to  the 
inspection  of  material,  and  the  allowance  for  overweights,  apply  equally  to  all 
classes  of  material.  The  Association  did  not  limit  the  use  of  this  metal  to  buildings 
not  exposed  to  shock,  for  the  matter  of  chemical  composition  was  left  open  to  the 
engineer,  but,  in  common  with  almost  all  manufacturers,  I  must  unqualifiedly  con- 
demn the  use  of  metal  for  a  railway  bridge  that  contains  over  .08  per  cent  of 
phosphorus,  while  I  believe  that  .06  per  cent  should  be  the  upper  limit. 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL.  767 


III.— STANDARD  SPECIFICATIONS  GOVERNING  THE  CHEMICAL  AND 
PHYSICAL  PROPERTIES  OF  STRUCTURAL  AND  SPECIAL  OPEN- 
HEARTH  PLATE  AND  RIVET  STEEL,  AS  ADOPTED  BY  THE  ASSOCIA- 
TION OF  AMERICAN  STEEL  MANUFACTURERS*  ON  AUGUST  9TH, 
1895,  REVISED  JULY  17TH,  1896, 

AND  SINCE  FORMALLY  APPROVED  BY  THE  FOLLOWING  COMPANIES  :  THE  BETHLEHEM 
IRON  CO.;  CAMBRIA  IRON  CO.;  CARBON  STEEL  CO.;  THE  CARNEGIE  STEEL  CO.,  LIMITED; 
CATASAUQUA  MANUFACTURING  CO.;  CENTRAL  IRON  WORKS;  CLEVELAND  ROLLING  MILL 
CO.;  COLORADO  FUEL  AND  IRON  CO.;  GLASGOW  IRON  CO.;  ILLINOIS  STEEL  CO.;  JONES  & 
LAUGHLINS,  LIMITED;  LUKENS  IRON  AND  STEEL  CO.;  OTIS  STEEL  CO.,  LIMITED;  PACIFIC 
ROLLING  MILL  CO.  ;  PASSAIC  ROLLING  MILL  CO. ;  PAXTON  ROLLING  MILLS;  PENNSYLVANIA 
STEEL  CO.;  POTTSTOAVN  IRON  CO.;  POTTSVILLE  IRON  AND  STEEL  CO.;  READING  ROLLING 
MILL  CO.;  SHOENBERGER  STEEL  CO.;  SPANG  STEEL  AND  IRON  CO.;  WORTH  BROS. 

STRUCTURAL    STEEL. 

Process  of         1.  Steel   may   be  made  by  either  the  Open-hearth   or  Bessemer 
Manufacture,  process. 

Testing.  2.  All  tests  and  inspections  shall  be  made  at  place  of  manufacture 

prior  to  shipment. 

Test-pieces.  3.  The  tensile  strength,  limit  of  elasticity,  and  ductility  shall  be 
determined  from  a  standard  test-piece  cut  from  the  finished  material. 
The  standard  shape  of  the  test-piece  for  sheared  plates  shall  be  as 
shown  by  the  following  sketch: 


_Parallel  Section 
Not  less  than  9" 


Aboiit 

i. 


fr- About-iS: x 

Piece  to  be  of  same  thickness  as  the  plate. 

On  tests  cut  from  other  material  the  test-piece  may  be  either  the 
same  as  for  plates,  or  it  may  be  planed  or  turned  parallel  throughout 
its  entire  length.  The  elongation  shall  be  measured  on  an  original 
length  of  8  inches,  except  when  the  thickness  of  the  finished  material 
5/16  inch  or  less,  in 'which  case  the  elongation  shall  be  measured  in  a 
length  .equal  to  sixteen  times  the  thickness;  and  except  in  rounds  of  5/8 
inch  or  less  in  diameter,  in  which  case  the  elongation  shall  be  measured 
in  a  length  equal  to  eight  times  the  diameter  of  section  tested.  Two 
test-pieces  shall  be  taken  from  each  melt  or  blow  of  finished  material, 
one  for  tension  and  one  for  bending. 

Annealed          4.  Material  which  is  to  be  used  without  annealing  or  further  treat- 

Test-pieces.  ment  is  to  be  tested  in  the  condition  in  which  it  comes  from  the  rolls. 

When  material  is  to  be  annealed  or  otherwise  treated  before  use,  the 

specimen  representing  such  material  is  to  be  similarly  treated  before 

testing. 


*  These  specifications,  as  amended  from  year  to  year  by  the  manufacturers  themselves,  are  likely 
to  come  into  very  general  use,  since  any  deviation  from  them  will  involve  additional  expense.— J.  B.  J. 


768 


APPENDIX. 


Marking. 


Finish. 

Chemical 
Properties. 


5.  Every  finished  piece  of  steel  shall  be  stamped  with  the  blow  or 
melt  number,  and  steel  for  pins  shall  have  the  blow  or  melt  number 
stamped  on  the  ends.     Rivet  and  lacing  steel  and  small  pieces  for  pin- 
plates  and  stiffeners  may  be  shipped  in  bundles  securely  wired  together, 
with  the  blow  or  melt  number  on  a  metal  tag  attached. 

6.  Finished   bars   must   be  free   from   injurious   seams,   flaws,   or 
cracks,  and  have  a  workmanlike  finish. 

7.  Steel  for  /    ,r 

Maximum  Phosphorus  .08  per  cent. 


Railway  Bridges  : 
Steel  for  Buildings, 
Train  Sheds, 
Highway  Bridges, 
and  similar  structures: 


ir 

Maxinmm  Phosphorus  .10  per  cent. 


Properties 
Rivet  Steel. 


8-  Steel  sha11  be  of  three  Sradcs'  RlvET>  SOFT,  and  MEDIUM. 
9.  Ultimate  strength,  48,000  to  58,000  pounds  per  square  inch. 
Elastic  limit,  not  less  than  one  half  the  ultimate  strength. 
Elongation,  26  per  cent. 

Bending  test,  180  degrees  flat  on  itself,    without  fracture  on 
outside  of  bent  portion. 

Soft  Steef.       10.  Ultimate  strength,  52,000  to  62,000  pounds  per  square  inch. 
Elastic  limit,,  not  less  than  one  half  the  ultimate  strength. 
Elongation,  25  per  cent. 

Bending  test,   180  degrees  flat  on    itself,  without  fracture  on 
outside  of  bent  portion. 

Medium  Steef.      11.  Ultimate  strength,  60,000  to  70,000  pounds  per  square  inch. 
Elastic  limit,  not  less  than  one  half  the  ultimate  strength. 
Elongation,  22  per  cent. 

Bending  test,  180  degrees  to  a  diameter  equal  to  thickness  of 
piece  tested,  without  fracture  on  outside  of  bent  portion. 

Pin  Steef.  12.  Pins  made  from  either  of  the  above-mentioned  grades  of  steel 
shall,  on  specimen  test-pieces  cut  at  a  depth  of  one  inch  from  surface  of 
finished  material,  fill  the  physical  requirements  of  the  grade  of  steel 
from  which  they  are  rolled,  for  ultimate  strength,  elastic  limit,  and 
bending,  but  the  required  elongation  shall  be  decreased  5  per  cent, 
Eye-bar  Steel.  13.  Eye-bar  material,  1£  inches  and  less  in  thickness,  made  of  either 
of  the  above-mentioned  grades  of  steel,  shall,  on  test-pieces  cut  from 
finished  material,  fill  the  requirements  of  the  grade  of  steel  from  which 
it  is  rolled.  For  thicknesses  greater  than  1^  inches  there  will  be  allowed 
a  reduction  in  the  percentage  of  elongation  of  1  per  cent  for  each  1/8 
of  an  inch  increase  of  thickness,  to  a  minimum  of  20  per  cent  for 
medium  steel  and  22  per  cent  for  soft  steel. 

Full-size  Test    14.  Full-size  test  of  steel  eye-bars  shall  be  required  to  show  not  less 

of  Steel     than  10  per  cent  elongation  in  the  body  of  the  bar,  and  tensile  strength 

Eye-bars,     not  more  than  5000  pounds  .below  the  minimum  tensile  strength  re- 

quired in  specimen  tests  of  the  grade  of  steel  from  which  they  are 

rolled.     The  bars  will  be  required  to  break  in  the  body;  but  should  a  bar 

break  in  the  head,  but  develop  10  per  cent  elongation  and  the  ultimate 

strength  specified,  it  shall  not  be  cause  for  rejection,  provided  not  more 

than  one  third  of  the  total  number  of  bars  tested  break  in  the  head; 

otherwise  the  entire  lot  will  be  rejected. 

Variation  in       15.  The  variation  in  cross-section  or  weight  of  more  than  2-J  per  cent 
Weight.       from  that  specified  will  be  sufficient  cause  for  rejection  except  in  the 
case  of  sheared  plates,  which  will  be  covered  by  the  following  permissible 
variations  : 

a.  Plates  12^  Ibs.  or  heavier,  when  ordered    to  weight,   shall  not 
average  more  variation  than  2£  per  cent,  either  above  or  below  the 
theoretical  weight. 

b.  Plates  from  K)  to  12£  Ibs.,  when  ordered  to  weight,  shall  not 
average  a  greater  variation  than  the  following  : 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL. 


769 


Up  to  75  inches  wide,  2£  per  cent  either  above  or  below  the  theoretical 
weight. 

75  inches  and  over,  5  per  cent,  either  above  or  below  the  theoretical 
weight. 

c.  For  all  plates  ordered  to  gauge  there  will  be  permitted  an  average 
excess  of  weight  over  that  corresponding  to  the  dimensions  on  the  order 
equal  in  amount  to  that  specified  in  the  following  table : 

TABLE    OF   ALLOWANCES   FOR   OVERWEIGHT   FOR   RECTANGULAR 
PLATES    WHEN    ORDERED   TO    GAUGE. 

The  weight  of  1  cubic  inch  of  rolled  steel  is  assumed  to  be  .2833  pound. 


PLATES  1/4"  AND  OVER  IN  THICKNESS. 

PLATES  UNDER  1/4"  IN 
THICKNESS. 

Thicknes 
of  Plate 

1/4  i 
5/16 
3/8 
7/16 
1/2 
9/16 
5/8 
Over  5/8 

s 
:. 

Width  of  Plate. 

Thickness 
of  Plate. 

Width  of  Plate. 

Up  to  75  in. 

75  to  10 

14  perc 
12 
10 

8 

? 

5 

Oin. 
ent. 

Over  100  in. 

Up  to  50  in. 

50  in.  and 
above. 

10  perc 

8 

(5 
5 
4* 

3* 

ent. 

18  perc 
16 
13 
10 
9 

88» 

6* 

ent. 

1/8  up  to  5/32 
5/32      "    3/16 
3/16      "     1/4 

10  percent. 

S*            u 

15  percent. 

12*       " 
10 

STRUCTURAL  CAST   IRON. 

1.  Except  where  chilled  iron  is  specified,  all  castings  shall  be  tough 
gray  iron,  free  from  injurious  cold-shuts  or  blow-holes,  true  to  pattern, 
and  of  a  workmanlike  finish.  Sample  pieces,  one  inch  square,  cast 
from  the  same  heat  of  metal  in  sand-moulds,  shall  be  capable  of  sus- 
taining on  a  clear  span  of  4  feet  8  inches  a  central  load  of  500  pounds 
when  tested  in  the  rough  bar 

SPECIAL   OPEN-HEARTH   PLATE   AND   RIVET    STEEL. 

Testing  and        1.  All  tests  and  inspections  shall  be  made  at  place  of  manufacture 

Inspection,    prior  to  shipment. 

Test-pieces.        2.  The  tensile  strength,  limit  of  elasticity,  and  ductility  shall  be 

determined  from  a  standard  test-piece  cut  from  the  finished  material. 

The  standard  shape  of  the  test-piece  for  sheared  plates  shall  be  as 

shown  by  the  following  sketch: 


( 

Parallel  Section                ^ 

<-About-3->j       oj 

!    N 

Not  less  than  9* 

V 

About  2* 

K- 

^U-i-^-l^-Etc.— 
A-bout-i8—  • 

.-» 

Piece  to  be  of  same  thickness  as  the  plate. 


770 


APPENDIX. 


Annealed 
Test-pieces. 


Marking. 


Finish. 

Chemical 
Properties. 


On  tests  cut  from  other  material  the  test-piece  may  be  either  the 
same  as  for  plates,  or  it  may  be  planed  or  turned  parallel  throughout 
its  entire  length.  The  elongation  shall  be  measured  on  an  original 
length  of  8  inches,  except  when  the  thickness  of  the  finished  material 
is  5/16  inch  or  less,  in  which  case  the  elongation  shall  be  measured  in 
a  length  equal  to  sixteen  times  the  thickness;  and  except  in  rounds  of 
5/8  inch  or  less  in  diameter,  in  which  case  the  elongation  shall  be 
measured  in  a  length  equal  to  eight  times  the  diameter  of  section 
tested.  Four  test  pieces  shall  be  taken  from  each  melt  of  finished 
material;  two  for  tension  and  two  for  bending. 

3.  Material  which  is  to  be  used  without  annealing  or  further  treat- 
ment is  to  be  tested  in  the  condition  in  which  it  comes  from  the  rolls. 
When  material  is  to  be  annealed  or  otherwise  treated  before  use,  the 
specimen  representing  such  material  is  to  be  similarly  treated  before 
testing. 

4.  Every  finished  piece  of  steel  shall  be  stamped  with  the  melt 
number.     Rivet  steel  may  be  shipped  in  bundles  securely  wired  to- 
gether, with  the  melt  number  on  a  metal  tag  attached. 

5.  All  plates  shall  be  free  from  surface  defects  and  have  a  work- 
manlike finish. 

Maximum  Phosphorus  .04  per  cent. 
"          Sulphur 


6.  Extra  Soft  and 
Fire-box  Steel : 
Flange  or  Boil- 
er Steel  : 
Boiler  -  rivet 
Steel : 


.04 

Phosphorus  .06 
Sulphur         .04 


Physical 

Properties. 

Extra  Soft 

Steel. 


Phosphorus  .04    "       " 
"          Sulphur        .04   "       " 

7.  Steel  shall  be  of  four  grades— EXTRA  SOFT,  FIRE-BOX,  FLANGE  or 
BOILER,  and  BOILER-RIVET  STEEL. 

8.  Ultimate  strength,  45,000  to  55,000  pounds  per  square  inch. 

Elastic  limit,  not  less  than  one  half  the  ultimate  strength. 
Elongation,  28  per  cent. 

Cold  and  Quench  bends,  180  degrees  flat  on  itself;  without  frac- 
ture on  outside  of  bent  portion. 

Fire-box  Steel.       9.  Ultimate  strength,  52,000  to  62,000  pounds  per  square  inch. 
Elastic  limit,  not  less  than  one  half  the  ultimate  strength. 
Elongation,  26  per  cent. 

Cold  and  Quench  bends,  180  degrees  flat  on  itself,  without  frac- 
ture on  outside  of  bent  portion. 

Flange  or         10.  Ultimate  strength,  52,000  to  62,000  pounds  per  square  inch. 
Boiler-steel.  Elastic  limit,  not  less  than  one  half  the  ultimate  strength. 

Elongation,  25  per  cent. 

Cold  and  Quench  bends,  180  degrees  flat  on  itself,  without  frac- 
ture on  outside  of  bent  portion. 
Boiler-rivet       11.  Steel  for   boiler-rivets  shall  be  made  of  the  extra  soft  quality 

Steel.        specified  in  paragraph  No.  8. 

Variation         12.  For  all   plates   ordered  to  gauge   there  will  be   permitted  an 
when  ordered  average  excess  of  weight  over  that  corresponding  to  the  dimensions  on 
to  Gauge,     the  order  equal  in  amount  to  that  specified  in  the  following  table,  pro- 
vided no  plate  shall  be  rejected  for  light  gauge  measuring  .01"  or  less 
below  the  ordered  thickness  : 


SPECIFICATIONS  FOR  STRUCTURAL  STEEL. 


Ill 


TABLE   OF   ALLOWANCES   FOR   OVERWEIGHT    FOR    RECTANGULAR 

PLATES   WHEN    ORDERED   TO    GAUGE. 
The  weight  of  1  cubic  inch  of  rolled  steel  is  assumed  to  be  .2833  Ib. 

PLATES  i"  AND  OVER  IN  THICKNESS.    PLATES  UNDER  i"  IN  THICKNESS. 


Thickness  of 
Plate. 

Width  of  Plate. 

Thickness 
of  Plate. 

Width  of  Plate. 

Up  to 
75  in. 

75  in.  to 
100  in. 

Over 
100  in. 

Up  to 
50  in. 

5o  in.  and 
above. 

1/4  inch 

5/16    " 

3/8     " 
7/16    " 

10  per  cent 

8    "      " 

14  per  cent 

13    "      " 
10    "      " 

18  per  cent 
16    "      " 
13    "      " 

1/8  up  to  5/32 
5/32     "     3/16 
3/16     "       1/4 

10  per  cent 

8*  !',   !! 

15  per  cent 

12i  "      " 
10    "      " 

9/16    " 
5/8     » 
Over  5/8    " 

5    "      " 
4J  "      " 

6i  "      " 

9    "      " 

8*  "      " 

3J  "      " 

5    "      " 

6J  "      " 

Variation         13.  Plates  121  Ibs.  or  heavier,  when   ordered  to  weight,    shall  not 
when  ordered  average  more  variation  than  2%  per  cent,  either  above  or  below  the 
to  Weight,    theoretical  weight. 

Plates   from  10  to  12£  Ibs.,   when   ordered   to  weight,  shall  not 
average  a  greater  variation  than  the  following: 

Up  to  75  inches  wide,  24-  per  cent  either  above  or  below  the  theo- 
theoretical  weight. 

75  inches  and  over,   5  per  cent  either  above  or  below  the  theo- 
retical weight. 


INDEX 


A, 


.brasion  tests  of  stone,  results  of,  645 
Absorption  test  of  stone,  636 
Acid  and  basic  open-hearth  processes  com- 
pared, 142 
Added  material  on  one  side  of  member, 

effects  of,  36 
Adhesion  of  natural  to  Portland  cement, 

598 

Adhesion  tests  of  cement,  449 
Adhesive  force  of  nails  in  oak  wood,  689 
Adhesive  strength   of  cement-mortars  to 

various  substances,  597 
Age  (in  storage),  effect  of,  on  the  strength 

of  cement,  593 
Albert-Jay  of  wire  rope,  701 
Alloys,  the  manufacture  of  the  more  use- 
ful: 

nature  of  metallic  alloys,  173 
the  copper-zinc-tin  alloys,  174,  550,  552 
the  brasses — copper  and  zinc,  176,  550 
Delta-metal,  177,  56" 
Tobiu  bronze,  178,  554,  556 
the  bronzes— copper  and  tin,  178,  550, 

565 

phosphor  bronze,  178,  554,  556 
silicon  bronze,  179 
aluminum  bronze,  179,  555,  556 
hardened  aluminum,  180 
fusible  alloys,  180 
Aluminum : 

general  properties  of,  173 
how  hardened,  180 
in  steel,  180 
'Aluminum  bronze  : 
how  made,  179 
strength  of,  555t 
Angular  deformation  under  direct  stress, 


Annealing  copper  wire  and  plate,  550 
Annealing  steel,  146,  153,  168,  170,  731 

effect  of,  on  strength  qualities,  498,  501 
Annual  rings  in  wood,  207 
Apparent  elastic  limit,  12,  18,  309 
Areas  of  contact  between  car- wheels  and 

rails,  506 

Ash  (species  of)  in  the  U.  S.,  279 
Aspen  in  the  U.  S.,  281 
Autographic  stress-diagram  apparatus,  344 
Axles  : 

steel,  tested  by  cold  bending,  517 
wrought  iron  and  steel,   temperature 
tests  on,  563 

X)ach's  compressometer,  355 

Bach's  tests  on  concrete  columns  or 
prisms,  601 

Bacle"s  comparative  analysis  of  recommen- 
dations of  the  Conventions  and  of  the 
French  Commission,  737 

Basic  and  acid  open-hearth  processes  com- 
pared, 142  • 

Basswood  in  the  U.  S.,  281 

Bauschinger,  Prof.  Johann,  biographical 
sketch  of,  723 

Bauschinger's  mirror  extensometer,  342. 

Beams — see  Cross-bending  stress. 

Beams,  wooden  : 

tables  of  strength  of,  681,  682 
effect  of  size  on  strength  of,  672 

Bearing  resistance  of  iron  and  steel  plates, 
529 

Beech  in  the  U.  S. ,  282 

Bending,  cold — see  Cold  bending. 

Bessemer  and  open-hearth  steel  compared, 
142 

Bessemer  process  of  making  steel,  133 

773 


774 


INDEX. 


Billet  tests  of  steel,  valuable,  502 

Birch  in  the  U.  S.,  282 

Bleeding  Southern  piue,  effects  of,  672 

Boiling  test  of  cement,  417 

Brard's  process — see  Sulphate-of-soda  test. 

Brass,  strength  of,  550 

Brasses,  the  manufacture  of,  176 

Brick,  building  : 

strength  and  elastic  properties  of,  651, 
662 

strength  of  brick  piers,  with  stress-dia- 
grams, 651-659 
Brick,  "  vitrified,'1  (for  street-paving:) 

definition  of,  196 

clays  employed  in  manufacture  of,  197 

physical  properties  of  clays  for,  198 

preparation  of  the  clays,  200 

moulding  the  brick,  201 

drying  and  burning,  202 

annealing  after  burning,  203 

sorting  the  brick,  204 

kinds  of  tests  required,  456 
the  cross-breaking  test,  457 
the  crushing  test,  457 
the  rattler  test,  457,  460 
standard  tests  of  the  Nat'l  Brick 

Mfg.  Assoc.,  460 
results  of  tests,  660 
Brick  piers,  strength  of,  651-659 
Briquettes,  cement : 

forms  of,  432 

form  proposed  by  author,  434 

distribution  of  stress  in,  435* 
Brittle  and  plastic  materials,  24 
Brittle  materials  in  compression,  24 
Bronzes,  strength  of,  550-556 
Buckeye  (horse-chestnut)  in  the  U.  S.,  283 
Building-brick,  results  of  tests  of,  660,  662 
Burning  of  cements,  187,  194 

tests  for  thoroughness  of,  413 
Butternut-trees  in  the  U.  S.,  284 


c, 


Calcining  of  Portland  cement,  187,  194 
Callipers,  micrometer,  350 
Car-axles,  strength  of,  affected  by  temper- 
ature, 564 
Carbon  : 

in  cast  iron,  91 
in  iron  and  steel,  151 
change  in,  at  a  low  yellow  heat,  153 
effect  of,    on   the  tensile  strength  of 
steel,  156,  491-495 


Carbon,  effect  of,  on  ductility,  158,  491- 

495 

Carbonic-acid  gas,  effects  of,  on  the  hard- 
ening of  natural  and  slag  cements,  597 
Cast  iron  : 

historical  account  of,  87 
general  properties  of,  90 
carbon  in,  91 
silicon  in,  92 

influence  of,  on  mechanical  prop- 
erties, 94 

influence  of,  on  shrinkage,  95 
sulphur  in,  97 
phosphorus  in,  97 
manganese  in,  98 
pig-iron,  grading  of,  99 
foundry  practice,  100 
the  cupola,  100 
effect  of  remeltiug,  101 
the  moulds,  102 
moulding  sand,  104 
effect  of  size  and  shape,  105 
pipes  and  columns,  480 
shrinkage,  105 
shrinkage  stresses,  477 
the  mechanical  properties  of,  106 
hardness,  106 

hardness  and  strength,  107 
crushing  strength,  77,  473 
transverse  strength,  109,  475 
transverse  deflection,  372 
modulus  of  elasticity  of,  476 
tensile  strength,  110,  469 
Kirkakly's  results,  477 
strength  measured  by  shocks,  480 
malleable  cast  iron,  112 
defined,  112 

method  of  manufacture,  113 
mechanical  properties  of,  114 
magnetic  testing  of,  701 
Catalpa-trees  in  the  U.  S.,  284 
Cedars  of  the  U.  S.,  267 
Cellulose  from  wood,  249 
Cement,  natural  : 

manufacture  described,  182 
strength  of,  568 
mortar  of  : 

with     different     proportions     of 

sand,  579 

strength  of,  at  various  periods,  in 
terras  of  its  strength  at  28  days, 
573 


INDEX. 


775 


Cement,  natural : 
mortar  of  : 

hardening  in   air  and   in   water, 

576-7 
effect  of  regauging  after  set  begins, 

593 
effect  of  carbonic  acid  gas  on  the 

hardening  of,  597 
effect  of  freezing  on,  613 
effect  of  suit  on,  617-621 
adhesive  strength  of,  597 
effects    of    long    storage    on    the 

strength  of,  593 
Cement,  Portland  : 

historical  account  of,  183 
ingredients  of,  185 
clays  for,  185 

silica  and  its  compounds,  186 
alumina  for,  186 
sulphur  compounds  in,  187 
chemical  reactions  in  calcining,  187 
explanation  of  the  setting  and  harden- 
ing, 189 

sources  of  the  raw  materials  for,  191 
pulverizing  and  mixing  the  raw  ma- 
terials, 192 

processes  used  in  burning,  194 
grinding  the  clinker,  195 
strength  of,  572 
modulus  of  elasticity  of  mortars,  575, 

601 

hardening  in  air  and  in  water,  576-7 
mortar  of  : 

with  different  proportions  of  sand, 

579 
with  different  sizes  of  sand-grains, 

582 
economy  of  coarse  and  fine  sands, 

587 
relations    between    strength    and 

cost,  606 

porosity  of,  for  different  sands,  591 
strength  of,  at  various  periods,  in 
terms  of  its  strength  at  28  days, 
573 

compressive    strength    and    elas- 
ticity of,  603 
economy  of,  605 
effects  of  freezing  on,  612 
effects  of  salt  on,  617-621 
long  storage,  effect  of,  593 
regaugiug,  effect  of,  on  strength,  593 


Cement,  Portland  : 

adhesive  strength  of,  597 
concretes,  3 

strength  and  elasticity  of,  601 

economy  of,  605 

Wheeler's  tests  of  concrete  beams, 

608 

filtration  through,  612 
mixtures,  volumes  of,  608,  623 
in  sea-water,  623 
fire-resisting  properties  of  various  ' 

mixtures,  626 

cinder-concretes,  cost  and  proper- 
ties of,  627 

Cement,  slag — see  Slag-cement. 
Cement-testing  : 

standard  tests,  407 
fineness  of  grinding,  409 
thoroughness  of  burning,  413 
rate  of  setting,  415 
tests  for  soundness,  417 
the  boiling  test,  417 
tensile-strength  tests,  419 
fixed    relation    between     tensile    and 

compressive  strength,  419 
standard  consistency  of  briquettes,  420 
standard  sand  to  be  used,  424 
standard  consistency   of  cement-mor- 
tars, 429 

formation  of  the  briquettes,  430 
Bohme's  hammer,  432 
Tetmajer's  apparatus,  433 
form  of  the  briquette,  432 

standard   American  and    English 

form,  433 

standard  German  form,  434 
form  proposed  by  the  author,  434 
distribution  of  stress    over   mini- 
mum section,  435 
moulds  for  briquettes,  438 
clips,  their  bearings  and  mountings, 

438 

the  author's  design,  440 
tension-test  machines,  440 

standard  German  form,  441 
Fairbanks'  machine,  441 
Richie's  machine,  443 
Olsen's  machine,  444 
Porter's  machine,  445 
rate  of  applying  the  load,  effect  of, 

442 
eccentric  position  in  the  clips,  446 


776 


INDEX. 


Cement-testing  : 

compression  tests  of  cement,  446 

Swiss  machine  for  making,  448 
cross-bending  tests,  448 
adhesion  tests  of  cement,  449 
form  of  adhesion  briquette,  450 
variations  (normal)  of  volume  in  air 

and  in  water,  451 
French  Commission  recommenda- 
tion, 452 

permeability  test,  452 
decomposing  action  of  sea-water,  test 

for,  454 

Cement-testing  machines,  440 
Centre-punch,  double-pointed,  352 
Chains,  strength  of  wrought-iron,  489 
Changes  in  the  elastic  limits  by  stressing 

beyond  these  limits,  522 
Charcoal,  248 
Chemical  analysis  not  adequate  to  explain 

mechanical  qualities  of  steel,  150-154 
Chemical  composition  of  wood,  246 
Chemical  constituents,  limiting  values  al- 
lowable in  steel,  167 
Chemical  tests  of  stone,  635 
Cherry-trees  of  the  U.  S.,  285 
Chestnut-trees  of  the  U.  S.,  285 
Cinder-concrete    mixtures,    strength    and 

economy  of,  627 
Cinder-concrete  with  metal  base,  strength 

of,  629 
Clays  : 

for  Portland  cement,  185 
for  paving-brick,  197 
Cleavability  of  wood,  243 
Clinker-cement,  187,  195 
Clips  for  cement  briquettes,  438 

the  author's  design,  440 
Coarse  particles  in  cement  have  no  cement- 
ing quality,  409 
Coffee-trees  of  the  U.  S.,  286 
Cold-bending  tests  : 

character  and  significance  of,  394 
methods  of  making,  395 
preparation  of  the  specimen,  397 
comparison  of  results  from,  with  those 

from  tension  tests,  399 
combined    specified    requirements    in 

tension  and  cold  bending,  402 
comparison  of   results   from    tension, 
impact,     and     cold     bending, 
403 


Cold-bending  tests: 
of  steel  axles,  518 
of  steel  wire,  697 
Columns: 

cast-iron,  defects  in,  481 

effect  of  the  addition  of  material  to 

one  side  of,  36 
eccentric  loading  on,  36 
tests  of,  359 
strength  of,  360 

Consid6re's  results,  361 
Tetmnjer's  results,  364 
formulae  for,  366 
Columns,  wooden  : 
tests  of,  682-689 
formulae  for,  683-4 

Composite  (concrete  and  steel)  beams  com- 
puted, 72 

Compression-members — see  Columns. 
Compression  tests,  24 

two  classes  of  materials,  24 
on  plastic  materials,  24 
on  brittle  materials,  the  laws  of,  24 
angle  of  rupture  found,  25 
relation   of  crushing  strength   to 

shearing  strength,  28 
relation  of    strength    to   form    of 

specimen,  29 
relative  strength  of    prisms   and 

cubes,  31 
effect  of  loading  a  portion  of  the 

surface,  32 

test-specimens  for,  353 
bedding  of  specimens  in  the  test- 
ing-machine, 354 
eccentric  loading,  36 
effect  of  material  added  to  one  side  of 

column,  36 

compression  testing-machines,  355 

compressometers,  355 

Olsen's,  355 

Bach's,  355 

the  author's,  357 

Tetmajer's,  359 

tests  of  columns,  359 

compressive  strength  of  columns  the 

same     as     the     "apparent     elastic 

limit,"  360 

Considered  mounting  for  column  tests, 

361  ' 

Considered  results  of  column  tests,  362 
Tetmajer's      "       "        "         "  364-? 


INDEX. 


777 


Compression  tests  : 

ultimate  strength     formulae     for    col- 
umns, 366 

spring  testing-machines,  367 
compression  tests  of  cement,  446 

Swiss  machine  for  making,  448 
on  cast  iron,  77,  473 
on  steel,  502-509 
Compressive  strength  of  cement-mortar  as 

related  to  its  tensile  strength,  419 
Compressometers,  355 
Concrete  (see  also    Portland  cement  and 
Natural  cement) : 

compressive  strength  and  elasticity  of, 

603 

economy  of  various  mixtures,  605 

volumes    "         "  "         608 

Concrete  and  steel  in  combination,  strength 

computed,  72 
Concrete  beams,  mixtures  and  strength  of, 

608 

Concrete  mixture,  absolute  volumes  in,  623 
Concrete  structures  in  sea-water,  623 
Conductivity,  electrical,  table  of,  721 
Consistency  of  cement  mortars  in  test  bri- 
quettes, 420,  429 
Conventions,     comparative      analysis     of 

recommendations  of,  737 
Copper  : 

general  properties  of,  172 
strength  of,  548,  566 
annealing  of,  550 
Corrosion  of  iron  and  steel,  171 
Cotton  woods  of  the  U.  S.,  298 
Cross-bending    strength     of     timber    ex- 
plained, 236 
Cross-bending  stress : 

historical  sketch  of  theories,  42 
fundamental  equations  of  equilibrium, 

44 
relation  between  moment  of  resistance 

and  stress  on  extreme  fibre,  46 
homent  of  resistance  of  various  forms, 

48 

moment  of  resistance  beyond  the  elas- 
tic limit,  49 
distribution  of  stress  and  position  of 

neutral  axis  at  rupture,  50 
moduli  of  rupture  in   cross-breaking, 

51 

distribution  of    shearing  stress   in    a 
beam,  52 


Cross-bending  stress : 

beams     proportioned     for     shearing; 

stress,  56 

deflection   of  beams — general   formu- 
lae, 57 
beam  fixed  at  one  end  and  loaded  at 

the  other,  59 
beam  supported  at  the  ends  and  loaded 

at  the  centre,  60 

beam  supported  at  the  ends  and  uni- 
formly loaded,  61 

table  of  moments,  stresses,  and  deflec- 
tions, 61 

deflection  from  shearing  forces,  66 
determination  of  Young's  modulus  of 

elasticity,  67 
the    rational    designing     of    flitched 

beams,  68 

composite  concrete  and  steel  beam,  72 
flat  plates  uniformly  loaded,  73 
resilience  of  beams,  83 
Cross-bending  tests 
objects  of,  369 
essential  conditions  of,  369 
machines  for,  370 
deflection  essential  when  testing  cast 

iron,  372 
computed    strength    in     pounds     per 

square  inch,  373 

modulus  of  elasticity  (stiffness),  374 
of  cast  iron,  109,  475 
of  cement,  448 

Crucible  process  of  making  steel,  133 
Crushing— see  Compression. 
Crushing  strength  a  function  of  shearing 

strength,  28 
Crystalline  fractures  in  wrought  iron,  the 

causes  of,  120 

Cubes  and  prisms,  relative  strength  of,  31 
Cucumber-tree,  301 
Cutting  up  logs  in  the  U.  S.  timber  tests, 

464 
Cylinders  on  planes,  elastic-limit  loads  of, 

508 
Cypress  of  the  U.  S.,  269 


D, 


'ecay  of  wood  : 
produced  by  fungus-growth,  250 
prevention  of,  252 

Decomposing  action  of  sea- water  on  cement- 
mortar,  test  of,  454 
Defects,  microscopic,  in  steel,  537 


778 


INDEX. 


Deflection  of  beams,  57 

table  of,  61 

from  sheaving  forces,  66 
Deformation  : 

defined,  2 

various  kinds  of,  4 

longitudinal  and  lateral,  under  direct 
stress,  5 

of  volume,  5 

significant  limits  of,  806 
Deformation,  angular,  under  direct  stress,  6 
Delta-metal  : 

strength  of,  at  various  temperatures, 
566 

how  made,  177 

Distillation  products  of  wood,  248 
Distribution,  geographical,  of  the  Southern 

pines,  684 
Drifting  tests : 

their  character  aud  significance,  406 

specification  for,  406  , 
Drying  timber,  224,  676 
Durability  of   wood,  relative,  of  different 
species,  250,  253 

Jtljccentric  loading,  effects  of,  36 
Eccentric   position   of   briquette   in   clips, 

effects  of,  446 
Economy    of    cement-concrete    mixtures, 

605,  627 

Elastic  aud  plastic  bodies  defined,  1 
Elastic  field   destroyed   by  overstraining, 

522 
Elastic  limit  : 

defined,  18,  306 

absolute  limits  unsatisfactory,  308 

the  "apparent  elastic   limit,"  12,  18, 

309 

of  wrought  iron  in  tension,  486 
of  wrought  iron  after  stressing  beyond 

the  elastic  limit,  486-488 
of  steel  in  tension,  491-496 
of  steel  in  compression,  504 
of  steel  cylinders  on  planes,  508 
of  steel  as  affected  by  loading  beyond 

the  elastic  limits,  512,  522 
of  nickel-steel,  516 
of  timber,  670 
Elastic  limits  changed  by  overstraining, 

486,  522 

Electrical  conductivity  of  metals,  721 
Eluisof  theU.  S.,  286 


Elongation  : 

how  distributed   in  a  steel  test-speci- 
men, 502 
of  tension  test-specimens,  Tetmajer's 

analysis  of,  317 
percentage  of,  21 
Emery  testing-machines,  328 
Extensorneters,  340 


actors  of  safety  with  timber,  680 
Fatigue  of  metals : 

fatigue   defined,  a  new  definition  of- 
fered, 537 

micro-flaws  in  steel,  537 
Wohler's  tests  and  appliances,  539 
results  of  fatigue  tests,  541 
limits  of  max.  and  min.  stresses  for  an 
indefinite  number  of  repetitions,  541 
a  new  formula  for  dimensioning,  545 
Filtration  through  concrete,  612 
Fineness  of  grinding  of  cements,  signifi- 
cance and  tests,  409 
Fir  of  the  U.  S.,  269 
Fire-resisting  qualities  of  different  kinds  of 

concrete,  625 

Flat    plates    uniformly    loaded    approxi- 
mately computed,  73 
Flaws,  microscopic,  in  steel,  537 
Flexibility  of  wood,  244 
Flitched  beams,  the  design  of,  68 
Forging  under  a  light  hammer,  effects  of, 

517 
Form  of  specimen  a  function  of  crushing 

strength,  29 
Formulae  : 

for  the  ultimate  strength  of  columns, 

366,  683 
for  dimensioning  for  repeated  loads, 

545 

Foundry  practice — see  Cast  iron. 
Fractured  specimens  : 
of  timber,  241 
of  car  axles,  563 
of  wrought-iron  and  steel,  398 
Freezing,  effects  of,   on   cement-mortars, 

613 

Freezing  tests  of  stone,  633 
French  Commission,  report  of,  compared 
with  resolutions  of  the  Conventions,  737 
Frictional  resistance  : 
of  riveted  joints,  525 
per  square  inch  of  rivet  area,  527 


INDEX. 


779 


Fuel  value  of  wood,  247 
Fusible  alloys,  180 

augiug  implements,  352 
Geographical    distribution    of     Southern 

pines,  684 

Gneiss — see  Granite. 
Grains  of  wood,  215 
Granites  and  gneisses: 
structure  of,  630,  631 
strength  of,  640,  643.  645 
resistance  to  abrasion,  650 
Gray's  autographic  stress-diagram  appara- 
tus, 346 

Grinding  of  cement-clinker,  195 
Gripping  devices,  324 
Grooved  sections,  tensile  strength  of,  514, 

530 
Gum-trees  of  the  U.  S. ,  288 


H, 


.ackberry-trees  of  the  U.  S.,  289 
Hardening  of  cement-mortars  in  air  and  in 

water,  576-577 
Hardening,    tempering,  and  annealing  of 

steel,  168,  170,  731,  734 
Hardness  tests: 

hardness  defined,  381 
test  for  resistance  to  indentation,  381 
test  for  resistance  to  abrasion,  383 
Hardness  of  timber,  243 
Heart-wood,  207,  255 
Hemlock  of  the  U.  S.,  271 
Hickory-trees  of  the  U.  S.,  289 
Holly-trees  of  the  U.  S.,  291 
Hysteresis,  magnetic,  of   iron   and  steel, 
101 

JL  beams  and  plate  girders  tested  and  com- 
pared with  specimen  tests,  518 

Immersion,  long,  effects  of,  on  the  strength 
of  timber,  677 

Impact  stresses  for  given  deformations,  79 

Impact  tests: 

give  no  absolute  results,  80 

objects  of,  375 

essential  conditions  of,  376 

the  energy  of  the  blow,  376 

the  pendulum  test  standardized,  377 

impact  testing-machines,  379 

compared  with  cold-bending  tests,  403 

Impact  tests  on  car-axles,  564 

Impact  testing  machines,  379 


Iron    (see    also  Cast  iron,  Wrought  iron, 

and  Steel): 
historical  account  of  its  manufacture, 

87 

classification  of  iron  and  steel,  88 
magnetic  testing  of,  703 
micrographic  analysis  of,  725 
structural  constituents  of,  734 
Ironwood-trees  of  the  U.  8.,  283 


K, 


.eep's  testing-machine,  380 
Keep's  diagrams  of   the  strength  of  cast 

iron,  95,  96 

Kennedy's  shearing-test  apparatus,  386 
Key  to  wood  species  based  on  wood  struc- 
ture, 254,  258 


lampblack  from  wood,  249 

Larch  (tamarack)  of  the  U.  S.,  272 

Lauuhardt's  and  Weyrauch's  formulae  re- 
placed by  one  new  formula,  545 

Lateral  deformation  under  direct  stress,  •*> 

Length  of  reduced  section,  etfect  of,  514 

Lime,  hydraulic,  182 

Lime,  manufacture  of,  181 

Lime-mortar,  hardening  of,  181 

Limestone  and  marble: 
structure  of,  630,  631 
strength  of,  640,  643,  645 
resistance  to  abrasion,  650 

Limit  of  elasticity—*^  Elastic  limit. 

Limits  of  stress  for  indefinite  number  of 
repetitions,  541 

Loading,  effects  of  rate  of,  305 

Loads  suddenly  imposed,  81 

Locust-trees  of  the  U.  S.,,291 

Long  storage,  effect  of,  on  the  strength  of 
cement,  593 

Louisville  cement,  strength  of,  569,  570 

Low  red  heat,  effects  of  finishing  steel  at, 
499 


M, 


jjJ-achines,  testing,  general  requirements 

for,  304 

Magnetic  testing  of  iron  and  steel: 
magnetic  properties  defined,  703 
permeability,  703 
unit  of  manetizing  force,  703 
unit  of  magnetization,  703 
hysteresis,  703 

Steinmetz     law     ou     hysteresis, 
705 


780 


INDEX. 


Magnetic  testing  of  iron  and  steel: 
methods  of  testing,  705 

measurement  of  permeability,  705 
ring  method,  706 
divided-bar  method,  708 
double-bar  method,  709 
magnetic- bridge  method,  710 
voltmeter  method,  711 
permeameter  method,  712 
magnetic  balance,  712 
measurement  of  hysteresis,  713 
miscellaneous  methods,  718 
ring  method,  713 
E wing's  hysteresis-tester,  714 
results  of  tests,  716 

development  due  to  testing,  716 
conditions  affecting  magnetic  quality, 

718 

conductivity  data,  721 
importance  of  testing,  722 
Magnetization,  unit  of,  703 
Magnetizing  force,  unit  of,  703 
Magnolia-trees  of  the  U.  S.,  300 
Manganese: 

in  cast  iron,  98 
in  steel,  101,  162 
Manganese  bronze,  strength  of,  at  various 

temperatures,  566 
Malleable  iron — see  Cast  iron,  112 
Maple-trees  of  the  U.  S.,  291 
Marshall's  extensometer,  340 
Martel's  law  of  indentations,  382 
Mechanical    properties  of  timber,   133   to 

245 
Mechanical  tests  in  general,  302 

classification  of,  303 
Micro-flaws  in  steel,  537 
Micrographic  analysis  of  iron  and  steel,  725 
Micrometer-callipers,  350 
Microscopic  tests  of  stone,  635 
Milwaukee  cement,  strength  of,  569 
Modulus  of  elasticity  (Youjg's):   .* 
defined,  3 

of  volume  under  direct  stress,  6 
for  shearing  stress,  8 
determination  of,  fpom  beam  deflec- 
tions, 67,  374 
of  cast  iron,  476 
of  wrought  iron  (Fig.  392),  483 
of  steel,  509 

independent  of  other  qualities  in  steel, 
510 


Modulus  of  elasticity  (Young's) : 

of  cement-mortars  and  concretes,  575, 

601,  602,  603 
of  timber,  670 
Moisture  in  timber,  676 
distribution  of,  223 
test  for,  667 
reabsorbed,  668 

effects  of,  on  strength,  242,  667 
Molecular  structure  of  wrought  iron  and 

steel,  144 

Moments  of  inertia  of  various  forms,  48 
Moments  of  resistance  of  various  forms  of 

beams,  48 
Mortar,  cement : 

hardening  in  air  and  in  water,  576-7 
strength  of,  for  different  proportions  of 

sand,  579 

strength  of,  for  different  sizes  of  sand- 
grains,  582 

strength  of,  at  various  periods  as  com- 
pared with  the  strength  at  28  days, 
573 

economy  of  coarse  and  fine  sands,  587 
with  artificial  compositions  of   sand 

589 
porosity  of,  as  dependent  on  the  sand 

used,  591 

adhesive  strength  of,  597 
compressive  strength  and  elasticity  of, 

603 

economy  of,  605 
effects  of  freezing  on,  613 
anti-freezing  mixtures,  615 
rates  of  setting  at  different  tempera- 
tures, 616 

effects  of  salt  on,  617-621 
fire-resisting  properties  of  various  mix- 
tures, 626 
Mortar,  lime  : 

hardening  of,  181 
Moulds  for  cement  briquettes,  438 
Muck  bars,  122 
Mulberry-trees  of  the  U.  S.,  293 


N, 


ails,  holding-force  of,  in  oak  wood,  689 
Natural  cement— see  Cement,  natural. 
Nickel-steel,  515 

Oak-trees  of  the  U.  S.,  293 
Olsen's  testing-?ppliances : 
testing-machines,  320 


INDEX. 


781 


Olsen's  testing-appliances: 

stress- diagram  apparatus,  349 
compressometers,  355 

Opeii-hearUi     and    Bessemer    steel,    com- 
pared, 142 

Open -hearth  process  of  making  steel,  138 
O sage-orange  trees  of  the  U.  S.,  298 
Outerbridge's   experiments    on   increasing 

the  strength  of  cast  iron,  480 
Overstraining  destroys  the  elastic  field,  522 
Overstrained  metal  restored  by  annealing, 
513 

JL  aving-brick — see  Brick,  vitrified. 
Paving-brick  tests,  456 

cross-breaking,  457 

crushing,  457 

rattler  test,  457,  460 

general  table  of  results,  660 
Pendulum  impact  testing-machines,  377 
Permeability,  magnetic,  of  iron  and  steel, 

703 

Permeability  (to   water),  test    of    cement- 
mortars  for,  452 

Persimmon-trees  of  the  U.  S.,  298 
Phosphor-bronze  : 

how  made,  178 

strength  of,  554,  556 
Phosphorus: 

in  cast  iron,  97 

in  wrought  iron  and  steel,  165-7 

in  bronze,  178,  554,  556 
Photomicrographs  of  steel,  736 
Pig  iron,  grading  of,  99 
Pillars — see  Columns. 
Pines  of  the  United  States  : 

soft,  274 

hard,  275 
Pine,  short-leaf  and  long-leaf,  identified  by 

geographical  distribution,  684 
Pipes,  cast  iron,  with  uusymmetrical  thick- 
ness, 481 

Plastic  and  elastic  bodies  defined,  1 
Plastic  and  viscous  materials,  24 
Plastic  materials  in  compression,  24 
Plate  girders,  tests  on,  518 
Poissou's  ratio  defined  and  values  given,  5 
Poplar-trees  of  the  U.  S.  (see  also  Tulip), 

298. 
Porosity  of  mortars  as  dependent  on  the 

quality  of  the  sand  used,  591 
Portland  cement— see  Cement,  Portland. 


Posts — see  Columns. 

Prisms  and  cubes,  relative  crushing  strength 

of,  31 

Puddling  process,  117 
Punching  and   shearing,  injurious  effects 

of,  532 

Punching  tests  of  steel  not  valuable,  500 
Puzzolana  cement— see  Slag-cements. 

V^uenching  and  annealing,  effects  of,  on 
low-carbon  steel,  500 


R 


,ails,  car-wheels  on,  506 
Kate  of  applying  load  : 

effects  of,  in  general,  305 

effect  in  cement-testing,  442 
Rattler  test  of  paving  brick,  457,  460 
Reduction  in  the  rolls,  effect  of  : 

on  strength  of  wrought-iron,  131,  483 

on  strength  of  steel,  496-498 
Reduction  of  area  in  tensile  tests,  23 
Reduction  of  area  on  steel  test-specimens, 

502 
Regaugings  after  set  has  begun,  effect  of, 

on  strength,  593 
Resilience  : 

defined,  75 

stored  in  elastic  bodies,  76 

a  measure  of  the  body  to  resist  shock, 

r*f» 

Iv 

areas  of  stress-diagrams,  82 

of  bodies  under  direct  stress,  83 

in  cross-bending,  83,  3/2 

in  torsion  ,  85 

comparative,  for    different    kinds    of 
stress,  86 

of  cast  iron,  478 
Resin  from  wood,  249 
Resonance  of  wood,  218 
Richie's  testing-machines,  320,  327 
Rivet-steel,  stress-diagram  of,  496 
Rodman's  apparatus  for  testing  hardness 

standardized  ,  296 
Rope,  wire  —  see  Wire  rope. 
Rosen  dale  cement,  strength  of,  568 
Rusting  —  see  Corrosion, 


O 
lO 


lOalt,  effect  of,  on  cement-mortars,  617-621 

Sand  in  cement-mortars  : 

standard  to  be  used  in  cement  tests,  424 
effect  of  different  sands  on  the  strength 
of  cement-mortar,  424 


782 


INDEX. 


Sand  in  cement-mortars: 

effect  of  increasing  proportions,  579 
"      "  varying  sizes,  582 
"      "  composition,  587,  589 
Sand-cement,  strength  of  mortar  of,  576 
Sandstones  : 

structure  of,  631,  632 

strength  of,  639,  640,  643,  645 

resistance  to  abrasion,  650 
Sap-wood,  207,  255 
Sassafras-trees  of  the  U.  S.,  300 
Scarfed   joints,  how  to   avoid,  in   riveted 

work,  533 
Sea-water,  effect  of,  on  cement-concretes, 

623 
Setting  of  cement,  189 

rate  of,  415 

automatically  recorded,  415 

retardation  of,  at  low  temperatures,  616 
Shaft  16  in.  diarn.  forged  under  a  light 

hammer,  517 

Shafts,  steel,  drawn  through  dies,  518 
Shearing  modulus  of  elasticity,  8 
Shearing  and  direct  stresses,  7 
Shearing  and   punching,  injurious  effects 

of,  533 
Shearing  strength  : 

governs  crushing  strength,  28 

of  wrought  iron,  485 

of  steel,  525 

of  timber,  240 
Shearing  stresses  : 

cases  of,  38,  385 

in  beams,  52 
Shearing  tests . 

essential  conditions  of,  385 

appliances  for  making,  386 

of  wrought  iron,  485 

of  steel,  525 
Shock- resistance  measured   by  resilience, 

76 
Shrinkage  of  timber  • 

explained,  227 

effects  of,  229 

amount  of,  232 
Sifting  cement,  410 
Silicon  : 

in  cast  iron,  92 

influence  of,  on  mechanical  properties, 
74 

influence  of,  on  shrinkage,  95 

on  iron  and  steel,  160 


Silicon  bronze,  how  made,  179 

Size    of    wooden    beams — effects    of,    on 

strength,  672 
Slag-cements  : 
described,  190 

long  storage,  effect  of,  on  strength,  594 
effect  of  carbonic-acid  gas  on,  596 
Slipping  of- riveted  joints,  527 
Soundness  test  of  cements,  417 
Specifications  for  iron  and  steel : 

of  American   Society  of   Civil  Engi- 
neers, 756 

of  Mr.  H.  H.  Campbell,  756 
of  American  steel  manufacturers,  767 
Specific  gravity: 
of  cements,  413 
of  wood,  219 

of  different  species  of  timber,  222 
of  stone,  637 

Spring  and  summer  wood,  208 
Spring  testing  machines,  367 
Spruces  of  the  U.  S  ,  277 
Standard  tests  of  paving-brick,  460 
Steel-: 

methods  cf  manufacture,  133 
the  crucible  process,  133 
the  Bessemer  process,  133 
the  open-hearth  process,  138 
comparison  of  basic  and  acid  open- 
hearth  processes,  142 
comparison  of  Bessemer  and  open- 
hearth  steel,  142 
molecular  structure  of  wrought  iron 

and  steel,  144 

fracture  showing  structure,  145 
as  affected  by  heat  treatment,  146 
mechanical  qualities  of  steel  of  various 

grades,  147 

not  fully  explained  by  its  chemi- 
cal composition,  150 
Influence  of  carbon  on  iron,  151 

combination  of  carbon  with  iron, 

i51 

found  in  three  forms,  151 
change  in  the  carbon  at  a  low  yel- 
low heat,  153 

hardening  and  tempering  steel,  153 
chemical  analyses  cannot  explain 

mechanical  effects,  154 
the  hardening  of  steel,  155 
effect    on    the    tensile    strength'* 
156 


INDEX. 


783 


Steel  : 

influence  of  carbon  on  iron  : 

auxiliary   effects  of    phosphorus, 

sulphur,  and  manganese,  157 
effect  on  ductility,  158 
elongation  and  tensile  strength,  159 
modulus  of  elasticity,  160 
the  compress! ve  strength,  160 
hardness  and  fusibility,  160 
influence  of  silicon  on  iron  and  steel, 

160 

influence  of   manganese  on  iron  and 
steel,  161 

of  small  percentages,  162 
manganese  steel,  162 
influence  of  sulphur  on  iron  and  steel, 
163 

on  red  shortness,  163 
on  tensile  strength  and  ductility, 

164 

influence  of   phosphorus  on  iron  and 
steel,  165 
conditions  of  phosphorus  in  iron, 

165 

effect  on  ductility,  166 
effect  on  static  strength,  167 
limiting  value  of  chemical  constituents 

allowable,  167 

hardening,  tempering,  and  annealing, 
168 

heat- changes  in  carbon  steel,  168 
hardening,  169 
tempering,  169 

effects  of  hardening  and  temper- 
ing, 169 
annealing,  170 

corrosion  of  iron  and  steel,  171 
strength  of,  in  tension  and  compres- 
sion, 490 

as  influenced  by  carbon,  491-495 
of  rivet- steel,  496 
as  affected  by  thickness  of  plate, 

496-8 

as  affected  by  annealing,  498,  501 
as  affected  by  finishing  at  a  low  red 

heat,  499 
as  determined  by  punching  tests, 

500 
as  affected  by  quenching  and  an- 

nealing,  500 

as  determined  by  the  trial- billet 
test,  502 


Steel  : 

elongation,  how  distributed  in  the  ten- 
sion test,  502 

reduction  of  area  in  the  tension  test,  502 
compressive    strength   in   the    elastic 

limit,  502 

elastic  limit  in  compression,  504 
areas  of  contact  between  car-wheels 

and  rails,  506 
elastic-limit    loads    of    cylinders    on 

planes,  508 
moduli  of    elasticity  in    tension  and 

compression,  509 
moduli  of    elasticity  independent   of 

other  qualities,  510 
effect  of  stressing  beyond  the  elastic 

limit,  512,  522 

over- stressed  metal  restored  by  anneal- 
ing, 513 

effect  of  varying  the  length  of  speci- 
men, 514 
nickel-steel,  515 

effect  of  forging  and  rolling,  517 
steel  welded  tubes,  518 
I  beams  and  plate  girders,  518 
variation   of    moduli  with  size   of  I 

beam,  520 

shearing  strength,  525 
irictionalresistanceof  riveted  joiuts,525 
friction  per  sq.  in.  of  rivet  area,  527 
bearing  resistance  of  plates,  529 
injurious    effects    of    punching    and 

shearing,  532 

influence  of  form  of  thread  in  screw- 
bolts,  533 

fatigue  tests  on,  Wohler's,  539 
micro-flaws  in,  537 
magnetic  properties  of,  defined,  703 

methods  of  testing  for,  705 
micrographic  analysis  of: 
popular  account  of,  725 
technical  treatment  of,  728 

constituents  of  iron  and  car- 
bon steel,  728 

micrographs      of     steel     de- 
scribed, 730 
annealing,   general   influence 

of,  on  mild  steels,  731 
general  theory  of  the  structure 

of  steel,  734 

structure  of  hardened  steels. 
734 


784 


INDEX. 


Steel : 

photomicrographs  of  steel,  736 
specifications  for  : 

by  American  Society  of  Civil  En- 
gineers, 756 

by  Mr.  H.  H.  Campbell,  756 
by  American  steel  manufacturers, 

767 
Steel  and  concrete  in  combination,  strength 

computed,  72 
Steel  axles  drawn  through  dies  and  tested 

in  cold  bending,  518 

Steiumetz  law  on  magnetic  hysteresis,  705 
Stiffness  of  timber,  234 
Stone: 

crushing  test  of,  24,  29,  31,  355,  456 
crushing  strength  of,  637-645 
elastic  properties  of,  642 
structure  of  building,  630 
microscopic  views  of,  631 
"          study  of,  635 
weathering  of,  632 
freezing  tests  of,  633 
sulphate-of-soda  test,  634 
chemical  tests  of,  635 
absorption  test  of,  636 
specific-gravity  test,  637 
abrasion,  results  of  tests  of,  645 
Bauschinger's  abrasion  apparatus,  649 
Stone's  tests  of  wire  and  wire  rope,  698 
Storage,  long,  effect  of,  on  the  strength  of 

cement,  593 

Strain  defined  as  deformation,  2 
Strength  moduli  of  I  beams  and  plate  gir- 
ders, 520 

Strength  of  timber,  670-685 
Stress  and  deformation  defined,  2 

proportional  inside  elastic  limit,  2 
various  kinds  of,  4 
Stress-diagrams : 

indicate  resistance  to  shock,  81 
for  impact  and  for  static  loads  corn- 
pared,  79 

autographic  apparatus  for  taking,  344 
Stressing  steel  beyond  the  elastic  limit, 

effect  of,  512 
Stresses    from    impact    and    from    static 

loads  for  equal  deformations,  79 
Structure  of  steel,  150,  728 
Structureof  wood,  205, 209, 212, 214, 254, 255 
Structure  of  wrought  iron  and  steel  com- 
pared, 144,  728 


Sulphate-of-soda  test  of  stone,  634 
Sulphur  : 

in  cast  iron,  97 

in  wrought  iron  and  steel,  163-4 
Sycamore- trees  of  the  U.  S.,  300 

JL  amarack  (larch)  of  the  U.  S.,  272 
Tannin  from  wood,  249 
Temperature,  effect  of,  on  the  time  of  set- 
ting of  cements,  408 

Temperature  effects    on    the    mechanical 
properties  of  metals  : 
as  shown  by  stress-diagrams,  on  steel, 

557 

on  iron  and  steel,  557-565 
on  copper  and  bronze,  565 
on  delta-metal,  567 
Tensile     and     compressive     strength     of 

cement-mortars  compared,  419 
Tensile  tests  . 

general  phenomena  concerning,  10 
represented  by  stress- diagrams,  10 
significant  points  of  stress-diagrams,  n 
the  elastic  limit  in,  11,  18,  306 
the  apparent  elastic  limit,  12,  18,  309 
the  yield-point,  12,  18 
significant  results  of,  17,  312 
modulus  of  elasticity,  17 
elastic  limit,  18,  306 
"  apparent  elastic  limit,"  18,  309 
ultimate  strength,  21 
percentage  of  elongation,  21,  31" 
reduction  of  area  of  cross-section, 

23 

selection  of  the  test-specimen,  313 
preparation  of  the  test-specimen,  313 
standard  dimensions  of  test-specimens, 

315 

time-function  in,  320 
machines  for,  320 

Emery  machines,  328 
Olsen  machines,  320,  327 
Riehle  machines,  320,  327 
cement-testing  machines,  440 
gripping  devices,  324,  694 
extensometers,  340 
autographic  stress- diagram  apparatus, 

344 

micrometer  callipers,  350 
gauging  implements,  352 
compared  with  those  from  cold  bend- 
ing, 403 


INDEX. 


Tensile  tests 

of  cast  iron,  110,  469 
of  wrought  iron,  481 
of  steel,  490-502 
of  wire  and  wire  rope,  693 
Testing-machines,    general    requirements 

for,  304 
Tests  : 

mechanical,  in  general,  302 
classification  of,  303 
requirements  of  machines  for,  304 
effect  of  rate  of  loading,  305 
significant  limits  of  deformation, 

306 

limits  of  elasticity,  306 
all  absolute  elastic  limits  unsatis- 
factory, 308 

the  "apparent  elastic  limit,"  309 
tensile — see  Tensile  tests, 
compression— see  Compression  tests, 
cross  bending— see  Cross-bending  tests. 
impact — see  Impact  tests, 
hardness — see  Hardness  tests 
shearing — see  Shearing  tests, 
torsion — see  Torsion  tests, 
cold-bending—see  Cold-bending  tests. 
on  cement — see  Cement  tests, 
on  stone    and   brick — see    Stone  and 

brick  tests. 

on  timber — see  Timber  tests, 
on  cast  iron — see  Cast  iron, 
on  wrought  iron — see  Wrought  iron. 
on  steel— see  Steel, 
on  wire — see  Wire  and  wire  rope, 
magnetic— see    Magnetic     testing    of 

iron  and  steel. 
Test  specimens  : 

selection  and  preparation  of,  313 
standard  forms  of,  315 
Tetmajer's  compressometer.  359 
Thickness  of  rolled  forms,  influence  of,  on 

strength  qualities,  496-498 
Threads   on  screw-bolts,  influence  of  the 

lorin  of,  533 
Timber : 

structure  of  wood,  205,  209,  212,  214 

classification  of  timber-trees,  206 

sap  wood  and  heart  wood,  207 

annual  rings,  207 

spring  and  summer  wood,  208 

grains  of  wood,  215 

resonance,  218 


Timber . 

specific  gravity  or  weight,  219 
variation  of  weight  in  a  single  trunk, 

220 

weights  of  different  species,  222 
moisture  distribution,  223,  676 
drying  timber,  224 
dry  kiln  used,  226 
shrinkage  of  timber  explained,  227 
effects  of  shrinkage,  229 
amounts  of  shrinkage,  232 
mechanical  properties  of,  233 

stiffness,  or  modulus  of  elasticity, 

234 

cross-bending  strength,  236 
tension  and  compression,  238 
shearing,  240 

methods  of  failure  shown,  241 
influence  of  weight  and  moisture 

on  strength,  242,  667,  677 
hardness,  243 
cleavability,  243 
flexibility,  244 
toughness,  244 
practical  conclusions,  245 
chemical  composition  of  wood,  246 
wood  as  a  fuel,  247 
charcoal,  248 

products  of  wood  distillation,  248 
cellulose,  249 

resin,  turpentine,  and  lampblack.  249 
tannin,  249 

durability  and  decay  of  wood,  250 
all    decay  produced    by    fungus- 
growth,  250 

prevention  of  decay,  252 
relative     durabilky    of    different 

species,  253 
identification  of  different  species    of 

wood,  254,  684 

examination  of  the  structure  essen- 
tial, 254 

a  structural  key  to  species,  254 
characteristic  structural  features, 

255 

the  use  of  the  key,  257 
key  to  identification  of  species, 

258 

descriptive  list  of  the  more  important 
woods  of  the  U.  8.,  267 
coniferous  woods,  267 
cedar,  267,  670 


786 


INDEX. 


Timber 

descriptive  list  of  U.  S,  woods: 
coniferous  trees  : 

cypress,  269,  670 

fir,  269 

hemlock,  271 

larch  or  tamarack,  272 

pine,  273 

soft,  274,  670 
hard,  275,  670,  684 

redwood,  177 

spruce,  277 

bastard  spruce,  278 

yew,  279 
broad-leaved    woods  (deciduous): 

ash,  279,  670 

aspen  (see  also  Poplar),  281 

bass  wood,  281 

beech,  282 

birch,  282 

blue  beech,  283 

bais  d'arc— see  Osage  orange. 

buckeye,    or    horse-chestuut, 
283 

butternut,  284 

catalapa,  284 

cherry,  285 

chestnut,  285 

coffee-tree,  286 

cottonwood — see  Poplar. 

cucumber-tree — see  Tulip. 

elm,  286,  670 

gum,  288,  670 

hackberry,  289 

hickory,  289,  670 

holly,  291 

horse-chestnut — see  Buckeye. 

ironwood — see  Blue  beech. 

locust,  291 

magnolia— see  Tulip. 

maple,  291 

mulberry,  293 

oak,  293,  670 

osage  orange,  298 

persimmon,  298 

poplar  and  cottonwood    (see 
also  Tulip),  298 

sassafras,  300 

sycamore,  300 

tulip-wood,  300 

tupelo— see  Gum 

walnut,  301 


Timber : 

descriptive  list  of  U.  S.  woods  : 

broad-leaved  woods  (deciduous) : 
whitewood — see  Tulip, 
yellow  poplar — see  Tulip, 
tests  of  the  strength  of: 

the  U.   S.  timber  tests,  462,  664, 
666 

important  conclusions  drawn 

from,  462,  672,  677 
list  of  species  tested,  463,  665 
method  of  cutting  up  logs,  464 
cross-bending  test,  465 
crushing  endwise  test,  467 
crushing  across  the  grain,  468 
shearing  test,  468 
tension  test,  468 
moisture  test,  667,  676 
strength  of — results  of  tests,  664 
as  affected  by  moisture,  667 
tables  of  strength  moduli,  670-675 
effect  of  bleeding  (for  turpentine), 

672 
effect  of  size,  672 

"     "  reabsorbed  moisture,  676 
"     "  hot-air  drying,  676 
effect  of  very  high  temperatures 

and  pressures,  677 
effect  of  long  immersion,  677 
effect  of  varying  specific  gravity, 

or  weight,  677 
factors  of  safety,  680 
tables  of  safe  loads  for  wooden 

beams,  681,  682 
strength  of  wooden  columns,  682- 

689 

identification  of  short-leaf  and    long- 
leaf  pine,  684 
holding-force  of  nails  in  oak  wood, 

689 

Timber-trees  of  the  U.  S.,  list  and  descrip- 
tion of  the  most  important,  267 
Time-function  in  tension  tests,  320 
Tin,  general  properties  of,  173 
Tobin  bronze  : 

how  made,  177 
strength  of,  554,  556 
Torsion  : 

deformation  from,  40 
moment  of,  39 
resilience  of,  85  ' 
tests  by,  387 


INDEX. 


787 


Torsion  tests  : 

contrasted  with  shearing  tests,  387 

machines  for  making,  387 
Toughness  of  wood,  244 
Tubes,  welded  steel,  518 
Tulip- wood  trees  of  the  U.  S.,  300 
Turner's  diagrams    of    the    properties    of 

cast  iron,  94 

Turner's  apparatus  for  testing  hardness,  384 
Turpentine  from  wood,  249 

LJ  Itimate  strength  in  tension,  21 
Use  of  cement-mortars  after  set  has  begun, 

593 
U.  S.  timber  tests  : 

described,  462,  664 
species  tested,  463,  665 
conclusions  from,  462,  670-680 
mechanical  tests,  465,  664 
Utica  cement,  strength  of,  569 

V  icat's  needle  for  testing  the  rate  of  set- 
ting of  cements,  416 
Vitrified  brick — see  Brick,  vitrified. 
Volumetric  deformation,  5 
Volumetric  modulus  of  elasticity,  6 
Volume  variation  in  cement-mortars,  451 
Vulcanizing  process  of  treating  timber,  ef- 
fects of,  on  strength,  677 


W, 


alnut-trees  of  the  U.  S.,  301 
Water,  effect  of  varying  quantities  of,  on 

the  strength  of  cement,  420 
Weathering  of  building-stones,  633 
Weight,  specific,  of  timber,  219,  222 

effect  of,  on  strength,  242,  677 
Welded  steel  tubes,  518 
Welding  of  wrought  iron,  128 
Weyrauch's  and  Launhardt's  formulae  re- 
placed by  a  new  one,  545 
Wheels  (car)  on  rails,  areas  of  contact  of, 

506 

Whitewood— see  Tulip-tree. 
Wire  : 

tests  of,  697 

machines  for  testing,    328,   392,   697, 

698,  699 
strength  of,  309,  691,  693,  695 


Wire: 

Stone's  tests  of,  698 
Wire  rope  : 

tests  of,  693 
strength  of,  695,  700 
methods  of  laying  wire  in,  701 
Wohler's  'tests  and  appliances  on  fatigue 

of  metals,  539 
Wood— see  Timber. 
Wooden  beams — see  Beams,  wooden. 
Woods  of  the  U.  S.,  list  and  description 

of  most  important,  267 
Wrought  iron  : 
defined, 117 

methods  of  manufacture,  117 
the  puddling  process,  117 
oxidation  in  puddling,  119 
details  of  the   puddling  process, 

120 

production  of  muck-bars,  122 
piling  and  reheating,  123 
the  rolls,  123 
effect  of    numerous   pilings  and 

rollings,  123 
finished  sections,  124 
imperfections  in  finished  iron,  125 
mechanical  properties  of,  125 

crystalline  fractures,  the  causes  of, 

125 

welding  of,  128 
effect  of  reduction  in  the  rolls  on 

the  strength,  131 
tensile  strength,  481 

across  the  grain,  481 

as  affected  by  pulling  speed, 

484 

compressive  strength,  484 
shearing  strength,  485 
effect  of  stressing  beyond  the  elas- 
tic limit,  486 
chains,  strength  of,  489 
magnetic  testing  of,  703 

J_  ellow  poplar  trees  of  the  U.  S.,  300 

Yew  of  the  U.  S.,  279 


Z 


Ljinc,  general  properties  of,  172 


'' 


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SEP  26  1939A 


MAY 


OCT2     19766.01 


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J6  0  1 199] 


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LD  21-95«i-7,'3' 


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